[Federal Register Volume 77, Number 84 (Tuesday, May 1, 2012)]
[Proposed Rules]
[Pages 25792-25828]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2012-10016]
[[Page 25791]]
Vol. 77
Tuesday,
No. 84
May 1, 2012
Part II
Department of the Interior
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Fish and Wildlife Service
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50 CFR Part 17
Endangered and Threatened Wildlife and Plants; 12-Month Finding on a
Petition To List the Sonoran Desert Area Bald Eagle as Threatened or
Endangered; Proposed Rule
Federal Register / Vol. 77 , No. 84 / Tuesday, May 1, 2012 / Proposed
Rules
[[Page 25792]]
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DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
50 CFR Part 17
[Docket No. FWS-R2-ES-2008-0059; 4500030113]
Endangered and Threatened Wildlife and Plants; 12-Month Finding
on a Petition To List the Sonoran Desert Area Bald Eagle as Threatened
or Endangered
AGENCY: Fish and Wildlife Service, Interior.
ACTION: Notice of 12-month petition finding.
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SUMMARY: We, the U.S. Fish and Wildlife Service (Service), announce a
12-month finding on a petition to list the Sonoran Desert Area
population of bald eagle (Haliaeetus leucocephalus) as threatened or
endangered under the Endangered Species Act of 1973, as amended (Act).
After review of the best available scientific and commercial
information, we find that listing the Sonoran Desert Area population of
bald eagle does not qualify as a distinct population segment (DPS) and
listing the Sonoran Desert Area population of bald eagle is not
warranted at this time.
DATES: The finding announced in this document was made on May 1, 2012.
ADDRESSES: This finding is available on the Internet at http://www.regulations.gov at Docket Number FWS-R2-ES-2008-0059. Supporting
documentation we used in preparing this finding is available for public
inspection, by appointment, during normal business hours at the U.S.
Fish and Wildlife Service, Southwest Regional Office, 500 Gold Ave.
SW., Room 6034, Albuquerque, NM 87102. Please submit any new
information, materials, comments, or questions concerning this finding
to the above address.
FOR FURTHER INFORMATION CONTACT: Michelle Shaughnessy, Assistant
Regional Director, Southwest Regional Office (see ADDRESSES); by
telephone at 505-248-6920; or by facsimile at 505-248-6788. If you use
a telecommunications device for the deaf (TDD), please call the Federal
Information Relay Service (FIRS) at 800-877-8339.
SUPPLEMENTARY INFORMATION:
Background
Section 4(b)(3)(B) of the Act (16 U.S.C. 1531 et seq.) requires
that, for any petition to revise the Federal Lists of Endangered and
Threatened Wildlife and Plants that contains substantial scientific or
commercial information indicating that listing may be warranted, we
make a finding within 12 months of the date of our receipt of the
petition. In this finding we will determine that the petitioned action
is: (1) Not warranted, (2) warranted, or (3) warranted, but the
immediate proposal of a regulation is precluded by other pending
proposals to determine whether species are threatened or endangered
(warranted but precluded). Section 4(b)(3)(C) of the Act requires that
we treat a petition for which the requested action is found to be
warranted but precluded as though resubmitted on the date of such
finding, that is, requiring that we make a subsequent finding within 12
months. Such 12-month findings must be published in the Federal
Register.
This document constitutes our revised 12-month finding on a
petition to list the Sonoran Desert Area bald eagle. In this document,
the Sonoran Desert Area population is the name given to the entity
under evaluation for designation as a distinct population segment
(DPS). For the purposes of this assessment, the Sonoran Desert Area
population includes all bald eagle territories within Arizona, the
Copper Basin breeding area in California near the Colorado River, and
the territories of interior Sonora, Mexico, that occur within the
Sonoran Desert and adjacent transitional communities. For more detail
on the boundary of the DPS, see the discussion below under
Determination of the Area for Analysis.
Previous Federal Action
Bald eagles (Haliaeetus leucocephalus) gained protection under the
Bald Eagle Protection Act (16 U.S.C. 668-668d) in 1940 and the
Migratory Bird Treaty Act (MBTA) (16 U.S.C. 703-712) in 1972. A 1962
amendment to the Bald Eagle Protection Act added protection for the
golden eagle (Aquila chrysaetos), and the amended statute became known
as the Bald and Golden Eagle Protection Act (BGEPA). On February 14,
1978, the Service listed the bald eagle as an endangered species under
the Endangered Species Act of 1973, as amended (Act) (16 U.S.C. 1531 et
seq.) in 43 of the contiguous States, and as a threatened species in
the States of Michigan, Minnesota, Wisconsin, Oregon, and Washington
(43 FR 6230). On July 12, 1995, we published a final rule to reclassify
the bald eagle from endangered to threatened in the 43 States where it
had been listed as endangered and retain the threatened status for the
other 5 States (60 FR 36000).
On July 6, 1999, we published a proposed rule to delist the bald
eagle throughout the lower 48 States due to recovery (64 FR 36454). On
February 16, 2006, we reopened the public comment period to consider
new information received on our July 6, 1999 (71 FR 8238), proposed
rule to delist the bald eagle in the lower 48 States. On October 6,
2004, we received a petition from the Center for Biological Diversity
(CBD), the Maricopa Audubon Society, and the Arizona Audubon Council
requesting that the ``Southwestern desert nesting bald eagle
population'' be classified as a distinct population segment (DPS) under
the Act, that this DPS be reclassified from a threatened species to an
endangered species, and that we concurrently designate critical habitat
for the DPS under the Act. We announced in our 90-day finding on August
30, 2006 (71 FR 51549), that the petition did not present substantial
scientific or commercial information indicating that the petitioned
action may be warranted.
On January 5, 2007, the CBD and the Maricopa Audubon Society
(Plaintiffs) filed a lawsuit in the U.S. District Court for the
District of Arizona challenging the Service's 90-day finding that the
bald eagles nesting in the Sonoran Desert area of central Arizona did
not qualify as a DPS, and further challenging the Service's 90-day
finding that the population should not be uplisted to endangered
status.
On July 9, 2007 (72 FR 37346), we published the final delisting
rule for bald eagles in the lower 48 States due to recovery. This final
delisting rule also included the bald eagles located in the Sonoran
Desert. On August 17, 2007, the CBD and the Maricopa Audubon Society
filed a Motion for Summary Judgment in their January 5, 2007, lawsuit.
In early 2008, several Native American Tribes submitted amicus curiae
(``friend of the court'') briefs in support of the August 17, 2007,
Motion for Summary Judgment. The San Carlos Apache Tribe, Yavapai-
Apache Nation, and Tonto Apache Tribe submitted amicus curiae briefs to
the court on January 29, 2008; the Salt River Pima-Maricopa Indian
Community submitted an amicus curiae brief to the court on February 4,
2008; and the Fort McDowell Yavapai Nation submitted an amicus curiae
brief to the court on February 7, 2008.
On March 5, 2008, the court made a final decision in the challenge
to the Service's 2006 90-day finding, ruling in favor of the CBD and
the Maricopa Audubon Society. The court order (Center for Biological
Diversity v. Kempthorne, CV 07-0038-PHX-MHM (D. Ariz)), dated March 6,
2008, required
[[Page 25793]]
the Service to conduct a status review of the Desert bald eagle
population pursuant to the Act to determine whether that population may
qualify as a DPS, and if so, whether listing that DPS as threatened or
endangered pursuant to the Act is warranted. The court enjoined the
Service's application of the July 9, 2007 (72 FR 37346), final
delisting rule with respect to the bald eagles nesting in the Sonoran
Desert area of central Arizona pending that status review and 12-month
finding on the Plaintiffs' petition.
On May 1, 2008, to conform with the court's March 6, 2008, order,
we published a final rule listing the potential Sonoran Desert bald
eagle DPS as threatened under the Act (73 FR 23966). On May 20, 2008,
we published a Federal Register notice (73 FR 29096) initiating a
status review for the bald eagles nesting in the Sonoran Desert area of
central Arizona.
On February 25, 2010, the Service published its 12-month finding on
the October 6, 2004, petition, as required by the March 5, 2008, court
order (75 FR 8601). The Service found that the bald eagles nesting in
the Sonoran Desert area did not qualify as a DPS and, therefore, were
not a listable entity under the Act. Concurrent with publication of our
12-month finding, the Service filed a motion for dissolution of the
court's injunction. Plaintiffs asked the Court for leave to file a
supplemental complaint challenging the merits of the new 12-month
finding. By order dated September 30, 2010, the court denied the
Plaintiffs' request to file a supplemental complaint, and dissolved the
injunction. This had the effect of reinstating the provisions of the
delisting rule for the bald eagles nesting in the Sonoran Desert area
of central Arizona, thereby removing the bald eagles nesting in the
Sonoran Desert area of central Arizona from the List of Endangered and
Threatened Wildlife. (Center for Biological Diversity, et al. v.
Salazar, et al., 07-cv-00038-PHX- MHM, 2010 U.S. Dist. LEXIS 72664 (D.
Ariz. Sept. 30, 2010). On September 2, 2011, the Service published a
final rule to comply with the court's September 30, 2010, order.
On October 5, 2010, CBD and the Maricopa Audubon Society
(Plaintiffs) filed a new lawsuit in the U.S. District Court for the
District of Arizona, challenging the Service's February 25, 2010, 12-
month finding that the bald eagles nesting in the Sonoran Desert area
did not qualify as a DPS. On January 5, 2011, the court granted the San
Carlos Apache Tribe of Arizona's November 24, 2010, motion to intervene
as Intervenor-Plaintiff. On March 1, 2011, the court granted the Salt
River Pima-Maricopa Indian Community's January 12, 2011, motion to
intervene as Intervenor-Plaintiff.
On November 30, 2011, the court granted Plaintiffs' motions for
summary judgment to the extent they asserted the Service's 12-month
finding was procedurally flawed. The court order (Center for Biological
Diversity v. Kempthorne, CV 10-2130-PHX-DGC (D. Ariz)) required the
Service to produce a new 12-month finding by April 20, 2012, based on
information gathered in the status review already conducted. The court
order also directed the Service to address issues identified in the
order in the new 12-month finding, specifically whether the Service has
adopted a new interpretation of the DPS policy and provide a reasoned
explanation for why loss of the desert eagle would not result in a
significant gap in the range (assuming the Service reached this
conclusion in its new 12-month finding).
Public Information
As noted above, on May 20, 2008, the Service published a notice to
initiate a 12-month status review for the Sonoran Desert population of
bald eagle in central Arizona and northwestern Mexico, and a
solicitation for new information (73 FR 29096). To allow adequate time
to consider the information, we requested that information be submitted
on or before July 7, 2008. On January 15, 2009, a second Federal
Register notice (74 FR 2465) was published announcing the continuation
of information collection for the 12-month status review. In order to
allow us adequate time to consider and incorporate submitted
information, we requested that we receive information on or before July
10, 2009. Between May 2008 and February 2010, we received 31 responses
via http://www.regulations.gov, and 5 letters by U.S. mail.
Tribal Information
In accordance with Secretarial Order 3206, the Service acknowledges
our responsibility to consult with federally recognized Tribes on a
government-to-government basis. Over the course of the previous bald
eagle status review, we corresponded and met with various Tribes in
Arizona, all of whom support protection of the bald eagle under the
Act. On July 2, 2008, the Service and Tribal representatives from four
Western Apache Tribes and one Nation (White Mountain Apache, San Carlos
Apache, Tonto Apache Tribes, and Yavapai-Apache Nation) met to hear
testimony from cultural authorities on a variety of subjects, including
the history of the eagle in Arizona and the importance of the eagle to
the Apache people. At the request of Tribal representatives, this
meeting was recorded and incorporated into the administrative record
for the 12-month finding. On July 3, 2008, the Service met with members
of the Salt River Pima-Maricopa Indian Community, Gila River Indian
Community, Tohono O'Odham Nation, Ak-Chin Indian Community, Tonto
Apache Tribe, Fort McDowell Yavapai Nation, the Hopi Tribe, Pascua
Yaqui Tribe, Zuni Tribe, and the InterTribal Council of Arizona. This
meeting was held in Phoenix, Arizona, and a court reporter recorded the
meeting minutes. Members of the Tribes and nations present, however,
did not consider this meeting to constitute government-to-government
consultation pursuant to Secretarial Order 3206. On July 20, 2009, an
official consultation meeting between the Service and Salt River Pima-
Maricopa Indian Community occurred. Written comments were provided by
the Western Apache Tribes and Nation and the Salt River Pima-Maricopa
Indian Community on July 10, 2009.
Although comments from the Native American communities were
provided in writing, much of the knowledge about the bald eagle was
offered during the above-referenced face-to-face meetings. Native
American knowledge about the eagle is passed down orally from one
generation to the next, which is often referred to in the literature as
traditional ecological knowledge. Traditional ecological knowledge
refers to the knowledge base acquired by indigenous and local peoples
over many hundreds of years through direct contact with the
environment. Traditional knowledge is based in the ways of life, belief
systems, perceptions, cognitive processes, and other means of
organizing and transmitting information in a particular culture.
Traditional ecological knowledge includes an intimate and detailed
knowledge of plants, animals, and natural phenomena; the development
and use of appropriate technologies for hunting, fishing, trapping,
agriculture, and forestry; and a holistic knowledge, or ``world view,''
which parallels the scientific discipline of ecology (Inglis 1993, p.
vi).
Testimony by the Western Apache Tribes and Nation and Salt River
Pima-Maricopa Indian Community clearly demonstrates the importance of
the bald eagle to their culture, its relevance to their well-being, and
their respect for its power. Their testimony also
[[Page 25794]]
demonstrates the Western Apache and Salt-River Pima Maricopa knowledge
base of the bald eagle and its habitat. The Native American
relationship with the bald eagle in the Sonoran Desert Area predates
modern Western scientific knowledge of the bald eagle by thousands of
years (Lupe et al. pers. comm. 2008, p. 1). Given the expertise and
traditional ecological knowledge about the bald eagle in the Southwest
demonstrated by the Western Apache Tribes and Nation and Salt-River
Pima Maricopa Indian Community, we have incorporated this information
into our status review and 12-month finding.
Species Information
The bald eagle (Haliaeetus leucocephalus) is the only species of
sea eagle regularly occurring in North America (60 FR 35999; July 12,
1995). Literally translated, H. leucocephalus means white-headed sea
eagle. Bald eagles are birds of prey of the Order Falconiformes and
Family Accipitridae. They vary in length from 28 to 38 inches (in) (71
to 96 centimeters (cm)), weigh between 6.6 and 13.9 pounds (lbs) (3.0
and 6.3 kilograms (kg)), and have a 66- to 96-in (168- to 244-cm)
wingspan. Distinguishing features of adult bald eagles include a white
head, tail, and upper- and lowertail-coverts; a dark-brown body and
wings; and yellow irises, beak, legs, and feet. Immature bald eagles
are mostly dark brown and lack a white head and tail until they reach
approximately 5 years of age (Buehler 2000, p. 2).
Biology and Distribution
In many Western Apache groups, the bald eagle is called
Ist[lstrok]g[aacute][iacute], which translates to ``the white eagle''
and is distinguished from the golden eagle, which is called Itsa Cho or
``the big eagle.'' The bald eagle was first described in Western
culture in 1766 as Falco leucocephalus by Linnaeus. This South Carolina
specimen was later renamed as the southern bald eagle, subspecies
Haliaeetus leucocephalus leucocephalus (Linnaeus) when Townsend
identified the northern bald eagle as Haliaeetus leucocephalus
alascanus in 1897 (Buehler 2000, p. 4). By the time the bald eagle was
listed throughout the lower 48 States under the Act in 1978,
ornithologists no longer recognized the subspecies (American
Ornithologists Union 1983, p. 106).
The bald eagle ranges throughout much of North America, nesting on
both coasts from Florida to Baja California, Mexico, in the south, and
from Labrador to the western Aleutian Islands, Alaska, in the north.
Fossil records indicate that bald eagles inhabited North America
approximately 1 million years ago, but they may have been present
before that (Stalmaster 1987, p. 5). An estimated quarter to a half
million bald eagles lived on the North American continent before the
first Europeans arrived.
Though once considered endangered, the bald eagle population in the
lower 48 States has increased considerably in the last thirty years.
Regional bald eagle populations in the Northwest, Great Lakes,
Chesapeake Bay, and Florida have increased five-fold in the past 20
years. Bald eagles are now repopulating areas throughout much of the
species' historical range that were unoccupied only a few years ago.
The bald eagle is a bird of aquatic ecosystems. It frequents
estuaries, large lakes, reservoirs, major rivers, and some seacoast
habitats. Fish is the major component of its diet, but waterfowl,
gulls, and carrion are also eaten. The species may also use prairies if
adequate food is available. Bald eagles typically nest in trees, but
have also been documented nesting on cliffs, on the ground, in
mangroves, in caves, and in manmade structures (e.g., cell phone
towers). Trees must be sturdy and open to support a nest that is often
5 feet (ft) (1.52 meters (m)) wide and 3 ft (0.91 m) deep. Adults tend
to use the same breeding areas year after year, and often the same
nest, though a breeding area may include one or more alternate nests.
Nest shape and size vary, but typical nests are approximately 4.9 to
5.9 ft (1.5 to 1.8 m) in diameter and 2.3 to 4.3 ft (0.7 to 1.2 m) tall
(Stalmaster 1987, p. 53). In winter, bald eagles often congregate at
specific wintering sites that are generally close to open water and
offer good perch trees and night roosts.
Bald eagles are long-lived. One of the longest-living bald eagles
known in the wild was reported near Haines, Alaska, as 28 years old
(Schempf 1997, p. 150). In 2009, a female eagle nesting at Alamo Lake
in Arizona turned 30 years old (J. Driscoll, Arizona Game and Fish
Department (AGFD), pers. comm. 2009). In captivity, bald eagles may
live 40 or more years. It is presumed that once they mate, the bond is
long-term. Variations in pair bonding are known to occur. If one mate
dies or disappears, the other will accept a new partner.
Bald eagle pairs begin courtship about a month before egg-laying.
In the southern portion of its range, courtship occurs as early as
September, and in the northern portion of its range, as late as May.
The nesting season lasts about 6 months. Incubation lasts approximately
35 days, and fledging takes place at 11 to 12 weeks of age. Parental
care may extend 4 to 11 weeks after fledging (Hunt et al. 1992, p. C9;
Wood et al. 1998, pp. 336-338). The fledgling bald eagle is generally
dark brown except the underwing linings, which are primarily white.
Between fledging and adulthood, the bald eagle's appearance changes
with feather replacement each summer. Young, dark bald eagles may be
confused with the golden eagle, Aquila chrysaetos. The bald eagle's
distinctive white head and tail are not apparent until the bird fully
matures, usually at 4 to 5 years of age.
The migration strategies for breeding, nonbreeding, and juvenile or
subadult age classes of bald eagles will vary depending on geographic
location. Young eagles may wander widely for years before returning to
nest in natal areas. Northern latitude bald eagles winter in areas such
as the Upper Mississippi River, Great Lakes shorelines, and river
mouths in the Great Lakes area. For midcontinent bald eagles, wintering
grounds may be the southern States, and for southern latitude bald
eagles, whose nesting may begin in the winter months, the nonbreeding
season foraging areas may be the Chesapeake Bay or Yellowstone National
Park during the summer. Eagles seek wintering (nonnesting) areas
offering an abundant and readily available food supply with suitable
night roosts. Night roosts typically offer isolation and thermal
protection from winds. Carrion and easily scavenged prey provide
important sources of winter food in terrestrial habitats far from open
water.
The first major decline in the bald eagle population probably began
in the mid to late 1800s. Widespread shooting for feathers and trophies
led to extirpation of eagles in some areas. Shooting also reduced part
of the bald eagle's prey base. Populations of big game animals like
bison, which were seasonally important to eagles as carrion, were
severely reduced. Hunters also reduced the numbers of waterfowl,
shorebirds, and small mammals. Ranchers used carrion treated with
strychnine, thallium sulfate, and other poisons as bait to kill
livestock predators and ultimately killed many eagles as well. These
were the major factors, in addition to loss of nesting habitat from
forest clearing and development, which contributed to a reduction in
bald eagle numbers through the 1940s. In 1940, Congress passed the Bald
Eagle Protection Act (16 U.S.C. 668-668d). This law prohibits the take,
possession, sale, purchase, barter, or offer to sell, purchase or
barter, transport, export or import, of any bald eagle, alive or dead,
including any part, nest, or egg, unless allowed by
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permit (16 U.S.C. 668(a)). ``Take'' includes pursue, shoot, shoot at,
poison, wound, kill, capture, trap, collect, molest or disturb (16
U.S.C. 668c; 50 CFR 22.3). The Bald Eagle Protection Act and increased
public awareness of the bald eagle's status resulted in partial
recovery or at least a slower rate of decline of the species in most
areas of the country.
In the late 1940s, the use of dichloro-diphenyltrichloroethane
(DDT) and other organochlorine compounds became widespread. Initially,
DDT was sprayed extensively along coastal and other wetland areas to
control mosquitoes (Carson 1962, pp. 28-29, 45-55). Later farmers used
it as a general crop insecticide. As DDT accumulated in individual bald
eagles from ingesting prey containing DDT and its metabolites,
reproductive success plummeted. In the late 1960s and early 1970s, it
was determined that dichlorophenyl-dichloroethylene (DDE), the
principal breakdown product of DDT, accumulated in the fatty tissues of
adult female bald eagles. DDE impaired calcium release necessary for
normal eggshell formation, resulting in thin shells and reproductive
failure.
In response to this decline, the Secretary of the Interior, on
March 11, 1967 (32 FR 4001), listed bald eagles south of the 40th
parallel as endangered under the Endangered Species Preservation Act of
1966 (16 U.S.C. 668aa-668cc). Bald eagles north of this line were not
included in that action primarily because the Alaskan and Canadian
populations were not considered endangered in 1967. On December 31,
1972, the Environmental Protection Agency banned the use of DDT in the
United States. The following year, Congress passed the Endangered
Species Act of 1973 (16 U.S.C. 1531- 1544).
Nationwide bald eagle surveys, conducted in 1973 and 1974 by the
Service, other cooperating agencies, and conservation organizations,
revealed that the eagle population throughout the lower 48 States was
declining. The Service responded in 1978 by listing the bald eagle
throughout the lower 48 States as endangered except in Michigan,
Minnesota, Wisconsin, Washington, and Oregon, where it was designated
as threatened (43 FR 6233, February 14, 1978).
Between 1990 and 2000, the bald eagle population had a national
average productivity of at least one fledgling per nesting pair per
year. As a result, the bald eagle's nesting population increased at a
rate of about eight percent per year during this time period. Since
1963, when the Audubon Society estimated that there were 417 nesting
pairs, bald eagle breeding in the lower 48 States has expanded to more
than 9,789 nesting pairs (60 FR 36001, July 12, 1995; 64 FR 36457, July
6, 1999). By 2007, bald eagles bred in each of the lower 48 States,
with the greatest number of breeding pairs occurring in Minnesota
(1,313), Florida (1,133), Wisconsin (1,065), and Washington (848) (72
FR 37349, July 9, 2007).
Regional bald eagle populations in the Northwest, Great Lakes,
Chesapeake Bay, and Florida have increased five-fold from the late
1970s to the late 1990s. Bald eagles are now repopulating areas
throughout much of the species' historical range that were unoccupied
only a few years ago (64 FR 36454; July 6, 1999). The nationwide
recovery of the bald eagle is due in part to the reduction in levels of
persistent organochlorine pesticides (such as DDT) and habitat
protection and management actions.
Historical and Current Status of the Sonoran Desert Area Population and
Adjacent Areas
Below we present a discussion of eagle presence, nesting and
breeding productivity in the Sonoran Desert Area population and
throughout the entirety of each State surrounding the Sonoran Desert
Area population in order to provide context for our evaluation of
whether the Sonoran Desert Area is a distinct population segment of
bald eagles. As described above, the Sonoran Desert Area refers to all
Sonoran Desert bald eagle territories within Arizona, the Copper Basin
breeding area along the Colorado River just into California, and the
territories of interior Sonora, Mexico that occur within the Sonoran
Desert and adjacent transitional communities. Bald eagles in Baja
California are not included in our definition of the Sonoran Desert
Area population because: (1) They are associated with a marine, rather
than inland, environment (see Figure 1); (2) there is no documentation
of Baja bald eagles interchanging with those in the Sonoran Desert
Area; and (3) currently extant nests in Baja are limited to the
Magdalena Bay region along the coast of the Pacific Ocean (Arnaud et
al. 2001, p. 136; and King 2006, p. 4), in a coastal, rather than
inland, climate.
Arizona
Hunt et al. (1992, pp. A11-A12) summarized the earliest records
from the literature for bald eagles in Arizona. Coues noted bald eagles
in the vicinity of Fort Whipple (now Prescott) in 1866, and Henshaw
reported bald eagles south of Fort Apache in 1875. Bent (1937, pp. 321-
333) reported breeding eagles at Fort Whipple in 1866 and on the Salt
River Bird Reservation (since inundated by Roosevelt Lake) in 1911.
Breeding eagle information was also recorded in 1890 near Stoneman Lake
by S.A. Mearns. Additionally, there are reports of bald eagles along
rivers in the White Mountains from 1937, and reports of nesting bald
eagles along the Salt and Verde Rivers as early as 1930. Hunt et al.
(1992, pp. D41-D46, D291-D326, Figures D4.0-1, D5.0-1, F3, F4, and F5)
determined from reports and personal communications dating back to 1866
that historically there were 28 known breeding areas, 22 known and
probable nest sites, and at least 60 unverified reports of possible
nests/nest sites and unverified reports of bald eagles located across
the State of Arizona. Many of the 60 possible nests/nest sites reported
by Hunt et al. (1992) could be a collection of nests belonging to the
same breeding territory. These reported locations ranged to the
boundaries of the State from the Grand Canyon near Lake Powell, to the
lower Colorado River where it separates Arizona and California, to the
upper San Pedro River near the international border with Mexico, and
east near the boundary with New Mexico (Hunt et al. 1992, Figures D4.0-
1, D5.0-1, F3, F4, and F5).
More recent survey and monitoring efforts have increased our
knowledge of bald eagle distribution in Arizona (these data take into
account productivity for breeding areas throughout Arizona, and are not
restricted to the Sonoran Desert population of bald eagles evaluated
under the petition). The number of known breeding areas in Arizona in
1971 was 3; the number known in 2009 was 59. The number of bald eagle
pairs occupying these sites increased from 3 in 1971 to 48 in 2009. The
number of young hatched increased from a low of zero in 1972 to a high
of 55 in 2006 (Driscoll et al. 2006, pp. 48-49; McCarty and Johnson
2009, p. 8, in draft). Productivity has also changed at the bald eagle
breeding areas since the 1970s. Between 1975 and 1984, average annual
productivity was 0.95 young per occupied breeding area. Between 1987
and 2005, average annual productivity was 0.78 young per occupied
breeding area (derived from Table 7, pp. 48-50 in Driscoll et al.
2006).
Hunt et al. (1992, p. A155) conclude that it is likely that bald
eagles nested on rivers throughout the Southwest before habitat
modification occurred, as reports on the nature of river systems and
the assemblage of prey fishes both seem conducive to nesting success
and suggest ``richer and more extensive habitat in the lower desert''
than would have been available on the Mogollon
[[Page 25796]]
Plateau, where bald eagles are known to have occurred historically.
Recent reoccupation of some of these historical breeding areas by bald
eagles lends credibility to these reports. We evaluated a subset of the
Allison et al. (2008, pp. 17-18) data to determine the status of 43
breeding areas within the Sonoran Desert Area of Arizona and concluded
that 16 (37 percent) were pioneer breeding areas, or occupied for the
first time. An additional 27 (63 percent) were either reoccupied,
meaning they were known to have been occupied in the past, then
vacated, and subsequently reoccupied, or are considered to have been
existing before their discovery (Allison et al. 2008, pp. 15-16).
The Salt River Pima-Maricopa Indian Community states that the
O'odham have inhabited the Sonoran Desert and have known eagles since
``time immemorial'' (Anton and Garcia-Lewis 2009, p. 1). Although
anthropologists debate what this means, at least one noted
archaeologist has documented detailed evidence of cultural remains in
the nearby Pinacate area that date back more than 40,000 years (Hayden
and Dykinga 1988, p. XIV). A local, informal consensus of 10,000 years
is less controversial (Toupal 2003, p. 11). Bald eagles have been
documented historically within the culture of the Four Southern Tribes
of Arizona, which includes the Salt River Pima-Maricopa Indian
Community, Ak-Chin Indian Community, Gila River Indian Community, and
Tohono O'odham Nation (Anton and Garcia-Lewis 2009, p. 2). Because
eagles are considered to have equal or greater standing to humans,
eagle burials were carried out identical to human burial practices
(Anton and Garcia-Lewis 2009, p. 2), and bald eagle burials have been
recovered from archaeological sites ancestral to the O'odham culture.
In addition, eagles are extremely prominent in the O'odham song culture
(Anton and Garcia-Lewis 2009, p. 2). A paired set of songs recorded by
Underhill (1938, p. 109) for a Tohono O'odham eagle purification
ceremony recognized the bald eagle as the ``white-headed eagle.''
More recent evidence exists to demonstrate the importance and use
of bald eagles in Apache culture. Herrington et al. (1939, pp. 13-15)
noted the use of eagle feathers in religious practices and ceremonial
dances. The Apache Tribes have documented numerous artifacts that were
collected from the Tribes at Cibecue and East Fork/Whiteriver on the
White Mountain Apache Reservation and on the San Carlos Reservation
between 1901 and 1945. These Tribes note that these artifacts were
made, in part, with eagle feathers, and include hats or caps; shields;
medicine rings, shirts, and strings; amulets; war bonnets; armbands;
hair ornaments; and wooden figurines and crosses. The Tribes note that
these ceremonial items are of deep historical and ongoing importance,
such that they are actively pursuing their return from the museums to
the Tribes. The existence of these items demonstrates the use of eagle
feathers by the Tribes for at least the last 100 years (Apache Tribes
2009, Tabs 6-10).
Traditional ecological knowledge from the Apache tribes report more
breeding bald eagles 150 years ago than are present today.
Specifically, tribal representatives note that many areas that were
considered nesting sites on the San Carlos Apache Reservation such as
Warm Springs Canyon, Black River Canyon, and Salt Creek Canyon no
longer contain active bald eagle nests. Bald eagles are no longer found
at four out of seven areas that have Apache place-names that reference
bald eagles (Lupe et al. pers. comm. 2008, p. 4). The traditional
ecological knowledge shared by the Tribes at a July 2, 2008, meeting
indicates that historically more bald eagles were observed below
Coolidge Dam and at Talkalai Lake than currently exist.
Nevada
There are few historical or current breeding records for the State
of Nevada. The lone historical record describes bald eagles that nested
in a cave on an island at Pyramid Lake in northwestern Washoe County in
northwestern Nevada in 1866 (Service 1986, p. 7; Detrich 1986, p. 11;
S. Abele, Service, pers. comm. 2008a; 2008b). Over 100 years later, the
next verified nesting record occurred in 1985 along Salmon Falls Creek
in Elko County in northeastern Nevada near the Idaho border. More
modern nesting records are limited to approximately five breeding sites
associated with human-made water impoundments. Reproductive performance
and persistence of bald eagle pairs in Nevada has been varied. No
breeding has been observed at the Salmon Falls site since 1985.
Colorado
According to the Northern Bald Eagle Recovery Plan, bald eagles in
Colorado historically nested in the mountainous regions up to 10,000 ft
(3,048 m). Successful nesting records exist for nests found in
southwestern and west-central Colorado. Bald eagles were considered
common residents in the 1940s and 1950s in and around Rocky Mountain
National Park (Service 1983, p. 12). For southwestern Colorado, there
were no verified records of nesting bald eagles in the 1960s (Bailey
and Niedrach 1965 in Stahlecker and Brady 2004, p. 2). The first
confirmed record for southwestern Colorado occurred in 1974 at Electra
Lake (Winternitz 1998 in Stahlecker and Brady 2004, p. 2). In 1974, the
Colorado Division of Wildlife reported that only a single nesting pair
was known (Colorado Division of Wildlife 2008, p. 1). However, by 1981,
there were five known occupied bald eagle territories in the State of
Colorado (Service 1983, p. 23), and from the early 1980s to 2008, the
known bald eagle population increased to nearly 80 territories, of
which 60 are currently known to be active. Concentrations of breeding
eagles are found east of the Continental Divide within the South Platte
River watershed, on the Yampa River, on the White River, and on the
Colorado River. Greater than 40 territories are monitored annually,
with near 70 percent nest success, 1.19 young fledged per occupied
site, and 1.72 young fledged per successful site (Colorado Division of
Wildlife 2008, p. 1).
New Mexico
Available information indicates there was no specific, first-hand
information on bald eagles nesting anywhere in New Mexico prior to
1979. Unverified reports (Bailey 1928, p. 180; Ligon 1961, p. 75)
suggest one or two pairs may have nested in southwestern New Mexico, on
the upper Gila River and possibly the San Francisco River, prior to
1928. These second-hand reports lacked specifics and may have referred
to other species (Williams 2000, p. 1).
Since completion of the 1982 Recovery Plan, seven bald eagle
territories have been discovered, five in northern New Mexico in Colfax
and Rio Arriba Counties and two in southwestern New Mexico in Sierra
and Catron Counties. Four have been recently occupied, and productivity
has been fair with young produced in at least 6 to 15 years, depending
on the territory (H. Walker, New Mexico Department of Game and Fish,
pers. comm. 2008).
Southern California
Throughout southern California, historical bald eagle records are
known from the Channel Islands and mainland counties along the Pacific
Ocean (Detrich 1986, pp. 9-27). Prior to 1900, three bald eagle
territory records were known (Detrich 1986, pp. 10-13). From 1900 to
1940, reports of 24 to 60 nest
[[Page 25797]]
sites existed on islands off the coast of California, and are believed
to have been extirpated from the islands soon after 1958 (Detrich 1986,
pp. 18, 24). In inland areas in southern California, at least eight
bald eagle pairs were known from Santa Barbara, Ventura, Los Angeles,
Orange, and San Diego counties between 1900 and 1940, with indications
of presence prior to this timeframe (Detrich 1986, pp. 13-19). By 1981,
largely due to adverse changes to bald eagle habitat and the effects of
the pesticide DDT on reproduction, no breeding eagles were detected on
the southern California mainland (Detrich 1986, pp. 32, 33, 36, 39;
California Department of Fish and Game 2008, p. 2).
Beginning in 1980, bald eagles were translocated to Santa Catalina
Island as chicks or eggs from wild nests on the mainland, or from
captive breeding. Pairs of bald eagles have been breeding on the island
since 1987. In a subsequent relocation effort between 1987 and 1995 in
the central coast mountains of Monterey Bay, 66 eaglets were
translocated and released. A nesting pair first formed from those
releases in 1993, and there are currently three nesting pairs
(California Department of Fish and Game 2008, pp. 2-3). Releases of
birds occurred through 2000, with no releases conducted between 2002
and 2008 (Ventana Wildlife Society 2009, p. 1). Currently, there are
approximately six pairs of bald eagles on Catalina Island, with an
additional three pairs at Santa Cruz Island, and one pair at Santa Rosa
Island. There are approximately 35 to 40 bald eagles around the
Northern Channel islands, and another 20 birds around Catalina, for a
total of approximately 60 birds among the Channel Islands (A. Little,
pers. comm. 2008).
Presently, mainland southern California nesting bald eagles occur
at inland isolated manmade reservoirs. Bald eagle breeding sites can be
found in northwestern San Luis Obispo County (San Antonio and
Nacimiento Lakes), central Santa Barbara County (Lake Cachuma),
southwestern San Bernardino County (Silverwood Lake), extreme eastern
San Bernardino County near the Colorado River (Copper Basin Lake),
southwestern Riverside County (Hemet and Skinner Lakes), and central
San Diego County (Lake Henshaw) (AGFD 2008, California Department of
Fish and Game 2008, pp. 2-3; Driscoll and Mesta in prep. 2005, p. 110;
Ventana Wildlife Society 2008, p. 1). Nesting attempts at Silverwood
and Hemet Lakes are considered sporadic (Service 2005, p. 110). At
Skinner Lake, reproduction efforts in the mid-1990s were affected by
DDT, and the nest area subsequently burned down (Driscoll and Mesta in
prep. 2005; AGFD 2008). Nest sites in northwestern San Luis Obispo
County appear to be very productive, producing eaglets in all but one
year from 1993 to 2006 (Ventana Wildlife Society 2008, p. 7). For 2001
to 2008, two or three young have fledged annually from the Copper Basin
breeding area, with the exception of 2004 when the nest was blown down
(M. Melanson, Metropolitan Water District of Southern California, pers.
comm. 2006a, 2007, 2008). The blue aluminum leg bands of one of the
adult bald eagles at the Copper Basin site indicate that the bird
likely originated in Arizona (M. Melanson, Metropolitan Water District
of Southern California, pers. comm. 2006b).
Utah
Bald eagles were recorded as ``more or less frequent'' by Allen in
1871 (p. 164) in the vicinity of Ogden in northern Utah. Throughout
Utah, there are seven historical records between 1875 and 1928, with
five records of nesting bald eagles, and two other records of
nonbreeding bald eagle observations, all located between Great Salt
Lake and Utah Lake in northern Utah. In 1967, a nest was found to the
south in Wayne County at Bicknell, and in 1972, an additional nest was
located at Joes Valley Reservoir in San Pete County in central Utah,
but it has since fallen. Additional records from the 1970s were of
nests along the Colorado River at Westwater Canyon in 1975, and at the
head of Westwater Canyon between 1973 and 1977. Beginning in 1983,
nesting attempts occurred at three nesting territories in southeastern
Utah. Two of the territories were along the Colorado River near the
eastern border of Utah, with the third near Castle Dale in the center
of the State (Boschen 1995, pp. 7-8). Three known nest sites (Cisco,
Bitter Creek, and Castle Dale) were reported following survey work
completed in 1994. These three nest sites produced an average of
approximately 1.4 nestlings, with 1.05 successfully fledged between
1983 and 1994 (Boschen 1995, p. 103). Approximately 11 breeding areas
were known, considered active, and monitored between 1983 and 2005
(Darnell, Service, pers. comm. 2008).
West Texas
Historically, there were five nesting records for bald eagles in
Texas, and they were all west of the 100th Meridian in Texas. Lloyd
(1887, p. 189) reported nesting in Tom Green and Concho counties in
1886. Oberholser (1974, p. 246) and Boal (2006, p. 46) reported eggs
collected in Potter County near Amarillo by E.W. Gates in 1916.
Oberholser (1974, in Service 1982, p. 8) additionally reported eggs
collected by Smissen in 1890 in Scurry County south of Lubbock.
Oberholser also reported an undated sight record of breeding eagles in
Armstrong County near Amarillo. Kirby (pers. comm., in Service 1982)
reported an active nest in nearby Wheeler County in 1938, and indicated
it had been active for approximately 20 years. Throughout the 1980s and
early 1990s there were no known breeding bald eagles in western Texas
(Mabie et al. 1994, p. 215; Service 1982, p. 9). In 2004 and 2005, two
adult bald eagles and a nestling were observed at a nest in the
southern Great Plains of the Texas Panhandle. One young was produced in
2004, and two in 2005. No leg bands were readily observable on the
adult eagles (Boal et al. 2006, pp. 246-247).
Sonora, Mexico
Bald eagle territories were first recorded in Sonora, Mexico, along
the Rio Yaqui drainage in 1986 (Brown et al. 1986, pp. 7-14). Since
that time, seven bald eagle breeding areas have been verified, and they
were all located in the Sonoran Desert Area of Sonora (Brown et al.
1986, pp. 7-14; Brown et al. 1987b, pp. 1-2, 1987b, p. 279; Brown 1988,
p. 30; Brown and Olivera 1988, pp. 13-16; Brown et al. 1989, pp. 13-15;
Brown et al. 1990, pp. 7, 9; Mesta et al. 1993, pp. 8-12; Russell and
Monson 1998, pp. 62-63; Driscoll and Mesta 2005 in prep., pp. 78-90).
Four of these bald eagle breeding areas have remained occupied
(Driscoll and Mesta, in prep., pp. 78-90). However, reproductive
performance of these nests has been relatively poor. Only a single
nestling was recorded fledging in 2000 and 2001, and no successful
nests were observed in 1999, 2002, and 2005 (Driscoll and Mesta in
prep., p. 43). In 2008, no occupancy was detected at bald eagle
territories (R. Mesta, Service, pers. comm. 2008). A bald eagle pair
was observed in 2009; however, the previously used cliff nest is gone,
and a new nest was not confirmed. Illegal drug activity in the area has
increased human presence, making survey work difficult to accomplish.
The area is also affected by extensive water withdrawals, and drought
and dam operations, leaving the future of this site uncertain (R.
Mesta, Service, pers. comm. 2009).
[[Page 25798]]
Distinct Vertebrate Population Segment Analysis
Section 3(16) of the Act defines ``species'' to include ``any
species or subspecies of fish and wildlife or plants, and any distinct
population segment of any species of vertebrate fish or wildlife which
interbreeds when mature'' (16 U.S.C. 1532(16)). To interpret and
implement the distinct vertebrate population segment provisions of the
Act and congressional guidance, the Service and the National Marine
Fisheries Service (now the National Oceanic and Atmospheric
Administration--Fisheries Service), published the Policy Regarding the
Recognition of Distinct Vertebrate Population Segments (DPS Policy) in
the Federal Register on February 7, 1996 (61 FR 4722). The DPS Policy
sets forth a three-step process: the Policy requires the Service first
to determine whether a vertebrate population is discrete and, if the
population is discrete, then to determine whether the population is
significant. Lastly, if the population is determined to be both
discrete and significant, then the DPS Policy requires the Service to
evaluate the conservation status of the population to determine whether
the DPS falls within the Section 3(16) definition of an ``endangered
species'' or ``threatened species.''
In accordance with our DPS Policy, this section details our
analysis of whether the vertebrate population segment under
consideration for listing qualifies as a DPS, specifically, whether:
(1) The population segment is discrete from the remainder of the
species to which it belongs: and (2) the population is significant to
the species to which it belongs. Discreteness refers to the ability to
delineate a population segment from other members of a taxon based on
either: (1) Physical, physiological, ecological, or behavioral factors;
or (2) international boundaries that result in significant differences
in control of exploitation, management, or habitat conservation status,
or regulatory mechanisms that are significant in light of section
4(a)(1)(B) of the Act.
Under our DPS Policy, if we have determined that a population
segment is discrete under one or more of the discreteness conditions,
we consider its significance to the larger taxon to which it belongs in
light of Congressional guidance (see Senate Report 151, 96th Congress,
1st Session) that the authority to list DPSs be used ``sparingly''
while encouraging the conservation of genetic diversity. In carrying
out this examination, we consider available scientific evidence of the
population's importance to the taxon to which it belongs. This
consideration may include, but is not limited to, the following
categories of information: (1) The persistence of the population
segment in an ecological setting that is unusual or unique for the
taxon; (2) evidence that loss of the population segment would result in
a significant gap in the range of the taxon; (3) evidence that the
population segment represents the only surviving natural occurrence of
a taxon that may be more abundant elsewhere as an introduced population
outside of its historical range; and (4) evidence that the discrete
population segment differs markedly from other populations of the
species in its genetic characteristics.
The first step in our DPS analysis was to identify the boundaries
of the potential population--that is, the areas where the population we
are evaluating occurs. The petition from CBD, the Maricopa Audubon
Society, and the Arizona Audubon Council requested listing for the
``Southwestern desert nesting bald eagle population.''
Determination of the Area for Analysis
The March 6, 2008, court order directed the Service to conduct a
status review of the ``Desert bald eagle population.'' The population
referenced in the court order consists of those bald eagles in the
Sonoran Desert of the Southwest that reside in central Arizona and
northwestern Mexico. While we had specific information from the
petitioner with respect to elevational parameters, bald eagle breeding
areas, the Upper and Lower Sonoran Life Zones, and the State of
Arizona, ambiguity remained with respect to where the boundaries of
``central Arizona'' are and which transition areas outside of the Upper
and Lower Sonoran Life Zones to include. Because of these ambiguities
and lack of a specific map in the petition, we were left to interpret
them, primarily at the perimeters of those areas.
In responding to the 2008 court order, we published a rule on May
1, 2008, reinstating threatened status under the Act to the bald eagle
in the Sonoran Desert Area of central Arizona in eight Arizona
counties: (1) Yavapai, Gila, Graham, Pinal, and Maricopa Counties in
their entirety; and (2) southern Mohave County (that portion south and
east of the centerline of Interstate Highway 40 and east of Arizona
Highway 95), eastern LaPaz County (that portion east of the centerline
of U.S. and Arizona Highways 95), and northern Yuma County (that
portion east of the centerline of U.S. Highway 95 and north of the
centerline of Interstate Highway 8). We limited the reinstatement of
threatened status to these areas because Sonoran Desert bald eagles
were only listed under the Act in Arizona (and not in Mexico) at the
time of the petition. Therefore, the court's order enjoining our final
delisting decision applied only to those eagles that reside in the
Sonoran Desert of central Arizona.
For the February 25, 2010, status review, we revisited the issue of
where the population we are evaluating occurs, based on a more in-depth
review of information received from the public, Tribes, and information
in our files at that time. We determined that an appropriate
delineation for the analysis includes all Sonoran Desert bald eagle
territories within Arizona, the Copper Basin breeding area along the
Colorado River just into California, and the territories of Sonora,
Mexico, that occur within the Sonoran Desert and adjacent transitional
communities. This expanded boundary was developed using vegetation
community boundaries, elevation, and breeding bald eagle movement. This
interpretation combines geographic proximity and recognized Sonoran
Desert vegetation and transition life zones. We determined the
transition areas based on our knowledge of their proximity to the
Sonoran Desert itself, excluding territories more properly classified
as montane or grassland habitat. Bald eagles in Baja California,
Mexico, occur in an area where the Sonoran Desert vegetation community
abuts a coastal environment. We excluded bald eagles in this area
because they depend on marine resources rather than inland fisheries.
We based delineation of the potential DPS on the best available
scientific information, including the parameters provided by CBD (i.e.,
bald eagle territories, elevation, life zones, and transition areas),
and the resulting expanded area for the population includes known bald
eagle breeding areas within the Sonoran Desert vegetation community and
transition areas, as defined by Brown (1994, pp. 181-221), except Baja
California.
As noted above, we included Sonoran desert bald eagle territories
in Sonora, Mexico, as part of the potential DPS because that area has
the same vegetation and climate as the Sonoran Desert areas in Arizona.
Bald eagles in Sonora use Sonoran Desert and transition vegetation
communities as do bald eagles in the Sonoran Desert areas of Arizona
and southern California. In addition, breeding season chronology in
both areas appears to be similar (Driscoll et al. 2005 in prep., pp.
31-32),
[[Page 25799]]
occurring between December and June. Bald eagles in Sonora also nest in
riparian trees and cliffs, as they do in Arizona (Driscoll et al. 2005
in prep., p. 31).
When based strictly on vegetation or elevation lines, the expanded
area where the population occurs is irregular and complex, and would be
difficult to interpret. For this reason, we delineated the area of the
population with more easily identifiable road, county, and state lines.
Boundaries of the Potential DPS
In analyzing the potential DPS under this 12-month status review,
we considered habitat use by bald eagles breeding in the southwestern
United States and Sonoran Desert areas in Mexico, vegetation
communities in which breeding areas occur, and elevation levels at
which breeding areas occur, as we did at the 90-day petition finding
stage. However, we have reevaluated all potential areas that may meet
the criteria described below, including areas considered in the 90-day
finding. As a result, in this review, we did not restrict the potential
DPS to the State of Arizona, and have instead expanded the area covered
by our previous analysis so that this analysis includes portions of
southeastern California along the Colorado River, Arizona, and Sonora,
Mexico. We now refer to this expanded potential DPS area as the
``Sonoran Desert Area population,'' which replaces the term ``Sonoran
Desert Area of central Arizona,'' as described in our May 1, 2008,
Federal Register rule (73 FR 23966) listing the Sonoran Desert bald
eagle as threatened.
To determine which areas should be included within the expanded
boundary for the Sonoran Desert Area, we considered three factors: (1)
The Sonoran Desert vegetation community (Brown 1994, pp. 180-221; Brown
and Lowe 1994, map); (2) an elevational range for known breeding areas
within the Sonoran Desert (excluding Baja California); and (3) movement
patterns of breeding bald eagles both into and out of the Sonoran
Desert Area. We included within the boundary portions of the Sonoran
Desert, including its subdivisions and ``transition areas.''
Subdivisions of the Sonoran Desert include the Lower Colorado River
Valley, Arizona Upland, Vizcaino, Central Gulf Coast, Plains of Sonora,
and Magdalena (Brown 1994, pp. 190-221). Transition areas are those
vegetation communities adjacent to the Sonoran Desert community. Brown
(1994, p. 181) includes as transition areas semidesert grasslands,
Sinaloan thornscrub, and chaparral. The majority of the breeding areas
within the boundary occur in the Arizona Upland Subdivision of the
Sonoran Desert. Exceptions include those breeding areas in the
transition communities (where 14 of 61 breeding areas are located) of
Interior Chaparral, Plains & Great Basin Grassland, Semidesert
Grassland, and Sinaloan Thornscrub (Brown 1994). These communities are
most often adjacent to the Arizona Upland Subdivision of the Sonoran
Desert, where bald eagles in these areas forage at least partially
within the desertscrub.
We also based the boundary on those portions of the Southwest
within the elevational range of 984 to 5,643 ft (300 to 1,720 m). This
elevational range encompasses all known bald eagle breeding areas
within the Sonoran Desert in the United States and Sonora, Mexico.
Using Geographic Information Systems, the appropriate elevational
ranges were overlapped with the Sonoran Desert vegetation community to
determine where both criteria were met.
We also considered information on movement of bald eagles into and
out of the Sonoran Desert, as determined through banding and monitoring
information. Specifically, we included within the boundary those bald
eagles known to originate in or breed in the Sonoran Desert and
transition areas, excluding Baja California. The banding and monitoring
information used to determine eagles originating or breeding in the
Sonoran Desert Area is described in detail below.
Figure 1 below illustrates the boundary developed based on
vegetation community, elevation, and breeding bald eagle movement. The
boundary was modified from following strictly elevational or vegetation
lines to follow more easily identifiable road, county, and state lines.
BILLING CODE 4310-55-P
[[Page 25800]]
[GRAPHIC] [TIFF OMITTED] TP01MY12.000
BILLING CODE 4310-55-C
The northern perimeter of the expanded potential DPS boundary in
Arizona is the same as the potential DPS boundary that we used in our
May 1, 2008, Federal Register notice (73 FR 23966). This boundary
follows the southern edges of Coconino and Navajo Counties, and
portions of Apache County. It follows the Graham County line south on
the east side until it reaches the Cochise County boundary.
On the west, the boundary drops south along the Mohave-Yavapai
boundary until it reaches Interstate 40. The boundary then follows
Interstate 40 west until its intersection with the State boundary. It
continues west 5 miles (mi) (8 kilometers (km)) and then south along a
line drawn 5 mi (8 km) west of and parallel to the Colorado River until
it reaches Highway 2 in Sonora, Mexico.
The southern boundary of the expanded potential DPS follows Highway
2 in Mexico east until its intersection with Highway 15. It follows
Highway 15 until its intersection with
[[Page 25801]]
Highway 16. The southern boundary continues along Highway 16 until it
reaches the State boundary between Sonora and Chihuahua. The eastern
boundary of the expanded potential DPS follows the State line between
Sonora and Chihuahua north until it reaches the international boundary
between the United States and Mexico at New Mexico, and continues west
to the State boundary between Arizona and New Mexico. The eastern
boundary then continues north along Cochise County, turning slightly
west along the northern edge of Cochise County before rejoining the
northern perimeter.
Bald eagles within the boundary that constitutes the expanded area
for the potential DPS include those that occur within the appropriate
vegetation communities and elevational range. It therefore includes the
breeding area located in southeastern California, because it is within
the Lower Colorado River subdivision of the Sonoran Desert. In
addition, the bald eagles at that breeding area originated at the
Horseshoe Breeding Area in Arizona. We have included part of Sonora,
Mexico, within the expanded area for the potential DPS because bald
eagles occur in Sonoran Desert and transitional communities there, as
do those in Arizona and California. As discussed above, we have
excluded from the expanded potential DPS bald eagles occurring in Baja
California, Mexico, because that area is associated with a marine,
rather than inland, environment.
Arizona has additional bald eagle breeding areas outside of the
expanded potential DPS boundary. These breeding areas include Canyon de
Chelly, Luna, Becker, Crescent, Greer, Woods Canyon, and Lower Lake
Mary. These breeding areas were excluded because they are not located
within the Sonoran Desert.
Discreteness
Under the DPS Policy, a population segment of a vertebrate taxon
may be considered discrete if it satisfies either one of the following
conditions:
(1) It is markedly separated from other populations of the same
taxon as a consequence of physical, physiological, ecological, or
behavioral factors. Quantitative measures of genetic or morphological
discontinuity may provide evidence of this separation.
(2) It is delimited by international governmental boundaries within
which differences in control of exploitation, management of habitat,
conservation status, or regulatory mechanisms exist that are
significant in light of section 4(a)(1)(D) of the Act.
Banding and Monitoring Information
Bird banding and resighting are important tools used to answer
questions regarding the biology and movement of individual birds (U.S.
Geological Survey 2008, p. 1). The techniques used on bald eagles in
the Southwest are consistent with marking technique standards (Varland
et al. 2007, pp. 222-228). Within this analysis, we use banding and
resighting data for bald eagles to determine if bald eagles in the
Sonoran Desert Area are markedly separate from other breeding
populations of bald eagles. Specifically, we use banding and resighting
data to determine if bald eagles originating in areas outside the
Sonoran Desert Area have moved into the Sonoran Desert Area to breed
(immigration), or if bald eagles originating in the Sonoran Desert Area
have moved out of the Sonoran Desert Area to breed (emigration).
We used bald eagle banding and resighting information collected
between 1987 and 2007 as this is the time period during which banding
and resighting efforts were most thorough in the Southwest. Banding of
bald eagle nestlings began prior to this time in Arizona, starting in
approximately 1977, and multiple researchers contributed to early
banding efforts (Hildebrandt and Ohmart 1978; Haywood and Ohmart 1980,
1981, 1982, 1983; Grubb 1986), as summarized in Hunt et al. 1992 (pp.
C181-C202). However, early banding efforts were opportunistic, and the
bands used at that time were difficult to read without capturing birds
or recovering dead birds. As a result, little resight information was
gained. Beginning in 1987, biologists increased efforts to band all
nestlings and improved the effectiveness of banding and resighting by
using color visual identification bands, which are more easily
identified (Hunt et al. 1992, pp. C181-C202; Driscoll et al. 2006, p.
26). In total, the banding and resighting effort for bald eagles in
Arizona has continued for 30 years with the last 20 years using the
more informative color bands.
To determine the movement of breeding bald eagles in our target
time period of 1987 to 2007, we relied on data from two datasets. The
first dataset, called the Bird Banding Lab (BBL) dataset, is derived
from data collected and collated by the U.S. Geological Survey Bird
Banding Laboratory (U.S. Geological Survey 2008). The BBL dataset
consists of over 19,000 records for bald eagles throughout the species'
range, including those banded in the Southwest. The second dataset,
called the AGFD dataset, is derived from data compiled and used by
Allison et al. (2008) in a demographic analysis for bald eagles in
Arizona.
Because our analysis focused on determining whether or not there is
immigration or emigration of bald eagles to and from the Sonoran Desert
Area, we analyzed bald eagles banded as nestlings and resighted as
adults. Using only those birds banded as nestlings ensures that the
origin of the banded birds is known, and that young birds originating
in other areas are not included in the analysis. Using only resight
information for breeding bald eagles eliminates data associated with
juvenile migrants, which would not contribute to the breeding
population. Generally, age five is accepted as the age at which adult
bald eagles breed throughout most of the species' range. For this
reason, when evaluating the nationwide BBL dataset, we considered bald
eagles 5 years of age or older as breeding adults. However, for the
AGFD dataset, where there are numerous instances of bald eagles
breeding at 4 years of age in Arizona (Allison et al. 2008), we
considered bald eagles 4 years of age or older as breeding adults.
Immigration Into the Sonoran Desert Area
For purposes of this analysis, immigration is defined as the
movement of individuals that were banded as nestlings outside of the
Sonoran Desert Area and then are subsequently resighted as breeding
birds inside the Sonoran Desert Area. In our analysis of the likelihood
of bald eagle immigration into the Sonoran Desert Area from areas in
closest proximity to the Sonoran Desert Area, we used data from the
AGFD and the broader BBL dataset and considered bald eagle banding and
resighting information from the States in proximity to the Sonoran
Desert Area, including California, Colorado, Nevada, New Mexico, Texas,
and Utah, as well as birds in Arizona but outside of the Sonoran Desert
Area (see Table 1).
[[Page 25802]]
Table 1--Records for Bald Eagles Banded as Nestlings in Areas Outside the Sonoran Desert Area and Resighted as
Breeding Birds From 1987 to 2007
[U.S. Geological Survey 2008; K. McCarty, AGFD, pers. comm. 2009; Driscoll et al. 2006, p. 49]
----------------------------------------------------------------------------------------------------------------
Number of
nestlings Number of
banded in banded Number of
areas in close nestlings States where banded resightings in
State where banded proximity to resighted as eagles were resighted the Sonoran
the Sonoran breeding birds Desert area
Desert area 1987-2007
1987-2002
----------------------------------------------------------------------------------------------------------------
Arizona outside the Sonoran Desert 12 0 ........................ 0
Area.
California............................ 103 13 (12.6%) British Columbia, CA, WA 0
Colorado.............................. 152 7 (4.6%) CO, WY.................. 0
Nevada................................ 0 0 (0%) ........................ 0
New Mexico............................ 0 0 (0%) ........................ 0
Texas................................. 64 5 (7.8%) AZ, CA, NE, NM, TX...... 0
Utah.................................. 6 0 (0%) UT...................... 0
-------------------------------- ---------------
Total............................. 337 25 (7.4%) ........................ 0
----------------------------------------------------------------------------------------------------------------
Available data from 2008 are not as thorough, but they are consistent with the findings from the data reported.
Further, the Texas bird resighted in Arizona occurs at a high-elevation nest outside of the Sonoran Desert
Area. Note: We know of no banding information for birds banded in Mexico outside the Sonoran Desert Area.
Using the AGFD dataset, Allison et al. (2008, p. 25) indicate that
anticipated survival rates for fledglings to age four is 28 percent. It
should be noted that the mortality rates derived by Allison et al.
(2008, p. 4) are based on modeling; however, the model was based on
data collected over a 10-year period from 1993 to 2003.
The information summarized in Table 1 indicates that 337 bald
eagles were banded as nestlings between 1987 and 2002 (the latest year
for which a banded cohort could reach 5 years of age by 2007) in the
areas outside of but in proximity to the Sonoran Desert Area. Applying
the survival rate of 28 percent to the 337 bald eagles reported banded
as nestlings in Table 1, we would anticipate that approximately 94
nestlings would have survived to age four. Only 25 of the banded
nestlings were resighted as breeding birds, and the fate of the
remaining 69 nestlings is unknown. However, none of the 25 banded
nestlings were resighted as breeding birds within the Sonoran Desert
Area (see Table 1).
While the number of banded and resighted birds in Table 1 is small,
given the intensive effort in Arizona to identify the origins of banded
breeding birds, we believe some inference is possible suggesting that
the probability of nestlings originating outside of the Sonoran Desert
Area and immigrating into the Sonoran Desert Area to breed is low.
There is no known immigration from the Canyon de Chelly, Lower Lake
Mary, Becker, Woods Canyon, Crescent, Greer, and Luna Lake breeding
areas located at higher elevations within Arizona outside of the
Sonoran Desert Area. To date, 29 nestlings produced at these breeding
areas have been banded. Twenty-five of these were banded at the Luna
breeding area during 1994-2000, 2002-2005, and 2007, with 22 of them
fledging successfully (K. McCarty, AGFD, pers. comm. 2009). As of 2008,
none of these banded offspring are known to have entered the breeding
population of bald eagles in the Sonoran Desert Area (AGFD 2008a, pp.
1-2). The male bird at the Crescent breeding area is from the Luna
breeding area (the female is unbanded) (Jacobson et al. 2004, p. 16).
Similarly, the male bird at the Greer breeding area is from the Luna
breeding area, and the female is unbanded (McCarty and Jacobson 2008,
p. 9). Lower Lake Mary fledged four young in 2005 and 2006, and the
young were banded. The Woods Canyon and Greer breeding areas were first
detected in 2008, and no young fledged that year from either breeding
area. Six young have successfully fledged from Canyon de Chelly as of
this date, none of which were banded (AGFD 2006, pp. 1-2; AGFD 2007,
pp. 1-2; Jacobson et al. 2007, pp. 16-19; AGFD 2008a, pp. 48-49; AGFD
2008, unpubl. data; AGFD 2009, pp. 1-2).
Biologists, primarily R. Mesta, estimate that, due to difficulty in
accessing territories in Sonora, Mexico, they are able to monitor
approximately 40 to 60 percent of the known nest sites each year, and
20 to 30 percent of the known birds are observed while visiting these
territories. Approximately 80 percent of the birds detected have been
examined for auxiliary markers, such as colored bands, and biologists
believe that if marked bald eagles were occupying known territories
after 1990, they would likely have been detected. However, they note
that, in years in which surveys are conducted, breeding areas are
visited only once and for a short period of time, which would make it
easy to miss an individual eagle. They note that, in 1992, an adult at
the Fig Tree breeding area had a yellow wing tag (potentially
indicating it had originated in Texas or Florida) that could not be
read, but no one has observed the bird since ((Driscoll and Mesta 2005,
in prep., p. 62; R. Mesta, Service, pers. comm. 2008, Ortego et al.
2009, p. 10).
Emigration From the Sonoran Desert Area
Emigration is defined here as the movement of individuals
originating in the Sonoran Desert Area to areas outside the Sonoran
Desert Area where they are resighted as birds of breeding age. Our
analysis of data from the BBL dataset found that 41 of the 42 nestlings
(97.6 percent) banded within the Arizona portion of the Sonoran Desert
Area were subsequently resighted within the Sonoran Desert Area. Only
one eagle (2.4 percent) of breeding age was resighted outside of the
Sonoran Desert Area, near Temecula, California (see Table 2). The BBL
dataset shows that there were 371 bald eagles banded in Arizona between
1987 and 2007. With anticipated survival rates from fledgling to 4
years of age at 28 percent, we estimate that approximately 104
nestlings should have survived to age four. While we know that 42 were
resighted, the fate of the remaining 62 birds is unknown.
[[Page 25803]]
Table 2--Bald Eagles Banded in Arizona Between 1987 and 2002 and
Recaptured or Resighted as Birds of Breeding Age
[U.S. Geological Survey 2008]
------------------------------------------------------------------------
Number of
State birds (percent Notes
recovered)
------------------------------------------------------------------------
Within the Sonoran Desert Area:
Arizona.................... 40 (95.2%) .......................
Sonora, Mexico............. 1 (2.4%) Records indicate this
bird was an adult
entangled in fishing
line at El Novillo
Reservoir in Sonora.
There was no breeding
area at the reservoir,
and the bird was not
subsequently detected
at a breeding area.
----------------
Subtotal................... 41 (97.6%) .......................
----------------
Outside of the Sonoran Desert
Area:
California................. 1 (2.4%) This bird established a
breeding area in
California near
Temecula. Birds in
this breeding area
were not successful in
reproducing, and the
nest site subsequently
burned down (AGFD
2008a, p. 6).
Colorado................... 0 (0%) .......................
Nevada..................... 0 (0%) .......................
New Mexico................. 0 (0%) .......................
Oklahoma................... 0 (0%) .......................
Texas...................... 0 (0%) .......................
Utah....................... 0 (0%) .......................
----------------
Subtotal................... 1 (2.4%) .......................
----------------
Total.................. 42 (100%) .......................
------------------------------------------------------------------------
With respect to emigration, data in the AGFD dataset, a separate
dataset from the BBL discussed above, illustrate the fate of 89 of 314
nestlings banded within the Sonoran Desert Area. Only 1 of the 89 birds
was documented breeding outside the Sonoran Desert Area. Fifty returned
to breed in the Sonoran Desert Area, 1 bred (unsuccessfully) in
California, and 38 were known to have died before breeding (see Table
3) (Allison et al. 2008, p. 19). Allison et al. (2008, p. 7) note that,
from 1987 through 2003, 83 percent of known fledglings in the Sonoran
Desert Area were banded. Traditional ecological knowledge about bald
eagles supports these data on emigration. Western Apache informants
having expert knowledge of bald eagles in the Sonoran Desert Area
testified that adult eagles do not leave Arizona.
Table 3--Disposition of Arizona Bald Eagles Banded as Nestlings From
1987 to 2003
[Allison et al. 2008, p. 19]
------------------------------------------------------------------------
Number of
Fate of nestlings eagles
------------------------------------------------------------------------
Dead before fledging.................................... 123
Unbanded Nestlings...................................... 62
Banded Nestlings--Fate Unknown.......................... 225
Banded Nestlings--Fate Known:
Dead before Breeding.................................. 38
Bred in Arizona....................................... 50
Bred in California.................................... 1
---------------
Total............................................. 499
------------------------------------------------------------------------
Banding and resighting efforts have not been as intensive in the
areas in close proximity to the Sonoran Desert Area as they have been
in Arizona, including the Sonoran Desert Area. We sent a questionnaire
to bald eagle biologists in surrounding States in 2008 in an attempt to
determine the level of banding and monitoring efforts in some of these
regions. In response to the questionnaire, we determined that surveys
for breeding birds occur annually at Santa Cruz and Santa Rosa Islands
off the coast of California, as well as in southern California at Lake
Hemet. In survey efforts for these areas, all known territories and 100
percent of the known birds are visited, and no birds have bands or
markers from Arizona (Hoggan 2008, pp. 1-2; P. Sharpe, pers. comm.
2008). Additionally, less-formal monitoring occurs in other areas in
California through a variety of agencies and interested groups,
including the U.S. Forest Service, the California Department of Fish
and Game, the Ventana Wildlife Society, and the Channel Islands Live!
Web site with similar results (i.e., no birds with bands from Arizona
have been reported). In addition, sites known to support breeding
pairs, such as the Copper Basin site, are monitored regularly.
Six New Mexico territories have been monitored closely since their
discovery in 1979, with no bands or markers from Arizona observed (S.
Williams, pers. comm. 2008). Since 1974, the Colorado Division of
Wildlife has monitored nesting activity; State personnel currently
monitor approximately 40 of their 80 nests each year and band eaglets
at approximately one-third of those nests (Colorado Division of
Wildlife 2008, p. 1). No bands or markers from Arizona were observed.
We have received no data for Utah or Nevada. Information on bald
eagles banded within Arizona but outside the Sonoran Desert Area is
summarized above under the ``Immigration into the Sonoran Desert Area''
discussion above.
The data from areas in close proximity to the Sonoran Desert Area
are not as thorough as those collected in
[[Page 25804]]
Arizona, including in the Sonoran Desert Area. However, the banding and
monitoring effort for breeding bald eagles in Arizona over a 30-year
period has revealed only one breeding bird to date that immigrated into
Arizona (Luna Lake, outside the Sonoran Desert Area). We anticipate
that, if immigration is occurring at such a low level, the same could
be true of emigration as there are no known barriers that would favor
emigration over immigration.
Conclusion on Banding Data
We find that the data on banding and resighting, while not
extensive for areas in proximity to the Sonoran Desert Area, are
collectively sufficient to document that bald eagles in the Sonoran
Desert Area experience limited or rare reproductive interchange with
bald eagles outside the Sonoran Desert Area. Bald eagle banding and
resighting studies have been ongoing for greater than 30 years in
Arizona, with the last 20 years using the more informative color bands.
As reported in the BBL dataset, of the 79 nestlings banded in Arizona
and later resighted, 1 emigrated to California, outside of the Sonoran
Desert Area, and never successfully reproduced. This finding indicates
that 97.6 percent of the bald eagles banded and resighted as breeding
birds originated and returned to breed in the Sonoran Desert Area, with
only 2.4 percent (one bird) of breeding birds resighted in other areas
(Table 2). Similarly, the AGFD dataset indicates that, for the
nestlings banded between 1987 and 2003 in areas outside of but in close
proximity to the Sonoran Desert Area and resighted as breeding birds,
none have immigrated to breed in the Sonoran Desert Area.
While it is not possible to band and resight all bald eagles as
breeding birds, the information provided suggests that the majority of
breeding bald eagles within the Sonoran Desert Area population
originated in the Sonoran Desert Area population, and have not been
known to emigrate elsewhere to become part of a breeding population.
Data have been collected over a substantial time period under this
effort, during which only one instance of a possible immigration and
only one instance of emigration have been observed within the Sonoran
Desert Area. We believe it is reasonable to conclude that in rare
instances, immigration or emigration of an occasional bald eagle may
occur; however, we consider the results from this 20-year period
sufficient to document a marked separation of breeding populations. Our
DPS Policy does not require complete isolation, and allows for some
limited interchange among population segments considered to be discrete
(61 FR 4722; February 7, 1996). Based on the results of these banding
and resighting data in Arizona and in neighboring States, we conclude
that the Sonoran Desert Area bald eagles are not interbreeding with
other populations, although some intermixing may occur at a very small
rate. We conclude that the best scientific data available indicates a
marked separation of Sonoran Desert Area bald eagles from bald eagles
outside of the Sonoran Desert Area.
Natal Dispersal and Fidelity
Bald eagles are known to return close to their place of birth to
breed (Stalmaster 1987, p. 41). To illustrate the potential for
breeding bird exchange between populations, the Service examined the
records of bald eagles that were banded as nestlings and recovered 5 or
more years later at breeding age. We analyzed data associated with the
eagles in the lower 48 States to derive a median dispersal distance of
43 mi (69 km) from their natal site to their breeding area. Known
nesting sites were then buffered by 43 mi (69 km) to determine the
amount of breeding bird exchange that typically occurs (Service 2008,
pp. 17-18). Based on this analysis, Sonoran Desert Area bald eagles in
the United States are separated from other southwestern populations by
distances exceeding the median dispersal distance of 43 mi (69 km) for
the species. The higher-elevation breeding areas in Arizona are an
exception to this separation, as they are less than 43 mi (69 km) from
Sonoran Desert Area bald eagles; however, we believe these birds to be
reproductively and markedly separate from Sonoran Desert Area bald
eagles, as described in the discussions on immigration above, because
no banded offspring from these higher-elevation areas have been known
to enter the breeding population of bald eagles in the Sonoran Desert
Area.
Observations of actual dispersal behavior support the same
conclusion as that derived from the modeling exercise discussed above.
Hunt et al. (1992, p. A144) surveyed biologists studying nine bald
eagle populations throughout North America, consisting of more than
2,000 breeding pairs of bald eagles. Of those breeding pairs, only two
adults were observed to breed outside of their natal area. Mabie et al.
(1994, p. 218) similarly concluded through their study in Texas and the
Greater Yellowstone ecosystem that bald eagles tend to breed near their
natal area. Gerrard et al. (1992, pp. 159, 164) observed four marked
adults in Saskatchewan, Canada, and determined that they bred within
15.5 mi (25 km) of their natal territory.
Natal dispersal patterns for Sonoran Desert Area bald eagles are
similar to those in the studies discussed above. Data from 21 female
and 35 male bald eagles in Arizona indicate that adult females
dispersed an average of 68.1 mi (109.7 km) from their natal areas,
while males dispersed an average of 28.0 mi (45.1 km) from their natal
areas to breed (Allison et al. 2008, p. 30), but remained within the
Sonoran Desert Area.
This information about natal dispersal patterns supports our
conclusion above, based on the banding and monitoring data, that there
is a marked separation of Sonoran Desert Area bald eagles from bald
eagles outside of the Sonoran Desert Area.
Lack of Population Sources
The immigration of adult bald eagles into the Sonoran Desert Area
population from populations in relatively close proximity to the
Sonoran Desert Area is likely limited by small population sizes in
surrounding States, and their separation from the Sonoran Desert Area
by long distances, over unoccupied habitats. There are currently eight
known breeding areas in southern California in addition to populations
on Santa Cruz and Santa Rosa Islands off the coast of California
(California Department of Fish and Game 2008, pp. 2-3; Ventana Wildlife
Society 2008, p. 1). Colorado has a somewhat larger population, with
approximately 80 active breeding areas (Colorado Division of Wildlife
2008, p. 1). Nevada has approximately one inactive and five active
breeding territories. Two territories, Carson River and Lahontan
Reservoir, last had eagles detected in 2002 and 2006, respectively. The
occupancy of two others is not yet confirmed. The remaining breeding
area produced only two young from 1996 to 2007 (K. Kritz, Service,
pers. comm. 2008). Utah has approximately 10 active territories and one
inactive breeding territory (N. Darnall, Service, pers. comm. 2008).
For New Mexico, the population of bald eagles consists of four
currently occupied territories (H. Walker, NMDGF, pers. comm. 2009).
West Texas currently has one active breeding territory west of the
100th Meridian. This territory has been active since 1994 (C. Boal,
pers. comm. 2009).
Marked Separation as a Consequence of Ecological Factors
A final factor markedly separating Sonoran Desert Area bald eagles
is the unsuitability of habitat in areas surrounding the Sonoran Desert
Area for
[[Page 25805]]
occupancy by breeding birds. The majority of the bald eagle population
in the Sonoran Desert Area occurs in central Arizona within the
riparian areas of the Sonoran Desert as described in Brown (1994, pp.
180-221) and adjacent vegetation communities. Across the western United
States, there are large geographic areas where breeding bald eagles are
rarely found. These areas are associated with the Great Basin and
Mohave Deserts, indicating that conditions in these desert biotic
communities are not suitable for occupancy. In contrast, the Sonoran
Desert and its subdivisions, where nesting bald eagles within the
Sonoran Desert Area are located, are suitable for breeding areas
because of the availability of water, prey, and trees suitable for
nesting and perching. The Sonoran Desert scrub vegetation community is
unique from other desert scrub formations in North America in its
tropical and subtropical influences. Within the community, the riparian
or riverine habitat occupied by breeding bald eagles is limited to
areas where there is sufficient winter precipitation to support
vegetation along streams (Brown 1994, p. 269).
Western Apache traditional ecological knowledge corroborates these
data regarding bald eagles within the Sonoran Desert Area being
ecologically separated from other populations. Three Apache place names
use the term Itsa Bigow (``bald eagle's home''). Apaches use the term
gowa (meaning ``home'') referring to the eagle's entire habitat, as
opposed to the term bit'oh (``its nest''). According to Basso (1996),
the Western Apaches' perception of the land works in specific ways to
influence Apaches' awareness of themselves. The process of ``place
naming'' documents where and how Apaches learned about the environment
and how they incorporated these names into social and environmental
ethics (Basso 1996). This concept is further exemplified by the Apache
word ``ni''; this expression translates to mean both ``mind'' and
``land,'' and thus the two words cannot be separated (Chairman Ronnie
Lupe, pers. comm., 2008). The Apache bald eagle place names evoke an
entire area or ecosystem of which the bald eagle is an intrinsic part.
The place names include entire mountainsides composed of chaparral,
pinyon-juniper woodland, and ponderosa pine forests, always in
proximity to water (i.e., riparian areas) (Lupe et al. pers. comm.
2008).
Bald eagles, including those in the Sonoran Desert Area, typically
nest within 1 mi (1.6 km) of water. Bald eagles require cliff ledges,
rock pinnacles, or large trees or snags in which to construct nests
(Driscoll et al. 2006, pp. 19-20). Those areas most immediately
surrounding the Sonoran Desert Area fall within the Great Basin and
Mohave Deserts, which contain no known breeding eagles or suitable
habitat. These areas lack the appropriate bald eagle habitat parameters
of water, fish, and nesting areas. Nonbreeding bald eagles from other
populations would have to migrate through these areas to reach the
Sonoran Desert Area. Therefore, we believe these desert areas result in
a discontinuity of distribution of breeding birds, rather than as a
barrier to dispersal, and serve to further isolate Sonoran Desert Area
bald eagles from those in other populations.
Bald eagles nesting at high elevation in Arizona in areas in
proximity to the Sonoran Desert Area occupy Petran Montane Conifer
Forest and Plains, and Great Basin Grassland above the Mogollon Rim
(Brown and Lowe 1994, map). These eagles are not believed to have
originated from within the Sonoran Desert Area, as described above.
Similarly, bald eagles occupying these areas are not known to have
occupied Sonoran Desert habitat within the Sonoran Desert Area. These
high-elevation areas appear to be unsuitable to Sonoran Desert Area
bald eagles, as indicated by the lack of emigration to these areas by
eagles originating in the Sonoran Desert Area.
Conclusion on Discreteness
Based on the available information in the petition, scientific
literature, traditional ecological knowledge, and information in our
files at the time of the February 25, 2010, finding, we have determined
that the Sonoran Desert Area population of bald eagles is markedly
separate from other populations of the species due to a lack of
immigration to, and emigration from, surrounding bald eagle
populations, and the fact that the areas immediately surrounding the
Sonoran Desert Area lack the appropriate bald eagle habitat parameters
of water, fish, and nesting areas and contain no known breeding bald
eagles. Therefore, we have determined that the Sonoran Desert Area
population meets the requirements of our DPS Policy for discreteness.
Banding studies and resighting efforts demonstrate that breeding bald
eagles in the Sonoran Desert Area are largely geographically separate
from those in surrounding areas. Limited source populations and
unsuitable habitat in surrounding areas further separate bald eagles in
the Sonoran Desert Area from those in other areas. Although not
absolute, we believe this separation to be marked, and to meet the
intent of the DPS Policy for discreteness.
Significance
Since we have determined that the bald eagles in the Sonoran Desert
Area meet the discreteness element of the DPS Policy, we now consider
the population's biological and ecological significance based on ``the
available scientific evidence of the discrete population segment's
importance to the taxon to which it belongs'' (DPS Policy, 61 FR at
4725). We make this evaluation in light of congressional guidance that
the Service's authority to list DPSs be used ``sparingly'' while
encouraging the conservation of genetic diversity (DPS Policy, 61 FR at
4722; S. Rep. No. 96-151 (1979)). The DPS Policy describes four classes
of information, or considerations, to take into account in evaluating a
population segment's biological and ecological importance to the taxon
to which it belongs. As precise circumstances are likely to vary
considerably from case to case, the DPS Policy does not state that
these are the only classes of information that might factor into a
determination of the biological and ecological importance of a discrete
population.
As specified in the DPS Policy (DPS Policy, 61 FR at 4722),
consideration of the population segment's significance may include, but
is not limited to, the following classes of information:
(1) Persistence of the population segment in an ecological setting
that is unusual or unique for the taxon;
(2) evidence that loss of the population segment would result in a
significant gap in the range of the taxon;
(3) evidence that the population segment represents the only
surviving natural occurrence of a taxon that may be more abundant
elsewhere as an introduced population outside of its historic range;
and
(4) evidence that the discrete population segment differs markedly
from other populations of the species in its genetic characteristics.
Significance of the discrete population segment is not necessarily
determined by existence of one of these classes of information standing
alone. Rather, information analyzed under these considerations is
evaluated relative to the biological or ecological importance of the
discrete population to the taxon as a whole. Accordingly, all relevant
and available biological and ecological information is analyzed for
importance to the taxon as a whole.
[[Page 25806]]
Persistence of the Population Segment in an Unusual or Unique
Ecological Setting
Under the DPS Policy the first consideration in determining whether
a population is significant to the taxon to which it belongs is
``persistence of the population segment in an ecological setting
unusual or unique for the taxon.'' Bald eagles are highly adaptable,
wide-ranging habitat generalists. Across the range of the species,
there is no ``usual'' ecological setting, in terms of the elevation,
temperature, prey species, nest tree species, or type of water source,
for the taxon. The bald eagle is capable of inhabiting areas throughout
North America, so long as a sufficient food source persists. This
contrasts with a situation where a portion of the range of a particular
species exhibits one set of similar habitat characteristics but the
distinct population segment utilizes a different set of habitat
characteristics. For bald eagles, there are many options for suitable
habitat. Though the Sonoran Desert Area may represent a unique set of
habitat characteristics, we cannot say it is unusual or unique for the
bald eagle such that persistence there is significant to the bald eagle
as a whole.
In order to address the court's September 30, 2011, order, we
reviewed previous DPS determinations that described the Service's
analysis of whether the population's persistence in an unusual or
unique ecological setting was significant to the taxon as a whole. A
number of DPS determinations provided little detail--either regarding
which of the four considerations identified in the DPS Policy had
formed the basis for the determination, or regarding how the Service
had analyzed the ``unusual or unique ecological setting''
consideration; this tended to be the case with determinations that were
completed in the ensuing years after the DPS Policy was adopted.
Subsequently, as the determinations provided more detail about the
significance analysis, the analyses of ``unusual or unique ecological
setting'' began to include discussions not only of whether there were
any unusual habitat characteristics, but also of whether persistence
among those habitat characteristics was unusual or unique for the taxon
and made that population significant to the taxon as a whole. Elements
that the Service often considered in these analyses included: (1) The
extent to which there was evidence of adaptations--whether direct
evidence of physical changes or indirect evidence of changes in life-
history traits--that could be significant to the conservation of the
taxon as a whole; and (2) the extent to which the taxon was a habitat
generalist that could adapt to diverse ecological settings. In addition
to those elements, we also considered the extent to which other
populations of the species could or could not persist in the particular
ecological setting such that the persistence of this population in that
setting is biologically or ecologically important to the taxon as a
whole. Consideration of these elements has been incorporated in the way
the Service has interpreted ``persistence in an ecological setting
unusual or unique for the taxon'' under the DPS Policy in previous DPS
determinations.
General information about the biology and life history of the bald
eagle can be found in the Species Information section above. The bald
eagle is able to occupy a broad range of vegetation communities and
ecosystems throughout North America. The bald eagle is distributed
across the North American continent (stretching from the Aleutian
Islands to Baja California, Mexico, and from northeastern Canada to
Florida). The bald eagle breeds at elevations ranging from sea level to
mountains as high as 10,000 feet. It also occupies a range of aridity;
the bald eagle is known to live in some of the driest areas in the
United States and in some of the wettest.
Bald eagles occur throughout North America wherever there is a
sufficient source of prey. Habitat structure and proximity to a
sufficient food source are usually the primary factors that determine
suitability of an area for nesting (Grier and Guinn, p. 44). Nesting
generally occurs along rivers, lakes, and seacoasts in proximity to a
sufficient source of prey. Bald eagles primarily eat fish, but they
will also eat amphibians, reptiles, other birds, small mammals, and
carrion (dead animals) including carcasses of large mammals (e.g.,
cows, elk, deer). Bald eagles typically nest in trees, but have also
been documented nesting on cliffs, on the ground, in mangroves, in
caves, and in manmade structures (e.g., cell phone towers). Bald eagles
are not limited to nesting in or near any particular species of tree,
nor are they limited to eating any particular species or even class of
prey.
The bald eagle has also been shown to be highly adaptable to
changes in the landscape. Data suggest that eagles across many parts of
their range are demonstrating a growing tolerance of human activities
in proximity to nesting and foraging habitats. Eagles in these
situations continue to successfully reproduce in settings previously
considered unsuitable. For example, in Florida, some bald eagle pairs
have shown adaptation to human presence by nesting in residential
subdivisions and commercial and industrial parks, and on cell phone
towers and electric distribution poles. A common thread throughout
these urban and suburban landscapes is the availability of ample food
sources such as natural lakes, rivers, and ponds; artificial stormwater
retention ponds; and public landfills (Millsap et al. 2002, p. 10). In
light of this success in diverse habitats, the bald eagle appears to be
highly adaptable to a variety of habitat conditions based on food
availability.
According to Hunt et al. (1992, p. A163) and Glinski (1998, p. 52),
bald eagle nesting habitats in Arizona are among the most unusual
nesting habitats occupied by the species, with many of the nests
located in open desert under conditions of high heat and low humidity.
On its face, this suggests that the Sonoran Desert Area is an
ecological setting that is unusual or unique for the species. However,
as discussed above, we must assess persistence in this unique or
unusual ecological setting in terms of the biological or ecological
importance of the population's persistence to the species as a whole.
Consistent with previous DPS determinations, we took into account
the ``unusual or unique ecological setting'' consideration by first
evaluating whether there was any evidence of adaptations--whether
direct evidence of physical changes or indirect evidence of changes in
life-history traits--that could be significant to the conservation of
the taxon as a whole. The DPS Policy does not require evidence of
adaptation to a unique or unusual ecological setting in order to make a
finding of significance; however, direct evidence of adaptation to an
ecological setting could be a strong indication that persistence of the
population segment in that ecological setting is significant to the
taxon as a whole. The ecological setting of the Sonoran Desert is
characterized by hot and dry summers. We examined a number of
characteristics of bald eagles in the Sonoran Desert Area to determine
if there was any direct or indirect evidence of adaptations to that
ecological setting such that persistence of that population is
significant (i.e., biologically or ecologically important) to the bald
eagle as a whole. For example, we evaluated whether it is significant
to the bald eagle as a whole that individuals in the Sonoran Desert
Area population are possibly smaller than those in other populations or
that the egg shell porosity for the Sonoran Desert Area population
differs from egg
[[Page 25807]]
shell porosity for other populations. In addition, we evaluated whether
there may have been changes in timing of breeding, specialized feeding
on desert fish, cliff nesting, or juvenile migration characteristics
that make persistence of the population in the Sonoran Desert Area
significant to the taxon.
Bald eagles in the Sonoran Desert Area are smaller in size than
many other bald eagles. One theory presented for this difference is
that the smaller size indicates an adaptation to the hotter, drier
Sonoran Desert environment. In fact, Hunt et al. (1992, p. A165)
suggest that the smaller size of Arizona bald eagles was significant
enough that the introduction of foreign genes into the population might
disrupt coadapted gene complexes (a group of genetic traits that have
high fitness when they occur together, but which without each other
have low fitness) specific to the population.
However, we have found general differences in the size of bald
eagles in the northern latitudes and birds in the southern latitudes.
For instance, Stalmaster (1987, pp. 16-17) notes that northern eagles
are much larger and heavier than their southern counterparts. This is
consistent with Bergmann's Rule, which holds that animal size increases
with increasing latitude due to changes in climate. Consistent with
this rule, Hunt et al. (1992, pp. A158-A161) report that bald eagles in
Arizona are smaller than those in Alaska and the Greater Yellowstone
Region. Supporting this conclusion, Gerrard and Bortolotti (1988, p.
14) note that bald eagles in Florida, which is farther south than
Arizona, are the smallest, with a gradation of large to small from
north to south within the Florida populations. This information
suggests that small size is not an adaptation unique to the Sonoran
Desert but is rather part of the natural variability of the taxon as a
whole.
Another theory presented of possible adaptation from the taxon as a
whole is the possible differences in egg shell porosity of Arizona bald
eagles from bald eagles in other parts of the range of the species.
Hunt et al. (1992) discuss pores in eggshells of bald eagles in
Arizona. Hunt et al. (1992) note that the pores of the eggs assessed
are one to two orders of magnitude smaller than those in California
bald eagle eggs. Some of the public comments received during the public
comment period for our prior status review questioned whether or not
these pores may have an effect on water loss from bald eagle eggs in
the arid environment.
However, Hunt et al. (1992) did not reach any conclusions as to the
significance this difference in egg shell porosity may have to Arizona
eagles. No other reported studies analyzed the potential significance
of this finding. Furthermore, the Hunt et al. (1992) study consisted of
an extremely small sample size of only four eggs. Given the small
sample size of this study, and the lack of analysis in the study, it
would not be scientifically robust to draw any conclusions from the
Hunt et al. (1992) study. As a result, we do not consider the potential
difference of egg shell porosity to be evidence of adaption to the
Sonoran Desert.
Therefore, based on our review of information as it relates to body
size and eggshell porosity, it does not appear that there is direct
evidence of an adaptation of the bald eagle to the Sonoran Desert Area.
Additionally, we did not find any evidence of other traits or factors
that would indicate evidence of an adaptation to the Sonoran Desert
Area.
Next we discuss differences in life-history traits that may be an
indirect indication of an adaptation to the Sonoran Desert Area that
could indicate the population's persistence there is significant to the
taxon as a whole. The life-history traits may include timing of
breeding, feeding habits, nest site selection, and juvenile migration.
We assessed whether bald eagles in the Sonoran Desert Area breed
earlier than many other bald eagles, a change in life history trait
that could indicate there has been an adaptation to the Sonoran Desert
Area setting such that persistence there is significant to the taxon as
a whole. As discussed in the Species Information section above, bald
eagle pairs begin courtship about a month before egg-laying. In the
south, courtship occurs as early as September, and in the north, as
late as May. The nesting season lasts about 6 months.
However, as with bald eagle size variation, a general examination
by latitude reveals differences between bald eagles in northern and
southern regions. Timing of various breeding events in bald eagles is
tied to the latitude of the nesting area, with eagles at more northern
latitudes breeding at later dates (Stalmaster 1987, p. 63). Gerrard and
Bortolotti (1988, p. 76) note that bald eagles in Florida lay eggs from
early November to mid-December. Henry et al. (1993, p. 208) report that
Baja California bald eagles are already incubating by mid January,
which indicates a mid-December to early-January egg-laying period. In
Louisiana, bald eagles lay eggs between October and mid-March, but most
clutches are complete by late December (Service 1989).
The timing of breeding chronology for the bald eagles in the
Sonoran Desert Area is consistent with this latitudinal variation.
Specifically, the breeding chronology of Florida birds (further south
than the Sonoran Desert Area eagles) is even earlier than those in the
Sonoran Desert Area. Therefore, we find it unlikely that the breeding
chronology of bald eagles in the Sonoran Desert Area is a life-history
trait that is biologically or ecologically important to the species as
a whole.
We assessed whether there was evidence that bald eagles in the
Sonoran Desert Area specialized on desert fishes. The most common
fishes eaten by bald eagles in Arizona are: Sonora (Catostomus clarki)
and desert suckers (Catostomus insignis); channel (Ictalurus punctatus)
and flathead catfish (Pylodictis olivaris); common carp (Cyprinus
carpio); largemouth (Micropterus salmoides), smallmouth (Micropterus
dolomieui), yellow (Morone mississippiensis), and white bass (Morone
chrysops); and black crappie (Pomoxis nigromaculatus) (Service 1982, p.
11; Driscoll et al. 2006, p. 6). However, although bald eagles are
opportunistic feeders whose diet is mostly made up of fish, they will
eat birds, amphibians, reptiles, small mammals, and carrion.
Specifically, a study found that the diet of eagles in Arizona based on
prey remains contained 76 percent fish, 14 percent mammals, and 10
percent birds (Hunt et al. 2002, p. 249). The same study found that of
10 breeding areas where prey remains were analyzed, suckers were the
most common prey in only three breeding areas (Hunt et al. 2002, p.
250). Suckers often spawn in riffles, the shallowest of the riverine
habitats, and may be consistently exposed to attack at this stage of
their life cycle (Minckley 1973, pp. 162, 169; Hunt et al. 1992, p.
A57). Water temperature is the catalyst for fish spawning and,
therefore, also causes differences in timing of fish availability
within breeding areas. When suckers (who spawn early) and carp or
catfish (who spawn later) are common, the result may be a prolonged
availability of food for eagles (Hunt et al. 1992, p. A70). Suckers are
the first of essential species to become most available to eagles while
they are incubating eggs or feeding small young. The movement of carp
into shallow water to forage generally occurs seasonally after suckers
have finished spawning (Hunt et al. 1992, p. A70). Because an eagle's
foraging time is reduced due to the necessity of incubation or the care
of newly hatched nestlings unable to regulate their own
[[Page 25808]]
body temperature, the sucker's place in the sequencing of available
prey may be of added importance for successful reproduction for eagles
relying on free-flowing and regulated streams. Additionally, there are
no other fish species used by bald eagles within the Sonoran Desert
Area along rivers that have the same spawning schedule and
accessibility to nesting eagles. Although native Sonoran and desert
suckers seem to be important to bald eagles in the Sonoran Desert Area,
not only for how they become available, but also for when they become
available, there are no data to suggest that bald eagles specialize on
suckers or that foraging on suckers is the result of a unique
adaptation to the desert environment that is biologically or
ecologically important to the species as a whole.
We considered whether cliff nesting is an adaptation to the
conditions in the Sonoran Desert Area that indicates that this
population's persistence there is biologically or ecologically
important to the taxon as a whole. Hunt et al. (1992, p. A-ii) report
that, in the Sonoran Desert Area, when both tree and cliff nests were
available, eagles nonrandomly chose cliffs rather than trees,
indicating that Sonoran Desert Area bald eagles may have a preference
for cliff nests.
Stalmaster (1987, p. 121) noted that cliff nesting is common in
Arizona, but he also noted that exceptions to tree nests occur in other
areas. Gerrard and Bortolotti (1988, p. 41) note that bald eagles in
other areas may nest on cliffs if suitable trees are not available.
This is supported by Buehler (2000), who states that bald eagles use
ground nests (a category in which he includes nests built on cliff
sides) in treeless regions such as Alaska, north Canada, islands off
the coast of California, and Arizona. Bald eagles are also known to
nest on cliffs on the Channel Islands off California (NOAA 2006). Bald
eagles in areas of Alaska where there are no suitable nest trees also
are known to nest on cliffs, sea stacks, hillsides, and rock
promontories (Sherrod et al. 1976, p. 153). It is likely that up to 10
percent of the bald eagles in Alaska nest on the ground (Schempf pers.
comm. 2007). Additionally, ground nesting has also been documented in
limited situations in northwestern Minnesota and Florida (Hines and
Lipke 1991, pp. 155-157; Shea et al. 1979, pp. 3-5). Eagles can also
nest in a variety of unconventional situations, such as utility poles,
abandoned heavy equipment, mangroves, cacti (in Baja), and root wads
washed up on sandbars.
Additionally, bald eagles, across their range, will use whatever
high nest sites are available near the aquatic areas they inhabit. In
the Sonoran Desert Area these sites often happen to be cliffs, but
eagles in the Sonoran Desert Area have also nested in cottonwood,
willow, sycamore, pinyon pine, and ponderosa pine trees. Many Sonoran
Desert Area eagle pairs have built and used both tree and cliff nests
within their territories. This behavior demonstrates the flexibility in
nest site selection that bald eagles have throughout the entire
geographic range of the eagle, suggesting that nest site selection in
the Sonoran Desert area is not likely ecologically or biologically
important to the taxon as a whole.
We also considered whether the juvenile migration characteristics
of Arizona bald eagles may suggest adaptation to the Sonoran Desert
Area that is biologically or ecologically important to the taxon as a
whole. Juvenile bald eagles from Arizona migrate north in the spring
and return to natal territories in the fall (Hunt et al. 1992, p. A-v).
Hunt et al. (2009, p. 125) indicates that juvenile bald eagles from
Arizona exhibit similar migrating characteristics to each other, and
that the similarity of these characteristics, which were exhibited
while migrating solitarily, is evidence of genetic control of
migration. In other words, juvenile bald eagles behave similarly even
while migrating individually. Kerlinger (1989, p. 57) discusses that
natural selection has likely shaped the migratory strategy of birds.
Natural selection likely exerts pressure over time to emphasize the
survival of successful migration strategies and, therefore, successful
genes. In other words, birds that make errors in migration are
eliminated from the population, and do not go on to reproduce and pass
their genes to the next generation. Thus, the birds that do survive
migration and reproduce successfully may become more genetically
similar. Accordingly, there is a belief that the migration
characteristics of bald eagles in the Sonoran Desert Area demonstrates
adaptation in this population with respect to juvenile migratory
behaviors.
Bald eagles as a species exhibit a ``complex pattern of migration
dependent on age of the individual (immature or adult), location of
breeding site (north vs. south, interior vs. coastal), severity of
climate at breeding site (especially during winter but also possibly
during summer), and year-round food availability'' (Buehler 2000). For
example, bald eagles in northeastern North America migrate south in the
fall and return north in the spring, whereas bald eagles in Florida
move north in late spring and early summer and return south in the fall
(Kerlinger 1989, p. 12). This wide variety of migration strategies
employed throughout the range of the species further demonstrates the
flexibility of the species and further suggests that migrating
characteristics of bald eagles in the Sonoran Desert area are not
likely ecologically or biologically important to the taxon as a whole.
Finally, we consider whether there may be other considerations that
make persistence in the Sonoran Desert significant to the bald eagle as
a whole. We conclude that, if other populations of the bald eagle could
not persist in the Sonoran Desert ecological setting, that might be an
indication that the population has adapted in a way that could be
significant to the bald eagle as a whole. We currently have no direct
evidence proving or disproving the ability of other bald eagles to
persist in the Sonoran Desert area. As mentioned above, the best
available information suggests that in fact there has been very little
immigration into the Sonoran Desert area. Nevertheless, an adult bald
eagle located at a Sonora, Mexico breeding area in 1992 possibly
originated from Texas or Florida. This could indicate that, in the rare
instances in which eagle immigrate to the Sonoran Desert Area from
other areas, they are able to persist there. Moreover, based on the
general adaptability shown by eagles throughout their range, there is
no reason to suspect that eagles from outside the Sonoran Desert Area
would not be successful in the Sonoran Desert Area over time.
In summary, the combination of a highly adaptable species
persisting in a varied habitat base leads us to conclude that the
particular variations displayed in the Sonoran Desert Area population
do not make that population more ecologically or biologically important
than any other individual population. Therefore, while the Sonoran
Desert Area represents a unique set of habitat characteristics,
persistence of that population of bald eagles among those habitat
characteristics is not significant (i.e., biologically or ecologically
important) to the taxon as a whole. This is consistent with the
Service's prior interpretations of the DPS Policy, and, as such, the
Service has not adopted a new interpretation of the DPS Policy.
Significant Gap in the Range of the Taxon
The second consideration under the DPS Policy in determining
whether a population is significant to the taxon to which it belongs is
``evidence that loss of the discrete population segment
[[Page 25809]]
would result in a significant gap in the range of a taxon'' (61 FR
4725). We therefore evaluated whether a hypothetical extirpation of the
Sonoran Desert Area bald eagle would leave a significant gap in the
range because of: (1) The size of the Sonoran Desert Area population in
relation to the size of the taxon as a whole; (2) an unlikelihood that
other populations would immigrate and repopulate that part of the
range; (3) distinctive traits or genetic variation among the Sonoran
Desert Area bald eagle; (4) the size of the range of the Sonoran Desert
Area population in relation to the size of the range of the taxon as a
whole; or (5) the role that the geographical location where the Sonoran
Desert Area population occurs plays with respect to the status of the
bald eagle as a whole.
Bald eagles in the Sonoran Desert Area are neither numerous nor
constitute a significant percentage of the total number of bald eagles
throughout the range of the taxon. In 2009, 48 pairs were documented in
the Arizona portion of the Sonoran Desert Area (ADFG 2009a, p. 8),
which is where most of the birds in the Sonoran Desert Area population
occur. This represents less than one half of 1 percent of the current
estimated number of breeding pairs of bald eagles in the lower 48
States. Because the taxon as a whole also includes bald eagles in
Canada and Alaska, the number of breeding pairs in the Sonoran Desert
Area represents much less than one half of a percent of the number of
breeding pairs throughout the range of the species. In addition, the
Arizona portion of the Sonoran Desert Area did not support a large
proportion of the bald eagle population historically. A small number,
estimated at 15-20 breeding pairs, historically bred in this area (Tilt
1976, p. 15). Given the historical and current population number of
bald eagles throughout the range of the taxon, the Sonoran Desert Area
population of bald eagles represents a relatively small number of
breeding pairs in comparison.
Loss of the Sonoran Desert Area bald eagles would be likely to
create some gap in the range of the taxon. As discussed in the
Discreteness section above, available evidence indicates that little
immigration into this population has occurred. The small number of bald
eagles and large distances between neighboring populations currently
limit immigration and emigration between them, and bald eagles in the
neighboring populations would have to increase their population size
and expand their distribution to occupy the gaps, such that loss of the
Sonoran Desert Area population would be likely to create a gap.
Therefore, it is unknown whether bald eagles would naturally repopulate
the Sonoran Desert Area if extirpated.
However, it is not clear that any gap created in the range would be
significant to the taxon as a whole. As discussed above, bald eagles in
the Sonoran Desert Area are neither numerous nor constitute a
significant percentage of the total number of bald eagles throughout
the range of the taxon. Moreover, as discussed previously, there has
been no evidence of distinctive traits or genetic variations among the
Sonoran Desert Area population that suggests that loss of the
population would have a negative effect on the bald eagle as a whole.
For instance, we found no indication that bald eagles in the Sonoran
Desert Area have a specialized prey base of native desert fishes, nor
did we find any direct evidence for adaptation based on difference egg
shell porosity or body size.
Further, the actual amount of suitable bald eagle habitat in the
Sonoran Desert Area is in general limited and represents a minute
fraction of the total suitable habitat available for bald eagles
throughout their range. The limited size of the current and historical
bald eagle population in the Sonoran Desert Area directly reflects that
fact.
Finally, the Sonoran Desert Area itself does not play any
particular role in the life history of the bald eagle such that loss of
that part of the range would have a significant effect on the status of
the species. For example, the Sonoran Desert Area is not the sole
breeding or rearing location for bald eagles, nor is the Sonoran Desert
Area only one of two parts of the species range such that loss of
eagles in one part would result in a significant gap. As stated above,
bald eagles are highly adaptable and are found across a wide range of
habitats in North America.
Having reviewed the best available scientific information with
respect to the biological or ecological significance of the Sonoran
Desert Area bald eagles, we have determined that loss of eagles in the
Sonoran Desert Area would not represent a significant gap in the range
of the bald eagle as a whole.
In conclusion, while the loss of the Sonoran Desert Area bald eagle
would likely result in some gap in the range of the taxon, we find that
the gap does not constitute a significant gap in the range, such that
information reviewed under this element does not suggest that Sonoran
Desert Area bald eagles are biologically or ecologically significant to
the taxon as a whole.
Natural Occurrence of a Taxon Abundant Elsewhere as an Introduced
Population
The third consideration under the DPS Policy is ``evidence that the
discrete population segment represents the only surviving natural
occurrence of a taxon that may be more abundant elsewhere as an
introduced population outside its historic range'' (61 FR 4725). As
discussed above, naturally occurring bald eagles occur throughout much
of their historical range in North America; thus, the Sonoran Desert
Area population does not represent the only surviving natural
occurrence of the bald eagle throughout the range of the taxon in North
America.
Genetic Characteristics
As stated in the DPS Policy, in assessing the significance of a
discrete population, the Service considers evidence that the discrete
population segment differs markedly from other populations of the
species in its genetic characteristics (61 FR 4725).
Limited studies have been completed assessing the genetic
characteristics of Sonoran Desert Area bald eagles in comparison to
bald eagles throughout the rest of the range. Hunt et al. (1992, pp. E-
96 to E-110) contains two studies that represent the genetic work
completed on the Arizona bald eagle population, which includes the
majority of bald eagles in the Sonoran Desert Area. Vyse (reported in
Hunt et al. 1992, pp. E-96 to E-104) completed a DNA fingerprinting
analysis of eagles from California, Arizona, and Florida, and was
unable to identify population-specific genetic markers; however, the
author notes that the results obtained could easily be explained by
sampling procedures. Zegers et al. (reported in Hunt et al. 1992, pp.
E-105 to E-110) conducted an enzyme electrophoresis analysis, and
concluded that, although ``the bald eagle population in Arizona may
have some genetic uniqueness, it is not significantly different from
any other population. * * *'' The authors go on to question the
reliability of the results because of the low numbers of individuals
sampled from most States and because of the few loci examined. In
summary, Hunt et al. (1992, p. A-163) note that neither study detected
alleles or gene fragments that were not detected in other populations.
In conclusion, neither study resolved any specific genetic markers with
which Arizona bald eagles could be differentiated from other
populations. Therefore, given the assumptions and cautions in using the
data, we have determined that the best available data
[[Page 25810]]
do not support a conclusion that bald eagles in the Sonoran Desert Area
have genetic characteristics that are markedly different from other
bald eagles.
DPS Conclusion
On the basis of the best available information, we conclude that
the Sonoran Desert Area population of the bald eagle is discrete, but
it is not significant (i.e., biologically or ecologically important) to
the taxon as a whole. We have reviewed the best available scientific
information, and the evidence relative to natal site fidelity in
breeding birds, the limited number of eagles in neighboring States, and
the results of 30 years of monitoring data indicating that few, if any,
eagles immigrate to or emigrate from the Sonoran Desert Area bald eagle
population. We conclude that the best available scientific information
with respect to the discreteness requirements of the DPS Policy warrant
considering the Sonoran Desert Area bald eagle population as discrete
from other bald eagle populations in North America.
We considered the four classes of information listed in the DPS
Policy as possible considerations in making a determination as to
significance, as well as all other information that might be relevant
to making this determination for the Sonoran Desert Area population.
The adaptability of the bald eagle allows its distribution to be
widespread throughout the North American continent in a variety of
habitat types. Further, the Sonoran Desert Area bald eagles do not
appear to exhibit any direct or indirect adaptation or behavioral
advantage that would indicate its persistence in the Sonoran Desert
Area is biologically or ecologically important to the taxon as a whole.
Moreover, we considered the other three considerations that the DPS
Policy sets out for evaluating significance, and none of them provides
evidence that the population is significant to the bald eagle as a
whole: Loss of the population would not result in a significant gap in
the range; the population does not represent the only surviving natural
occurrence of the bald eagle; and the population's genetic
characteristics do not differ markedly from those of other bald eagle
populations.
We conclude that the discrete Sonoran Desert Area population of
bald eagle does not meet the significance criterion of the DPS Policy,
as detailed above and, therefore, is not a DPS pursuant to our DPS
Policy. As a result, the Sonoran Desert Area population of bald eagles
is not a listable entity under section 3(16) of the Act.
The DPS Policy sets forth a three-step process for determining
whether a vertebrate population as a separate entity warrants listing:
(1) Determine whether the population is discrete; (2) if the population
is discrete, determine whether the population is significant to the
taxon as a whole; and (3) if the population is both discrete and
significant, then evaluate the conservation status of the population to
determine whether it is endangered or threatened (typically presented
as a 5-factor analysis of the threats to the discrete population
(threats assessment) followed by a determination of whether the
population meets the definition of ``endangered species'' or
``threatened species''). Although we have determined that the Sonoran
Desert Area population of the bald eagle does not qualify as a DPS and,
therefore, is not a listable entity because it is not significant to
the taxon as a whole. However, we provide below a threats assessment of
the Sonoran Desert Area population of the bald eagle and a
determination of its conservation status. The DPS Policy neither
requires nor prohibits completion of a threats assessment once we have
determined that a population does not qualify as a DPS. Nevertheless,
in this instance, we concluded that completing a threats assessment--
and detailing the nature, scope, and likely effect of the threats to
the population and the species--would provide us and the public with
valuable information for understanding the status of the population.
Summary of Information Pertaining to the Five Factors
As discussed above, the bald eagle is known to have bred in every
State and province in the United States and Canada except Hawaii
(Johnsgard 1990, p. 145; Hunt et al. 1992, p. A9). Gerrard and
Bartolotti (1988, p. 2) noted that, at the time Europeans first arrived
on North America, bald eagles were believed to have nested on both
coasts, along all major rivers and large lakes in the interior from
Florida to Baja California in the south, and north to Labrador and
Alaska. In general, three factors seem to determine the distribution
and abundance of bald eagles and other raptors (i.e., birds of prey):
(1) An adequate and accessible supply of food, (2) availability of nest
sites, and (3) suitable foraging habitat (Johnsgard 1990, pp. 15-17).
Specifically, the bald eagle needs areas for nesting, perching,
roosting, and foraging (Stalmaster 1987, pp. 119-131) and a reasonable
degree of freedom from disturbance during the nesting season (Johnsgard
1990, p. 145). Hunt et al. (1992, p. A-v) goes further to suggest that
the features of bald eagle habitat in Arizona that render it suitable
for breeding include: (1) Nesting substrate offering security from
large predators and human disturbance; and (2) two or more of the
following fish taxa occurring in substantial numbers: carp, suckers
(spp.), catfish (spp.), and perciforms (from the order Perciformes).
Factors that appear to increase habitat quality include: (1) Reservoirs
supporting warm water fisheries; (2) reservoir inflow areas; and (3)
areas of river habitat containing fast, shallow water, moderate slope,
turbulence, and exposed substrate that are maintained under a wide
variety of flows.
Observations of bald eagles in Arizona are mentioned in the
literature as early as 1866 by Coues in the vicinity of Fort Whipple
(now Prescott). Henshaw reported bald eagles south of Fort Apache in
1875. The first bald eagle breeding information was recorded in 1890
near Stoneman Lake by S.A. Mearns. Additionally, Bent reported the
presence of breeding eagles on the Salt River Bird Reservation, which
was inundated by Roosevelt Lake in 1911. There are also reports from
the 1930's of bald eagles nesting along rivers in the White Mountains
and along the Salt and Verde Rivers in central Arizona (Hunt et al.
1992, pp. A11-A12).
The bald eagle population of the Southwest Recovery Region, as
identified in the Service's final recovery plan for the species,
reaches all of New Mexico and Arizona, throughout Oklahoma and Texas
west of the 100th meridian, and the area of California bordering the
Lower Colorado River (Service 1982, p. 1). The vast majority of the
breeding bald eagles from this population are found within the State of
Arizona, most of which are located within the Sonoran Desert Area. The
occurrence of breeding bald eagles in the State of New Mexico is very
limited (USFS 2004, p. 153). In 2001, the New Mexico Department of Game
and Fish (NMDGF) reported the occurrence of four bald eagle nest sites,
all on private lands, in New Mexico.
Nationwide, bald eagles are known to nest primarily along seacoasts
and lakeshores, as well as along banks of rivers and streams
(Stalmaster 1987, p. 120). In Arizona, bald eagle breeding areas (eagle
nesting sites and the area where eagles forage) are located in close
proximity to a variety of aquatic sites, including reservoirs,
regulated river systems, and free-flowing rivers and creeks. In
Arizona, nests are placed mostly on cottonwood trees, cliff edges, and
rock pinnacles and may be used year after year. However, living and
[[Page 25811]]
dead junipers, pinyon pines, sycamores, willows, and ponderosa pines,
and artificial structures also have supported eagle nests (Driscoll et
al. 2006, p. 4). In 1992, of 111 known nests in Arizona within 28
breeding areas, 48 percent were on cliffs or pinnacles, 51 percent were
on trees or snags, and one percent was on artificial structures. For
breeding areas where both cliff and tree nests were available, cliff
nests were selected 73 percent of the time, while tree nests were
selected 27 percent of the time (Hunt et al. 1992, p. A17).
Additionally, eagles nesting on cliffs were found to be slightly more
successful in raising young to fledgling, though the difference was not
statistically significant (Hunt et al. 1992, p. A17).
In the Sonoran Desert Area, essential bald eagle activities such as
nesting, perching, roosting, and foraging occur from and in the large
woody tree component of the riparian habitat found along rivers and
streams. Eagles nesting in trees within the Sonoran Desert Area are
less susceptible to heat stress and parasites than those nesting in
cliff or pinnacle nests, but are more vulnerable to disturbance from
the ground and from inundation during flooding (Hunt et al.1992, p.
A17). Eaglets (young eagles) in tree nests are less likely to die from
premature fledging. An abundance of trees provides more perching
locations to capture prey, more locations to place nests, and greater
opportunities to partition resources in order to increase territory
density (Hunt et al.1992, pp. Aii, A21, A135).
The importance of riparian trees is demonstrated along the lower
Verde River in Arizona, where the densest population of nesting bald
eagles (seven territories along 30 river kilometers (18.6 miles))
exclusively uses cottonwood trees for nest placement. In Arizona, the
majority of nests are located in the Upper and Lower Sonoran Life Zones
(zones of plant and animal life associated with a given elevation),
including the riparian habitats and transition areas of both zones
(Hunt et al. 1992, p. A17). Representative vegetation of these life
zones includes Arizona sycamore (Platanus wrightii), blue palo verde
(Parkinsonia florida), cholla (Opuntia and Cylindropuntia spp.),
Fremont cottonwood (Populus fremontii), Gooding willow (Salix
gooddingii), mesquite (Prosopis spp.), saguaro (Carnegiea gigantea),
and tamarisk or salt cedar (Tamarix pentandra; an exotic species)
(Brown 1994, p. 200).
Bald eagles primarily eat fish, but they will also eat amphibians,
reptiles, birds, small mammals, carrion (dead animals), and carcasses
of large mammals (cows, elk, deer, etc.). Their food habits can change
daily or seasonally, but when a choice is available, bald eagles
invariably select fish over other prey. Bald eagles will scavenge,
steal, or actively hunt to acquire food. Carrion constitutes a higher
proportion of the diet for juveniles and subadults than it does for
adult eagles. Bald eagles are primarily sit-and-wait hunters, perching
in trees in order to detect available prey (Stalmaster 1987, p. 104).
Food strongly influences bald eagle productivity (young fledged per
occupied territory) (Newton 1979, pp. 95-96, 101-106; Hansen 1987, p.
1389). A female's health in the months preceding egg-laying can affect
egg production, and prey availability during the breeding cycle affects
the survivorship of nestlings and post-fledging juveniles. Any factor
affecting the adults' ability to acquire food can influence
productivity and adult survival (Newton 1979, pp. 95-96, 101-106).
The most common fishes eaten in Arizona are Sonora (Catostomus
clarki) and desert suckers (Catostomus insignis); channel (Ictalurus
punctatus) and flathead catfish (Pylodictis olivaris); common carp
(Cyprinus carpio); largemouth (Micropterus salmoides), smallmouth
(Micropterus dolomieui), yellow (Morone mississippiensis), and white
bass (Morone chrysops); and black crappie (Pomoxis nigromaculatus).
Less common are roundtail chub (Gila robusta), green sunfish (Lepomis
cyanellus), bluegill (Lepomis macrochirus), tilapia, and rainbow trout
(Oncorhynchus mykiss) (Service 1982, p. 11; Driscoll et al. 2006, p.
6). The introduction of predatory flathead catfish in the late 1970s
nearly extirpated native fish populations on the upper Salt River
(Driscoll et al. 2006, p. 19). Flathead catfish, while available as
bald eagle prey when smaller, grow to large sizes (up to 50 pounds, or
22.6 kilograms) making them unavailable as a prey item (i.e., too large
for bald eagles to take). Flathead catfish populations have increased
while other fish species have decreased (Driscoll et al. 2006, p. 19).
The Arizona Game and Fish Department (AGFD) notes that apparent
changes in eagle productivity observed from before 1985 and after 1985
could be the result of a difference in monitoring protocols. Starting
in 1985, their protocol incorporated monthly helicopter surveys of all
breeding areas. The AGFD noted that the average productivity rate of
0.78 observed in Arizona between 1987 and 2005 is consistent with that
observed in other areas of the species' range with larger populations,
including Minnesota, British Columbia, Interior Alaska, and Washington
(Driscoll et al. 2006, p. 5). Due to rugged terrain, the earliest
formal surveys in Arizona--in the 1970's--only detected bald eagle
breeding areas that were easily accessible (e.g., along rivers and
streams) (Driscoll et al. 2006, p. 9). Following intensive survey
efforts over the last 25 years, the AGFD is aware of more breeding
areas, and habitat conditions within them varies greatly. As a result,
the AGFD is currently tracking productivity in breeding areas with a
variety of habitat conditions, rather than tracking productivity in
only those breeding areas that were easily detected. While the number
of breeding areas detected in subsequent surveys in Arizona has
increased, there is no expectation that pairs using these breeding
areas would demonstrate increased reproductive performance.
Productivity data between 1987 and 2008 indicates less variability. For
example, in 1971, with only three known breeding areas, productivity
was 1.33; in 1972 productivity was 0.0; and in 1973 productivity was
1.4. By comparison, with more breeding areas known, productivity now
varies by only 0.20 to 0.30 units (Driscoll et al. 2006, pp. 48-50;
AGFD 2007, pp. 33-34; AGFDa 2008, pp. 38-39).
The Sonoran Desert Area population consists of those bald eagles
that breed predominantly within central and southern Arizona; Sonora,
Mexico (Sonora); and portions of southeastern California along the
Colorado River as described in detail above (see Distinct Population
Segment). Based on opportunistic monitoring of the single nest located
in southern California at the Copper Basin breeding area conducted
since 2001 (Melanson 2006a, 2007, 2008, pers. comm.), we have limited
information on potential threats to this breeding area, and demographic
data from this site was not collected using the same protocol
established in Arizona. We include information from this breeding area
in the following threats analysis where appropriate. Information on
breeding success in Sonora is limited. Bald eagle territories were
first recorded in Sonora along the Rio Yaqui drainage in 1986 (Brown et
al. 1986, pp. 7-14). Since that time, a total of eight bald eagle
breeding areas have been verified (Driscoll and Mesta 2005, in prep.).
Surveys there irregularly occur due to difficulties in accessing
breeding areas. However, given the limited number of breeding areas and
the infrequency of breeding noted during survey years, the overall
impact of productivity from Sonora bald eagles
[[Page 25812]]
to the total productivity of the Sonoran Desert Area population of the
bald eagle is minimal.
Historical records, literature, past reports, and interviews with
agency personnel and other people knowledgeable about bald eagles in
Arizona indicated that there was one known breeding area by the 1920s,
two by the 1930s, four by the 1940s, five by the 1950s, six by the
1960s, and eight by the 1970s (Hunt et al. 1992, pp. C56-C61). The
number of known breeding areas within the Sonoran Desert Area increased
from a low of three in 1971 to a high of 52 in 2009. In addition, there
were seven breeding areas located within Arizona but outside of the
Sonoran Desert Area in 2009. From 1985 to 2009, productivity within the
Sonoran Desert Area has ranged from a low of 0.54 in 1990 and 1992 to a
high of 1.17 in 2008. The mean annual productivity for this time period
in the Sonoran Desert Area was 0.81 (AGFD 2004, pp. 30-31; AGFD 2005,
pp. 34-35; AGFD 2006a, pp. 35-36; AGFD 2007, pp. 33-34; AGFD 2008a, pp.
38-39; Allison et al. 2008, pp. 17-18; AGFD 2009a, pp. 42-43). For
comparison, productivity in North America averaged 0.34 in three
declining bald eagle populations, as compared to 0.75 in seven stable
populations and 1.03 in four increasing populations (Swenson et al.
1986, p. 25).
Productivity data alone does not provide a clear indication of the
status of a population without considering the additional influence of
other demographic variables (e.g., survival, number of breeding areas).
When all of this data is considered together, as is done through a
population viability analysis (see Factor A discussion), estimates of
population growth and extinction probabilities can be generated. For
bald eagles nesting in the Sonoran Desert Area of Arizona, a population
viability analysis conducted by the Service resulted in an estimated
annual population growth rate of two percent, and none of the model
iterations resulted in extinction of the population (Millsap 2009, in
prep.) (see Factor E, Demographic Factors discussion).
Five-Factor Analysis
Pursuant to section 4 of the Endangered Species Act of 1973, as
amended, we must determine whether any species, subspecies, or DPS of
vertebrate taxa is an endangered or threatened species because of any
of the following five factors: (A) Present or threatened destruction,
modification, or curtailment of habitat or range; (B) overutilization
for commercial, recreational, scientific, or educational purposes; (C)
disease or predation; (D) inadequacy of existing regulatory mechanisms;
or (E) other natural or manmade factors affecting its continued
existence. The Endangered Species Act identifies the five factors to be
considered, either singly or in combination, to determine whether a
species may be threatened or endangered. Our evaluation of these
threats in terms of the petitioned action to list the Sonoran Desert
Area population of the bald eagle as a distinct population segment
(DPS) is presented below. Throughout this finding we refer to the
Sonoran Desert Area population of the bald eagle, because that is the
petitioned entity; however, we have determined that this population
does not constitute a DPS and, therefore, is not a listable entity.
Even though we have made this determination, we conducted the five-
factor analysis below as an exercise to review the status of the
Sonoran Desert Area population of the bald eagle.
In considering what factors might constitute a threat, we must look
beyond the mere exposure of the species to the factor to determine
whether the species responds to the factor in a way that causes actual
impacts to the species. If there is exposure to a factor, but no
response, or only a positive response, that factor is not a threat. If
there is exposure and the species responds negatively, the factor may
be a threat and we then attempt to determine how significant a threat
it is. If the threat is significant, it may drive or contribute to the
risk of extinction of the species such that the species warrants
listing as threatened or endangered as those terms are defined by the
Endangered Species Act. This does not necessarily require empirical
proof of a threat. The combination of exposure and some corroborating
evidence of how the species is likely to be negatively affected could
suffice. The mere identification of factors that could affect a species
negatively is not sufficient to compel a finding that listing is
appropriate; we require evidence that these factors are operative
threats that act on the species to the point that the species meets the
definition of ``threatened species'' or ``endangered species'' under
the Endangered Species Act.
The following analysis considers all known threats to bald eagles
in the Sonoran Desert Area, as described below. Factors that are
believed to have affected or continue to affect bald eagles in the
Sonoran Desert Area include the degradation or loss of riparian
habitat; loss of surface flows from groundwater pumping and surface
water diversions; demographic factors; declining prey base;
contaminants, pollutants, and eggshell thinning; climate change; and
human disturbance. It is important to recognize that in most areas
where bald eagles occur, two or more factors may be acting in
combination in their influence on individuals of the population, the
entire local population, or the suitability of habitat.
Within the Sonoran Desert Area, bald eagles on the Verde River
accounted for 44 percent of total productivity between 1971 and 2008
while breeding areas on the Salt River accounted for an additional 34
percent of total productivity. In total, 78 percent of bald eagle
productivity in the Sonoran Desert Area, exclusive of Sonora, is tied
to breeding areas along these two river systems. Therefore, the
following analysis places emphasis on threats to breeding areas along
these two river systems. We also included threats to other river
systems--including the Agua Fria, Bill Williams, and Gila Rivers--in
our analysis of threats to bald eagles in the Sonoran Desert Area.
In our analysis of Factors A through E below, we describe current
threats, as well as threats that we anticipate will increase, or will
be realized in the future. For populations within Arizona, our analysis
benefitted from the availability of specific research, monitoring, and
other studies. The analysis of these factors as they pertain to the
status and threats to the bald eagle in mainland Sonora is broader in
scope, focusing on regional or statewide areas, because there has been
less work completed for the bald eagle in this area. In some instances,
we include a discussion on more refined geographic areas of Mexico when
supported by the literature.
Traditional Ecological Knowledge
We included traditional ecological knowledge from Native American
tribes in our consideration of threats to the Sonoran Desert Area
population of bald eagle. Traditional ecological knowledge includes an
intimate and detailed knowledge of plants, animals, and natural
phenomena; the development and use of appropriate technologies for
hunting, fishing, trapping, agriculture, and forestry; and a holistic
knowledge, or ``world view,'' that parallels the scientific discipline
of ecology (Bourque et al. 1993, p. vi). Native people depended upon
the animals and plants of these environments for food, clothing,
shelter, and companionship and as a result developed strong ties to the
fish and land animals, the forests, and the grasslands (Pierotti and
Wildcat 1999, pp. 192-195). We include bald eagle
[[Page 25813]]
traditional ecological knowledge provided to us by the White Mountain
Apache Tribe, San Carlos Apache Tribe, Tonto Apache Tribe, Yavapai-
Apache Nation, Salt River-Pima Maricopa Indian Community, Tohono
O'odham Nations, and Fort McDowell Yavapai Nation.
Traditional ecological knowledge from the White Mountain Apache
Tribe, San Carlos Apache Tribe, Tonto Apache Tribe, and Yavapai-Apache
Nation (collectively referred to as Western Apache) indicates that bald
eagles are absent from many nest sites where they were once observed.
Feathers originating from native, living, wild bald eagles are obtained
year round for ceremonial purposes. Part of the ritual use of these
feathers requires obtaining power from the place in which the eagle
lives, and, thus, these places are considered extremely powerful and
are known to the user. The task of obtaining feathers is only
accomplished by certain individuals who have cultural knowledge and the
traditional ecological knowledge of these places. This knowledge is
gained from years of experience through observation, which is then
orally transferred to the next generation. Western Apache traditional
ecological knowledge suggests that irresponsible urban expansion,
agriculture, mining, and resultant climate change have brought the
earth, and bald eagle habitat, to a crisis point. Traditional
ecological knowledge additionally suggests that the riparian systems on
which bald eagles depend have been severely damaged, and continue to be
threatened with upland watershed decline, the region's dwindling water
resources, multiple sources of pollution, water rights conflicts, and
the spread of nonnative fauna species (Lupe et al. 2008, pers. comm.).
Tribal information is consistent with published information documenting
the modification and destruction of aquatic and riparian communities in
the southwestern United States (Medina 1990, p. 351; Sullivan and
Richardson 1993, pp. 35-42; Fleischner 1994, pp. 630-631; Stromberg et
al. 1996, pp. 113, 123-128; Belsky et al. 1999, pp. 8-12; Webb and
Leake 2005, pp. 305-310).
Traditional ecological knowledge from the Western Apache reports a
decline of the bald eagle population and nesting sites throughout
Arizona over the past 150 years. Bald eagle nests are no longer present
in sites where they were known to the Western Apache, including Warm
Springs Canyon, Black River Canyon, Paymaster Canyon, and Salt Creek
Canyon on the San Carlos Reservation. According to traditional
ecological knowledge of the Western Apache, more bald eagles were
previously observed below Coolidge Dam and at Talkalai Lake than
currently exist. In addition, bald eagles are no longer present in the
canyon above Clarksdale, Box Canyon, Fossil Creek, Courthouse Butte
around the Sedona area; Mazatzal Mountains near Payson; and Hackberry
Mountain southeast of Camp Verde (Sparks 2009, entire). According to
transcripts from a government-to-government consultation meeting held
on July 3, 2008, the Fort McDowell Yavapai Nation reported up to 15
bald eagle nests historically occurred on their reservation lands, and
now there are four. Western Apache experts with traditional ecological
knowledge about the bald eagle note atmospheric changes, and alteration
in bee, wasp, and hornet populations, as a few of the many key factors
in bald eagle habitat decline. Declines and shifts in distribution and
abundance in bald eagles in Arizona may have occurred within the last
150 years from areas where habitat and riverine systems may no longer
exist (Mearns 1890, p. 53; Hunt et al. 1992, Ai, A10-A12; Mighetto et
al. 2009, pp. 6-8). For example, Mighetto et al. (2009) reported eagles
historically occupying areas around Window Rock, Lake Mead, Anderson
Mesa near Big Horse Lake, Stoneman Lake, Fort Apache, and Mt. Graham,
but they no longer exist in these locations.
The Salt River Pima-Maricopa Indian Community believes the Bald and
Golden Eagle Protection Act (see discussion under Factor D below) will
not provide the necessary level of protection needed to keep the bald
eagle in the Sonoran Desert Area viable. The Community further believes
that habitat protection is uncertain based on the new regulatory
definition of ``disturb,'' which is untested in the courts. The Western
Apache have expressed similar concern that habitat will not be
protected. The Western Apache Tribes and Nation have indicated that,
within reservation boundaries, there may be inadequate resources to
address these threats. They indicate that the incentive for poaching
bald eagles is high in Apache communities, primarily due to desperate
economic conditions. A single bald eagle can be sold for more than
$5,000. The Western Apache believe that even a perceived loss of
protection for the bald eagle could bring about an increase in poaching
activities. Tribal law enforcement agencies, already facing funding
shortages, would be unable to respond properly to such threats (Lupe et
al. pers. comm. 2008).
A. Present or Threatened Destruction, Modification, or Curtailment of
the Species' Habitat or Range
Within Arizona, bald eagles are listed as a Tier 1a ``species of
greatest conservation need'' in the State's ``Comprehensive Wildlife
Conservation Strategy'' (AGFD 2006b, p. 155). Additional provisions are
in place for the management of bald eagles. The management of bald
eagles in Arizona is also overseen by the Southwestern Bald Eagle
Management Committee, which is a multiparty committee initiated in 1984
that focuses on coordination of bald eagle conservation efforts in
Arizona across various land ownerships. The AGFD, in 2006, developed
the ``Conservation Assessment and Strategy for the Bald Eagle in
Arizona,'' which described the current threats to bald eagles in
Arizona and identified the best management practices necessary to
maintain their distribution and abundance post-delisting. The
``Conservation Assessment and Strategy for the Bald Eagle in Arizona''
has been implemented following the signing of a Memorandum of
Understanding in 2007. As a result, the AGFD continues to conduct bald
eagle winter counts, monitor bald eagle distribution and productivity,
support the ABENWP, and conduct other activities identified in the
``Conservation Assessment and Strategy for the Bald Eagle in Arizona.''
The AGFD believes that these conservation efforts will sufficiently
manage the threats to bald eagles in the Sonoran Desert Area of Arizona
absent the protections under the Endangered Species Act (AGFD 2008b, p.
6).
A number of potential threats to bald eagle habitat in the Sonoran
Desert Area have been identified by the petitioners, the AGFD, and the
Service. In our review of the best scientific and commercial data
available, activities that are potentially affecting bald eagles and
their habitat in the Sonoran Desert Area include urban and rural
development, livestock grazing, groundwater pumping, and surface water
diversions, in that each of these activities (or a combination of these
activities, acting in concert) could degrade or remove riparian
habitat. Because bald eagles rely on aquatic ecosystems as a source of
fish for survival and reproduction and trees for nesting, any loss or
degradation of riparian habitat is of particular concern (Stalmaster
1987, pp. 159, 170-171). The ``Conservation Assessment and Strategy for
the Bald Eagle in Arizona'' identified riparian degeneration as a
management challenge for 25 of 45 known breeding areas (or 58 percent)
[[Page 25814]]
located within the Sonoran Desert Area of Arizona at that time
(Driscoll et al. 2006, pp. 51-53). Additionally, the potential loss of
surface flows within sections of the Gila, Salt, Verde, Agua Fria, or
Bill Williams Rivers would likely have negative impacts on the density
and distribution of prey and the health and persistence of riparian
vegetation. Below we present information about these factors, and
discuss the magnitude and extent of the impacts from these factors on
the Sonoran Desert Area population of the bald eagle.
Degradation and Loss of Riparian Habitat
Riparian communities are sensitive to even low levels (less than 10
percent) of urban development within a watershed (Wheeler et al. 2005,
p. 154). Development along or in proximity to riparian zones can alter
the nature of stream flow dramatically, changing once-perennial streams
into ephemeral streams, which has direct consequences on the riparian
community (Medina 1990, pp. 358-359). The distribution of breeding bald
eagles in the Sonoran Desert Area follows major watersheds, with the
highest productivity occurring along the Salt and Verde Rivers, and
some of the breeding areas along these rivers are located in close
proximity to metropolitan areas. The conversion of perennial streams
into ephemeral (lasting a short time) streams or loss of open space can
directly affect bald eagles along these rivers (Medina 1990, pp. 358-
359; Ewing et al. 2005, p. 11). Loss of water and conversion to
ephemeral streams eliminates or reduces the quality of riparian
habitat, including the trees on which bald eagles depend for nesting
and perching. Loss of open space or clearing of habitat for development
removes vegetation directly, either in the watershed or in the riparian
areas themselves, making the areas less suitable for bald eagles by
removing key habitat components (e.g., water, large trees).
The influence of urbanization and development can be observed
within the greater Phoenix, Arizona, area, where impacts have modified
riparian vegetation, structurally altered stream channels, facilitated
nonnative fish species introductions, and dewatered large reaches of
formerly perennial rivers where the bald eagle historically occurred
(portions of the Gila and Salt Rivers). Urbanization on smaller scales
can also affect habitat suitability for the bald eagle. Regional
development and subsequent land use changes spurred by increasing human
populations along lower Tonto Creek and within the Verde Valley may
negatively affect the suitability of this habitat for bald eagles by
reducing the quantity and quality of aquatic resources for native fish
and reducing the width of riparian habitat (Paradzick et al. 2006, pp.
89-90). Studies conducted in other portions of the range of the bald
eagle in North America, such as the Chesapeake Bay, indicated that
human development and low availability of suitable perch trees combined
to affect bald eagle use of shoreline habitat (Chandler et al. 1995,
pp. 328-330). Bald eagles there preferred shoreline segments that
contained more suitable perch trees, more forest cover, and fewer
buildings. However, to have a significant effect, urbanization and
development must be occurring at a scale and intensity that results in
a risk to the Sonoran Desert Area population of the bald eagle at the
population level. The ``Conservation Assessment and Strategy for the
Bald Eagle in Arizona'' identified development as a management concern
in 4 of 45 bald eagle breeding areas (or 9 percent) located within the
Sonoran Desert Area of Arizona at that time (Driscoll et al. 2006, pp.
51-53). Although urbanization and development may be affecting breeding
areas at a localized level, it does not appear that they are currently
a threat at the population level, because the population remains stable
or increasing.
The effects of urban and rural development on riparian habitat are
expected to increase as human populations increase. Arizona increased
its population by 394 percent from 1960 to 2000, and is second only to
Nevada as the fastest growing State in terms of human population
(Social Science Data Analysis Network (SSDAN) 2000, p. 1). Over the
same time period, population growth rates increased in Arizona counties
where the bald eagle occurs: Maricopa (463 percent), Yavapai (579
percent), Gila (199 percent), Graham (238 percent), Apache (228
percent), and La Paz (142 percent) (SSDAN 2000). Population growth
trends in Arizona are expected to continue into the future. The Phoenix
metropolitan area, founded in part due to its location at the junction
of the Salt and Gila Rivers, is currently a population center of 3.63
million people. Arizona is predicted to have the sixth largest net
increase in population (slightly over two million people) in the nation
between 1995 and 2025 (U.S. Department of Commerce 1997, p. 1). The
human population in Maricopa County alone is expected to reach five
million people by 2025 (City of Phoenix 2004, p. 18), and the county
stands to lose up to an estimated 347.2 square miles of open space that
are currently in the path of development (Ewing et al. 2005, p. 11).
The human population in two towns along the Verde River, Cottonwood
and Camp Verde, is expected to grow by approximately 70 and 77 percent,
respectively, between 2006 and 2040 (Arizona Department of
Administration 2012). The town of Chino Valley, at the headwaters of
the Verde River, grew by 22 percent between 2000 and 2004; Gila County,
which includes portions of the Salt River and Tonto Creek, grew by 20
percent between 2000 and 2003 (U.S. Census Bureau 2006). Human
population growth is expected to continue to affect the riparian and
aquatic communities of the Verde Valley through increased demand for
water, increased runoff, shortened return intervals on flood events,
water quality impacts, and increased recreational impacts where bald
eagles are concentrated (Girmendock and Young 1997, p. 57; American
Rivers 2006, p. 30; Paradzick et al. 2006, p. 89).
The human population and associated recreational developments in
the Sonoran Desert Area, which are often tied to water bodies and
riparian areas, are expected to continue to grow into the future. In
the Sonoran Desert Area, an expanding human population has led to
higher recreational use of riparian areas, as evidenced along reaches
of the Salt and Verde Rivers in proximity to the Phoenix metropolitan
area. Recreational impacts can include direct habitat losses for
development of recreational facilities and infrastructure or indirect
loss of habitat as a result of human disturbance (see Factor E for
further discussion). Developments within occupied breeding areas
include a turnaround for river tubing near Bulldog Cliffs (Salt River)
and lakeside resorts on the north shore of Lake Pleasant. Additional
developments that may affect bald eagle breeding areas include: a four-
lane boat launch and a 1,000 person per day recreation area on Bartlett
Lake; a new day use and emergency boat launch constructed on the lower
Salt River; a new RV park constructed within 1300 feet (396.2 meters)
of a nest on the lower Verde River; and a 100-unit campground and boat
ramp along Tonto Creek (Driscoll et al. 2006, p. 14).
In many of the breeding areas within the Sonoran Desert Area of
Arizona, effects from development have been mitigated through the
implementation of seasonal closures and monitoring by the Arizona Bald
Eagle Nest Watch Program (ABENWP). The ABENWP, managed by the AGFD,
closely monitors breeding bald eagles in areas with high
[[Page 25815]]
recreational pressure. This program was initiated in 1978 with the
goals of public education, data collection, and conservation of the
species. Nest watchers collect behavioral data, contact and educate the
public in the vicinity of breeding areas, and identify potential
threats to the breeding success of bald eagles. Funding for the ABENWP
comes from a variety of sources, including State Wildlife Grants,
donations, AGFD Heritage Funds (State lottery), matching funds for
Federal grants, and contributions from Federal agencies. As a result of
the bald eagle being delisted, there is the potential that the ABENWP
could face funding shortages or that the bald eagle could receive less
priority from partner agencies; however, there is currently no
indication that either of these scenarios has occurred or will occur in
the future.
The AGFD's Projects Evaluation Program is available for Federal
agencies or companies with a Federal nexus. This program can be used to
evaluate the impacts of planned or future projects in areas where there
may be a species of concern. The AGFD believes the program will help to
ensure bald eagles and their habitat are considered and evaluated for
possible effects from development projects (Driscoll et al. 2006, p.
14). In the future, similar levels of development and modification as
those described above can be expected as recreational facilities age
and recreational pressures increase with increasing human populations.
However, as evidenced by the continued reproductive success (e.g.,
pairs continue to produce young) of the above affected breeding areas,
the ability of the bald eagle in the Sonoran Desert Area to adapt to
increases in the human population and habitat modifications is an
indication that these actions are not posing a significant risk at the
population level.
Livestock grazing has been a prevalent industry in the Southwest
for 200 years or more. Poorly managed livestock grazing has damaged
approximately 80 percent of stream, cienega (spring), and riparian
ecosystems in the western United States (Kauffman and Krueger 1984, pp.
433-435; Weltz and Wood 1986, pp. 367-368; Waters 1995, pp. 22-24;
Pearce et al. 1998, p. 307; Belsky et al. 1999, p. 1). Overgrazing by
domestic livestock has been a significant factor in the modification
and loss of riparian habitats in the arid western United States
(Schultz and Leininger 1990, p. 295; Belsky et al. 1999, pp. 1-3). If
not properly managed, livestock grazing can significantly alter
watershed hydrology; water quality; aquatic and riparian ecology; and
the structure and composition of riparian plant communities. Excessive
grazing can also prevent the establishment of seedlings (Carothers
1977, p. 2; Glinski 1977, pp. 119-121), which limits the growth of
future nest and roost trees for bald eagles (Driscoll et al. 2006, p.
4). Important features of bald eagle habitat--such as large trees for
roosting and nesting, sufficient flows, water temperatures, and water
quality--are most affected by improper livestock grazing in riparian
areas. Currently, active grazing is occurring within the Verde River
floodplain in the Verde Valley, lower Verde River, and upper Salt
River.
The impacts of improper livestock grazing have been reduced on many
streams, in part through consultations completed under section 7 of the
Endangered Species Act and in part through improved grazing management
practices. Some of the consultations were for other species that use
the same streams as habitat or for foraging (e.g., Southwestern willow
flycatcher (Empidonax trailii extimus), razorback sucker (Xyrauchen
texanus), spikedace (Meda fulgida), loach minnow (Tiaroga cobitis)).
Therefore, despite the delisting of the bald eagle, impacts from
livestock grazing on streams will continue to be minimized through
consultations conducted for those other species and their designated
critical habitats. Along many portions of the Verde River and Tonto
Creek, livestock grazing has currently been discontinued. Riparian
recovery, at least in response to a reduction in grazing pressure, may
therefore be underway in some of these areas. Improper livestock
grazing may still be an added stressor on those systems where it
continues to occur (absent a separately listed species), where trespass
or unauthorized cattle are grazing, or where habitat is already
degraded due to other factors.
In Mexico, while the magnitude and significance of adverse effects
to riparian communities related to development lags behind the United
States due to slower population and economic growth, impacts to
riparian and aquatic communities are currently occurring with
increasing significance (Conant 1974, pp. 471, 487-489; Contreras
Balderas and Lozano 1994, pp. 379-381; va Landa et al. 1997, p. 316;
Miller et al. 2005, pp. 60-61; Abarca 2006, pers. comm.; Rosen 2006,
pers. comm.). Mexico's population increased by 245 percent from 1950 to
2002, and is projected to grow by another 28 percent by 2025
(EarthTrends 2003, pp. 1-2). As a result of the North American Free
Trade Agreement, the number of maquiladoras (export assembly plants) is
expected to increase by as many as 3,000 to 4,000 (Contreras Balderas
and Lozano 1994, p. 384). To accommodate Mexico's increasing human
population, rural areas are largely devoted to food production based on
traditional methods, which has led to serious losses in vegetative
cover and soil erosion (va Landa et al. 1997, p. 316). In addition,
changes in land legislation within Mexico related to free market
policies and local agricultural production methods may result in the
loss of land management practices that protect the natural environment
(Ortega-Huerta and Kral 2007, p. 1). Much of the riparian woodland in
the broad floodplains along the Rio Bavispe has been cleared for
agriculture and pasturelands. Similarly, portions of the riparian
habitat along the Rio Yaqui have also been affected by agriculture, and
heavy livestock grazing has occurred throughout the Rio Yaqui and Rio
Bavispe (Brown et al. 1986, pp. 3, 5). In one breeding area along the
Rio Yaqui, the nest failed in 1986 due to the construction of a fence
in preparation for agricultural development. The nest was then
destroyed in 1987 as a result of a fire set to clear the land for
agriculture (Driscoll and Mesta 2005, in prep.).
Several recent development projects in Mexico have affected bald
eagle breeding areas. In 1998, a new road was created from the Town of
Sahuaripa to the Rio Yaqui/Sahuaripa confluence, which was followed by
a cement property marker placed above the eagle's cliff nest in 1999
(Driscoll and Mesta 2005, p. 58). From 2000 to 2002, construction and
completion of a new highway bridge occurred immediately at the
Sahuaripa bald eagle nest, which had formerly been the most successful
mainland Sonora bald eagle territory. Associated with the bridge
construction, development of worker living quarters, an equipment
staging area, and a construction material borrow site near the nest
resulted in further habitat degradation. The placement and development
of the new road and bridge generated increased human activity (e.g.,
fishing, swimming, picnics), and development of four ranch buildings in
the Sahuaripa breeding area. In 2009, this pair was located in the
vicinity of the Sahuaripa breeding area, and it is likely that they
have relocated to a new site below the bridge (Mesta 2009, pers.
comm.).
Despite the increase in human population and associated impacts to
the riparian habitat on which the bald eagle depends, the known number
of breeding areas within the Sonoran
[[Page 25816]]
Desert Area has increased from a low of three in 1971 to a high of 52
in 2009, and the population has expanded into areas not previously
occupied. As a result of this growth, the density of breeding areas
along sections of the Salt and Verde Rivers has increased in recent
years. AGFD survey data showed that the bald eagle population in
Arizona continued to grow during approximately the same time period
that Arizona experienced a 394 percent increase in human population
(e.g., from 1960 to 2000). While the magnitude of the effects described
above may be moderate in localized areas, they are not occurring at all
breeding areas or throughout the range of the Sonoran Desert Area
population of the bald eagle. In addition, the eagle population has
continued to increase at the same time that urbanization and the loss
of riparian habitat have increased. Therefore, the urbanization and
loss of riparian habitat are not affecting bald eagles at such a scale
or magnitude that they constitute a threat at the population level.
At this time, there is no indication of additional or new impacts
to riparian areas that would accelerate or increase the current
pressures to riparian habitat beyond what is currently occurring. Based
upon what we know about how impacts to these key features can affect
bald eagles, it would not be unreasonable to anticipate that if there
is continued degradation of habitat, especially key features such as
trees, at some point reproductive performance or breeding area
occupancy could be affected. At what point and to what extent continued
human population growth, associated resource use, and degradation of
riparian habitat will manifest itself in effects to the Sonoran Desert
Area population of the bald eagle is unknown. Unlike species with a
narrow habitat requirement, the bald eagle uses broader landscapes, and
as a result, some change to habitat is not expected to impede their
ability to adjust and use the available landscape features
successfully. As a result, the best available information does not
suggest the increase in human population occurring in Arizona now and
predicted to continue into the future will result in declines to the
Sonoran Desert Area population of the bald eagle.
Loss of Surface Flows From Groundwater Pumping and Surface Water
Diversions
Increased urbanization and population growth also results in an
increase in the demand for water and, therefore, water development
projects. American Rivers (2006, p. 30) found that municipal water use
in central Arizona increased by more than 39 percent between 1998 and
2006, and that the demand for water will only increase as the human
population increases. Water for development and urbanization is often
supplied by groundwater pumping and surface water diversions from
sources that include reservoirs and Central Arizona Project's (the
steward of central Arizona's Colorado River water entitlement)
allocations from the Colorado River. The impacts of groundwater pumping
on surface water flows are of particular concern along the Salt and
Verde Rivers (University of Arizona 2004, p. 69), as well as the Gila
River, all of which occur within the Sonoran Desert Area. Most of the
recent bald eagle breeding areas have become established along the Salt
and Verde Rivers (Allison et al. 2008, pp. 17-18), and elimination of
key habitat elements (e.g., water, prey base, large trees) could affect
the ability of bald eagles to continue to reproduce and expand along
these river systems.
The Verde River was identified as one of the country's most
endangered rivers of 2006 (American Rivers 2006, pp. 30-31) due to
groundwater pumping. As a result of rapidly growing communities in
Arizona, groundwater pumping has caused portions of the Verde River to
have limited or no flow during portions of the year (Stromberg et al.
1996, pp. 113, 124-128; Rinne et al. 1998, p. 9; Voeltz 2002, pp. 45-
47, 69-71). Specifically, more than 6 miles of perennial stream
segments on the Verde River have been lost since approximately 1950,
and water levels near Sullivan Lake in the headwaters of the Verde
River have declined by greater than 80 feet since 1947 (Wirt 2006, pp.
5-6).
Because of increasing demands for water and decreasing groundwater
levels, the State Legislature adopted the Arizona Groundwater
Management Act (A.R.S. Sec. 45-555) in 1980. The Arizona Groundwater
Management Act designated four Active Management Areas where
groundwater supplies are critical or imperiled for whole or multiple
groundwater basins. The Arizona Groundwater Management Act limits
existing uses of groundwater within an Active Management Area, and
restricts new uses (Marder 2009, p. 183). The City of Prescott is out
of compliance with the Arizona Groundwater Management Act, and, in
order to achieve compliance, has had to secure new resources, teaming
up with Prescott Valley in developing a plan to pump water from the Big
Chino Aquifer. This plan and the associated well field development and
water transfer is commonly known as the Big Chino Ranch Project. In
1992, the Arizona Legislature adopted A.R.S. 45-555(E), which
explicitly authorizes the City of Prescott to pump up to 14,000 acre-
feet per year from the Big Chino Aquifer. In addition, the town of
Chino Valley has plans for their own groundwater pumping, which would
be located in the Big Chino aquifer, and would allow the development of
approximately 20,000 new homes (Marder 2009, pp. 183-187).
Many scientists, conservationists, and water providers, such as the
Salt River Project, are in agreement that groundwater pumping has
already had an impact on the Verde River and that--given the plans of
Prescott, Prescott Valley, and Chino Valley--further reductions in the
Verde River instream flows are inevitable (Marder 2009, p. 187). The
proposed groundwater pumping and inter-basin transfer project is
projected to deliver 2.8 billion gallons of groundwater annually from
the Big Chino sub-basin aquifer to the rapidly growing area of Prescott
Valley for municipal use (McKinnon 2006, p. 1). It is estimated that 80
to 85 percent of base flow in the upper Verde River comes from the Big
Chino aquifer, and it is possible that that these groundwater
withdrawals could dewater the upper 24 miles of the Verde River (Wirt
and Hjalmarson 2000, p. 44; Wirt 2005, p. G7; Blasch et al. 2006,
updated 2007, pp. 1-2). The loss of water on the upper Verde River
would affect fish populations and consequently productivity in at least
one bald eagle breeding area (Driscoll et al. 2006, p. 15).
The effects of large-scale groundwater pumping associated with the
proposed Big Chino Water Ranch Project and its associated 30-mile
pipeline have yet to be realized in the Verde River. It is uncertain
that this project will occur given the legal and administrative
challenges it faces; however, Prescott, Prescott Valley, and Chino
Valley have invested millions of dollars in planning and property
acquisition, and the pumping has already been authorized by State law.
In 2009, a Memorandum of Understanding was signed between the Town of
Chino Valley and the Service that may help to mitigate some of the
impacts of their groundwater withdrawals in the future. The Town of
Chino Valley has agreed that, as it develops its water development
plan, it will confer with the Service to assess potential impacts to
the Verde River and its native species and habitats, and will cooperate
with the Service to remove or reduce impacts (Service 2009, p. 2).
[[Page 25817]]
Additional groundwater withdrawal projects that may affect the Verde
River include developments associated with the proposed consolidation
of checkerboard land ownership in the Big Chino Valley. Authorized by
Title I of Public Law 109-110 in November 2005, the Yavapai Ranch
Limited Partnership will acquire 15,400 acres of land within Prescott
National Forest in the Big Chino Valley, consolidating private
ownership of 30,440 acres. At full buildout, the development could
result in water use of an additional 1,039 acre-feet pumped from the
Big Chino aquifer. Existing groundwater withdrawals for the Big Chino
sub-basin between 1990 and 2003 averaged 11,840 acre-feet (Blasch et
al. 2006, updated 2007, p. 82). Those withdrawals--in conjunction with
proposed pumping from the City of Prescott, Town of Prescott Valley,
and the Yavapai Ranch--would exceed the total rate of recharge to the
Big Chino aquifer of approximately 21,500 acre-feet.
The middle Verde River has experienced low flows that have at times
resulted in only 5,982 acre-feet of runoff into Horseshoe reservoir,
considerably less than the normal of 7,478 acre-feet (Verde Natural
Resources Conservation District 1999, p. 1). Multiple diversions and
groundwater pumping are likely contributing to low flows in this
portion of the Verde River (Miller 1961, pp. 398-399; Owen-Joyce and
Bell 1983, pp. 33-37; Sullivan and Richardson 1993, pp. 96, 124;
Stromberg 1993, p. 101; Glennon and Maddock 1994, pp. 578-585; Glennon
1995, pp. 133-134; Tellman et al. 1997, pp. 46-49).
In Tonto Creek, which feeds into Roosevelt Lake on the Salt River,
groundwater pumping is one of the factors that contribute to a loss of
surface flows during part of the year between the winter and spring
runoff and summer monsoon (Abarca and Weedman 1993, p. 2). However,
Tonto Creek supports only two bald eagle breeding areas, both of which
continue to produce young on a regular basis. In addition, the adults
from one of these breeding areas may acquire additional resources from
Roosevelt Lake during years of high water or during the winter (Service
2003, p. 63).
Groundwater pumping has also led to identification of the Gila
River as the nation's seventh most endangered river in 2008 (American
Rivers 2008, p. 33). Congress, through the Arizona Water Rights
Settlement Act of 2004 (Pub. L. 108-451, 118 Stat. 3478, December 10,
2004), allocated up to $128 million for implementation of water
projects designed to meet New Mexico's future water needs (NMISC 2006,
pp. 6-7). The State of New Mexico must provide notice to the Secretary
of the Interior by December 2014 whether or not it will use the
allocation to develop water projects.
The New Mexico Interstate Stream Commission has proposed a project
that would divert up to 14,000 acre-feet of water from the Gila River
and its tributary, the San Francisco River, annually. The project would
also require a diversion structure, pumping station, power station, a
pipeline or canal system, and potentially an offsite dam and reservoir.
The amount of water diverted would negatively affect groundwater wells,
impair the river's natural flows, impede the growth of riparian
vegetation, and negatively affect native fish and birds (American
Rivers 2008, p. 33). While existing water rights of the San Carlos
Apache Tribe would ensure that adequate flows remain in the Gila River
to allow for the San Carlos Reservoir in Arizona to be at least
partially filled, a reduction in flows would mean that less water would
be available for storage in the reservoir, and, consequently, less
water would be released from the reservoir into areas on the Gila River
downstream of the reservoir.
Decreased flows from the reservoir could negatively affect the prey
base (fish) and habitat for the three bald eagle breeding areas located
downstream. However, it is important to note that the adults at only
two of these breeding areas rely solely on free-flowing sections of the
Gila River for foraging resources, and neither of them has ever
produced young (Allison et al. 2008, pp. 17-18). The adults at the
third breeding area use the San Carlos Reservoir as their primary
foraging area and are less likely to be affected by decreased flows in
the Gila River.
The construction and management of reservoirs may result in adverse
effects to the river ecosystem. However, the presence of reservoirs,
dams, or regulated river reaches did not appear to have a negative
effect on bald eagle reproduction in a sample of 21 bald eagle
territories studied in Arizona in the 1980's (Hunt et al. 1992, p. A-
iv). The presence and management of reservoirs can lead to sediment
entrapment, reductions in total annual flow and annual flood peaks,
changes in the timing and size of high and low flows, altered surface
area due to water releases, and altered short-term fluctuations. These
in turn cause changes to plant species, including a loss of some
species, and a decrease in recruitment of new vegetation (Service 2002,
pp. I9-I12). However, eagle populations have not been shown to decline
as a result of reservoirs, and may even benefit over the long term. For
example, some reservoir storage has also created habitat for bald
eagles in places where they may not have occurred, even before large-
scale human development. Reservoirs provide additional habitat
diversity, especially in a desert ecosystem, and may create a more
stable food source for bald eagles during the winter months due to
congregations of waterfowl. The creation of reservoirs usually
coincides with the introduction of exotic species of fish, some of
which (e.g., catfish, bass, carp) can deplete native fishes. However,
these exotic species make up a large portion of bald eagle diets in the
Sonoran Desert Area, both in Arizona and Sonora (Hunt et al. 1992, pp.
A25-A26; Hunt et al. 2002, pp. 249-251).
Similarly, eagle populations do not necessarily decline as a result
of changes in vegetation due to the presence or management of
reservoirs. Downstream from reservoirs, regulated flows have caused
declines of riparian cottonwood and willow forests throughout the
western United States (Service 2002, p. I12). The timing of water
releases from many dams has also impeded riparian regeneration,
destroyed riparian habitat and stream banks, and can influence the
abundance, distribution, and diversity of fish species (Stromberg et
al. 1996, p. 114; Poff et al. 1997, pp. 769-770). Although the
persistence of riparian trees is not a management concern in most
breeding areas upstream of dams or where appropriate cliffs are
available, within some breeding areas located below dams, existing
trees have become old, are dying, and are not being replaced (AGFD
2008, p. 9). This is in part due to modification of flood regimes by
dams, which leads to a lack of sediment deposition, seed dispersal, and
timing of flows adequate for seed germination.
When reservoir management leads to reduced surface area by
releasing water and lowering the level of the reservoir, bald eagles
established there may have fewer perches for foraging, loafing,
feeding, and display (Stalmaster 1987). Similar impacts may also occur
in Mexico, where water for agriculture is supplied through dams,
specifically timed water releases, diversions, and surface water
pumping (Driscoll and Mesta 2005, in prep.). Inundation from dams and
reservoirs can have similar impacts, and can also eliminate spawning
fish runs and remove nest sites, foraging areas, and gravel bars that
accumulate carrion (Hunt et al. 1992, p. A46). The continuous drop of
lake
[[Page 25818]]
levels at Roosevelt Lake from almost 100 percent storage capacity to
near 10 percent between 1993 and 2001 was shown to have a negative
effect on productivity at five bald eagle breeding areas that relied on
the lake for foraging resources (Service 2003, pp. 65-67). Yet even
with the drop in lake size, occupancy rates remained high, and young
continued to be produced from the affected breeding areas. On the Verde
River below Bartlett Reservoir, the release of cold water from the
reservoir and other management activities contributed to this area's
having the greatest increase in the number of bald eagle breeding areas
in Arizona from 1994 to 2002 (Service 2003, pp. 72-73). Therefore, the
best available information suggests that reservoir management may
result in short-term, localized impacts to some bald eagle breeding
areas in the Sonoran Desert Area by negatively affecting productivity,
but these impacts are not resulting in a reduction of the eagle
population.
Congress passed the Arizona Water Settlement Act approving the Gila
River Indian Community Water Rights Settlement Agreement in 2004. In
2005, the Secretary of the Interior signed the Gila River Indian
Community Water Rights Settlement Agreement confirming the Community's
claim to 653,500 acre-feet of water per 10-year period, providing
Federal funding for water development projects, assuring rights to use
existing water delivery systems, and adding protections for the
Community's groundwater supplies (DOI 2005, p. 4; ADWR 2006, p. 3-2).
Potential projects to be developed, and the impacts any projects are
likely to have on the Gila River, are not yet known; however, passage
of the law in 2004 and development of the Gila River Indian Community
Water Rights Settlement Act make certain that some level of diversion
or pumping will occur in the future. We do not anticipate that such
projects would have a population-level effect on the Sonoran Desert
Area bald eagle population. As mentioned above, there are only two bald
eagle breeding areas that rely solely on free-flowing sections of the
Gila River for foraging resources, and neither of them has ever
produced young (Allison et al. 2008, pp. 17-18).
In the Sonoran Desert Area, flood control has led to
channelization, bank stabilization, and levees. These engineering
activities affect riparian systems by preventing overbank flooding,
reducing the extent of the floodplain, reducing water tables adjacent
to streams, increasing stream velocity and the intensity of extreme
floods, and generally reducing the volume and width of wooded riparian
habitats (Szaro 1989, pp. 77-80; Poff et al. 1997, pp. 769-770).
Southwestern streams are known for their ``flashy'' (i.e., rapid
changes in water levels following heavy rains) hydrology. In the past
30 years, 100-year flood events have occurred twice in Arizona, in 1983
and 1993. Other major floods occurred in Arizona in 1926, 1942, 1962,
1966, 1970, and 1974 (Arizona Geological Survey 1984, p. 1; USGS 1989,
pp. 1-2; Arizona Geological Survey 1993, p. 1). This flooding history
may be an indication that similar events are likely to occur in the
Sonoran Desert Area in the foreseeable future, and, as a result, flood
control measures will also likely continue to be implemented. These
flood control measures and their associated impacts to riparian systems
can decrease the amount of suitable habitat available to bald eagles
for perching and nesting. On the other hand, the creation of berms,
dams, and diversions has benefited some breeding pairs of bald eagles
in the Sonoran Desert Area by making prey species more available, but
these activities, in addition to water table pumping on rivers and
creeks with limited flow, could at the same time be making prey species
less available by reducing the size of bald eagle foraging areas
(Driscoll et al. 2006, pp. 14-15).
A decrease in, or complete loss of, surface flows within portions
of the Verde, Salt, or Gila Rivers could result in a loss of riparian
habitat and a reduction or loss of prey (e.g., fish) at a localized
level (for the affected breeding areas). The breeding areas associated
with the Verde River are responsible for 22 percent of the total
productivity within the Sonoran Desert Area. Because of the importance
of river systems, particularly the Verde River, to the Sonoran Desert
Area population of the bald eagle, accurately quantifying the potential
effects of lost surface flows at the population level would be
valuable. Statistical methods can be used to quantitatively estimate
population growth and extinction probabilities for a species under
different demographic and environmental scenarios. The simplest type of
model to perform this can be referred to as a simple population
viability analysis (PVA). A simple PVA quantitatively estimates
population growth and extinction probabilities for a single population
(Dennis et al. 1991, p. 116). The only PVA analyzing the potential
impacts from the loss of surface flows to the Sonoran Desert Area
population of the bald eagle was conducted in 2009. The Service used a
PVA to analyze the potential impact that complete loss of surface flows
on the upper Verde River would have on bald eagles breeding in the
Sonoran Desert Area of Arizona. The preliminary results of this
analysis indicated that, even with the hypothetical loss of breeding
areas along the Verde River, the bald eagle population as a whole would
remain stable (Millsap 2009, in prep.). This suggests that the loss of
surface flows within portions of the Verde River may be a threat of
moderate magnitude at a localized or regional scale, but the impact to
Sonoran Desert Area bald eagles at the population level is predicted to
be low.
Summary of Factor A
The Service has identified potential threats to the Sonoran Desert
Area population of the bald eagle from the present or threatened
destruction, modification, or curtailment of the Sonoran Desert Area
population of the bald eagle. These threats include the degradation and
loss of riparian habitat and the loss of surface flows from groundwater
pumping and surface water diversions. There is little doubt that the
human population in Arizona, specifically within areas occupied by bald
eagles, will continue to grow into the future. Associated with this
growth, there will likely be an increase in development and
modifications to some of the habitat on which bald eagles depend for
nesting, roosting, perching, and foraging.
Although available information indicates that urban and rural
development, livestock grazing, groundwater pumping, and surface water
diversions have likely resulted in historical and continued loss of
habitat and negative impacts to specific breeding areas or individual
eagles, there is no indication that ongoing impacts are affecting the
Sonoran Desert Area population of the bald eagle at the population
level. Thus, they are not significantly contributing to the risk of
extinction of the population.
B. Overutilization for Commercial, Recreational, Scientific, or
Educational Purposes
We do not have any evidence of risks to the Sonoran Desert Area
population of the bald eagle from overutilization for commercial,
scientific, or educational purposes, and we have no information to
indicate that this factor will become a threat to the species in the
future.
C. Disease or Predation
We do not have any evidence of risks to the Sonoran Desert Area
population
[[Page 25819]]
of the bald eagle from disease or predation, and we have no information
to indicate that this factor will become a threat to the species in the
future.
D. Inadequacy of Existing Regulatory Mechanisms
Under this factor, we examine whether existing regulatory
mechanisms are inadequate to address the threats to the Sonoran Desert
Area population of the bald eagle discussed under Factors A and E.
Section 4(b)(1)(A) of the Endangered Species Act requires the Service
to take into account ``those efforts, if any, being made by any State
or foreign nation, or any political subdivision of a State or foreign
nation, to protect such species * * *.'' We interpret this language to
require the Service to consider relevant Federal, State, and Tribal
laws, plans, regulations, Memoranda of Understandings (MOUs),
Cooperative Agreements, and other such mechanisms that may minimize any
of the threats we describe in threat analyses under all five factors,
or otherwise enhance conservation of the species. We give strongest
weight to statutes and their implementing regulations, and management
direction that stems from those laws and regulations. An example would
be the terms and conditions attached to a grazing permit that describe
how a permittee will manage livestock on a BLM allotment. They are
nondiscretionary and enforceable, and are considered a regulatory
mechanism under this analysis. Other examples include State
governmental actions enforced under a State statute or constitution, or
Federal action under statute. Some other agreements (MOUs and others)
are more voluntary in nature; in those cases we analyze the specific
facts for that effort to ascertain the extent to which it can be relied
on in the future, and how effective it is, and will continue to be, at
mitigating the threat.
Having evaluated the significance of the threat as mitigated by any
such conservation efforts, we analyze under Factor D the extent to
which existing regulatory mechanisms are inadequate to address the
specific threats to the species. Regulatory mechanisms, if they exist,
may preclude the need for listing if we determine that such mechanisms
adequately address the threats to the species such that listing is not
warranted. Within its distribution in the Sonoran Desert Area, the bald
eagle occurs on lands managed by a myriad of Federal and State
agencies, Native American tribes, local municipalities, and private
lands. In this section, we review existing State and Federal regulatory
mechanisms to determine whether they effectively reduce or remove
threats to the Sonoran Desert Area population of the bald eagle.
Specifically, the regulatory mechanisms discussed below address some of
the effects to bald eagles from the direct take of individuals, as well
as the indirect take through disturbance, loss of riparian habitat, and
development.
Federal laws and regulatory mechanisms protecting bald eagles
throughout the United States include the Migratory Bird Treaty Act
(MBTA, 16 U.S.C. 703-712), Bald and Golden Eagle Protection Act (BGEPA,
16 U.S.C. 668 et seq.), Executive Order 13186, the Lacey Act Amendments
of 1981 (16 U.S.C. 3372-3378), Section 404 of the Clean Water Act (CWA,
33 U.S.C. 1251 et seq.), Fish and Wildlife Coordination Act (16 U.S.C.
661-666c), National Environmental Protection Act (NEPA, 42 U.S.C. 4321
et seq.) and the Convention on International Trade in Endangered
Species of Wild Fauna and Flora (CITES). For more information regarding
these regulatory mechanisms, please refer to the February 16, 2006,
Federal Register notice (71 FR 8238) reopening the comment period on
the proposed rule to delist the bald eagle in the lower 48 States.
Below we summarize the protections provided to bald eagles under the
NEPA, MBTA, BGEPA, and CWA.
All Federal agencies are required to comply with NEPA for projects
they fund, authorize, or carry out. Additionally, activities on non-
Federal lands are subject to NEPA if there is a Federal nexus, such as
permitting by the U.S. Army Corps of Engineers or the Federal Energy
Regulatory Commission. The Council on Environmental Quality's
regulations for implementing NEPA (40 CFR parts 1500-1518) state that
environmental impact statements shall include a discussion on the
environmental impacts of the various project alternatives (including
the proposed action), any adverse environmental effects that cannot be
avoided, and any irreversible or irretrievable commitments of resources
involved (40 CFR part 1502). The NEPA itself is a disclosure law that
provides an opportunity for the public to submit comments on the
particular project and propose other conservation measures that may
directly benefit listed or sensitive fish and wildlife species;
however, it does not require subsequent minimization or mitigation
measures by the Federal agency involved. Although Federal agencies may
include conservation measures for listed species as a result of the
NEPA process, there is no requirement that impacts to the Sonoran
Desert Area population of the bald eagle from actions analyzed under
NEPA would be precluded. Any such measures are typically voluntary in
nature and are not required by the statute.
The MBTA implements various treaties and conventions between the
United States and other countries and, unless permitted by regulations,
it provides that it is unlawful to pursue; hunt; take; capture; kill;
possess; offer to sell, barter, purchase, deliver; or cause to be
shipped, exported, imported, transported, carried, or received any
migratory bird, part, nest, egg, or product, manufactured or not. The
BGEPA, originally passed in 1940, prohibits the take, possession, sale,
purchase, barter, offer to sell, purchase, or barter, transport, export
or import, of any bald or golden eagle, alive or dead, including any
part, nest, or egg, unless allowed by permit. ``Take'' is defined as to
``pursue, shoot, shoot at, poison, wound, kill, capture, trap, collect,
molest or disturb'' a bald or golden eagle. To provide a consistent
framework in which to implement the BGEPA after bald eagle delisting,
on June 5, 2007, the Service clarified its regulations implementing the
BGEPA (72 FR 31132). These modifications to the implementing
regulations for the BGEPA established a regulatory definition of
``disturb,'' a term specifically prohibited as ``take'' by the BGEPA.
As per the regulatory definition, ``disturb'' means to ``agitate or
bother a bald or golden eagle to a degree that causes, or is likely to
cause, based on the best scientific information available, injury to an
eagle; a decrease in its productivity, by substantially interfering
with normal breeding, feeding, or sheltering behavior; or nest
abandonment, by substantially interfering with normal breeding,
feeding, or sheltering behavior.'' The BGEPA was initially designed to
protect eagles from intentional take, and lawfully permit intentional
take for such purposes as education, depredation, research, and Native
American religious purposes. However, the regulatory definition of
``disturb'' described above may have the added benefit of providing
indirect protection of bald eagle habitat (e.g., if destruction of
habitat results in disturbance).
In 2009, the Service promulgated new permit regulations under the
authority of the BGEPA for the limited take of bald eagles and golden
eagles ``for the protection of * * * other interests in any particular
locality'' where the take is compatible with the preservation of
[[Page 25820]]
the bald eagle and the golden eagle, is associated with and not the
purpose of an otherwise lawful activity, and cannot practicably be
avoided (74 FR 46836). The Service has interpreted ``compatible with
the preservation of the bald and golden eagle'' to mean allowing take
that is consistent with the goal of stable or increasing breeding
populations. We will evaluate permit applications based on whether: (1)
The take is necessary to protect a legitimate interest in a particular
locality; (2) the take is associated with, but is not the purpose of
the activity; (3) the take cannot practicably be avoided (or for
programmatic authorizations, the take is unavoidable); and (4) the
applicant has minimized impacts to eagles to the extent practicable,
and for programmatic authorizations, the taking will occur despite
application of Advanced Conservation Practices developed in
coordination with the Service. Although the effects of implementing
these regulations have not been realized, the Service's goal of a
stable or increasing breeding population of bald and golden eagles
indicates a commitment to their conservation and management into the
future.
As discussed earlier in this document, bald eagle activities such
as nesting, perching, roosting, and foraging in the Sonoran Desert Area
occur from and in the large woody tree component of the riparian
habitat found along rivers and streams, and section 404 of the CWA
regulates fill in wetlands and streams that meet certain jurisdictional
requirements. Activities that result in fill of jurisdictional wetland
and stream habitat require a section 404 permit. The Service can review
permit applications and provide recommendations to avoid and minimize
impacts and to implement conservation measures for fish and wildlife
resources, including the bald eagle. However, incorporation of Service
recommendations into section 404 permits is at the discretion of the
U.S. Army Corps of Engineers. In addition, not all activities in
wetlands or streams involve fill, and not all wetlands or streams fall
under the jurisdiction of the U.S. Army Corps of Engineers. Regardless,
earlier in this finding we evaluated threats to the Sonoran Desert Area
population of the bald eagle where effects to riparian habitat may
occur. We found no information indicating that the degradation or loss
of riparian habitat is acting on the species to the point that the
species itself may be at risk, nor is it likely to become so in the
future.
In Mexico, the bald eagle is listed at the species level as ``En
Peligro de Extincion,'' or In Danger of Extinction, by the Secretaria
de Medio Ambiente y Recursos Naturales (SEDESOL 2001, p. 20). Species
in danger of extinction are ``those whose areas of distribution or size
of their populations in the national territory have diminished
drastically putting at risk their biological viability in their entire
natural habitat, due to factors such as the destruction or drastic
modification of the habitat, unsustainable exploitation, disease or
depredation, among others'' (SEDESOL 2001, p. 4). This classification
coincides partly with the International Union for Conservation of
Nature's categories of ``in critical danger'' and ``in danger of
extinction.'' This designation prohibits taking of the species, unless
specifically permitted, as well as any activity that intentionally
destroys or adversely modifies its habitat. Additionally, in 1988, the
Mexican Government passed the General Law of Ecological Equilibrium and
Environmental Protection that is similar to NEPA in the United States.
This Mexican statute requires an environmental assessment of private or
government actions that may affect wildlife or their habitat. However,
while these laws in Mexico prohibit intentional destruction or
modification of the bald eagle's habitat, they do not appear to be
adequate to preclude impacts to the species' habitat. Currently, we
know of no regulatory mechanisms or conservation planning in place that
specifically targets the conservation of bald eagle habitat in Mexico.
Legislation in Mexico has removed regulations that promoted intact
protection of important riparian and aquatic habitats. Based upon the
lack of conservation detected through existing regulations over the
last 20 years of monitoring bald eagles in the mainland of Sonora, we
anticipate there will continue to be future limitations to the
regulatory mechanisms in Mexico.
Despite concerns expressed through an apparent lack of adequate
protection for the bald eagle in Mexico, Federal regulatory mechanisms
in place in the Sonoran Desert Area in Arizona, where most of the
breeding areas are located, appear to be adequate to alleviate some of
the threats to the population. The apparent lack of protection for bald
eagles in Mexico may contribute to localized or regional impacts to
bald eagle breeding areas in that country. However, these impacts only
have the potential to affect the eight known breeding areas located in
Mexico, which would not be sufficient to result in impacts at the
population level.
Summary of Factor D
The Sonoran Desert Area population of the bald eagle is protected
by many Federal laws and other regulatory mechanisms. Whether or not
the population is listed under the ESA, the take of bald eagles in the
United States--including the Sonoran Desert Area population--will
continue to be prohibited under the MBTA, BGEPA, and the Lacey Act.
While legislation in Mexico prohibits intentional destruction or
modification of the bald eagle's habitat, and prohibits take, the
legislation does not appear to be adequate to preclude impacts to the
species' habitat. Nevertheless, even if this apparent lack of
protection for habitat has impacts upon the bald eagles in Sonora,
those impacts would only be localized or regional in scope, and would
not affect the Sonoran Desert Area bald eagle as a population level.
After reviewing the best available commercial and scientific
information, we conclude that the inadequacy of existing regulatory
mechanisms does not significantly contribute to the risk of extinction
of the Sonoran Desert Area population of the bald eagle, because the
bald eagle is protected by many Federal laws and other regulatory
mechanisms and our analysis of Factors A and E concluded that there are
no significant threats to the population.
E. Other Natural or Manmade Factors Affecting Its Continued Existence
Demographic Factors
Three different demographic models have been completed for the bald
eagle in Arizona; two of those models specifically analyzed only those
bald eagles nesting in the Sonoran Desert Area of Arizona (Allison et
al. 2008, pp. 26-38; Silver and Taylor 2008, pp. 17-25; and Millsap
2009, in prep.). The analysis associated with the first model
estimated, based on resightings of eagles at breeding areas, that
juvenile mortality increased substantially over the period of time
between 1975 and 2007. If juvenile mortality is at the high levels
estimated and it stays at those levels, the model estimated the
probability of extinction for the Sonoran Desert Area population of the
bald eagle in Arizona by 2075 at 69.5 percent. This analysis assumed
that juvenile mortality would continue to occur unabated at that level
and concluded that, should fish stocking on the Salt and Verde Rivers
be decreased or the management efforts carried out under the ABENWP be
discontinued, the probability of extinction would be even higher.
However, if juvenile mortality could be reduced to the average
mortality value of the entire period of study, the extinction risk
would be reduced to four
[[Page 25821]]
percent by 2075 (Silver and Taylor 2008, pp. 2, 25-26, 52-55).
In the Arizona-wide model, the AGFD conducted its own demographic
analysis of the bald eagle in Arizona in 2008. This analysis
incorporated data from all breeding areas in Arizona, including six
that were located outside of the Sonoran Desert Area. The model
developed by the AGFD concluded that--depending on the age at first
reproduction, sex ratios, and the proportion of females that breed each
year--future annual declines in breeding will likely range between 3.6
and 5.5 percent. This is consistent with a stable or declining
population (Allison et al. 2008, p. ii). In the same analysis however,
simple counts of bald eagles breeding in Arizona each year indicated
that the breeding segment has been increasing at an average rate of 4.0
percent per year from 1987 to 2003 (Allison et al. 2008, p. 26). The
discrepancies between the demographic model and the count-based
estimates may reflect incorrect assumptions about newly discovered
breeding areas, idiosyncrasies of their data, low estimates of
survival, emigration, shifting age of first reproduction from an
expanding population, or recruitment of breeders from unmarked
populations. The AGFD concluded that their work did not determine
whether or not the bald eagle population in Arizona, including the
Sonoran Desert Area, was stable, but instead identified gaps in data
that limit the ability to accurately predict population stability
through demographic models (Allison et al. 2008, pp. ii, 30-31).
The Service reviewed the above-mentioned models conducted by the
AGFD and Silver and Taylor (2008, pp. 17-26). A concern with these
models is that both have led to estimates of the annual rate of
population change (or replacement rate ([lambda])) that are less than
1.0, indicative of a declining population, whereas actual counts of
occupied territories have increased almost annually since 1983 (Allison
et al. 2008, p. 20). Although there are many factors that might
contribute to this discrepancy, the Service believes the most likely
factor is that juvenile and subadult bald eagle survival is
underestimated. Underestimation of survival rates for nonbreeding age
classes and cohorts of raptors in mark-recapture studies is common
(Kenward et al. 2000, p. 277; Millsap and Allen 2006, p. 1396), and
both Silver and Taylor (2008, p. 24) and Allison et al. (2008, pp. 14,
33) recognized this as a possible reason for the incongruence between
model-based results and reality. This can bias results from the fact
that most detections of marked bald eagles occur once birds settle on a
territory and begin breeding. Bald eagles marked as nestlings do not
typically settle on a territory for 4 years or longer, and
probabilities of detection are confounded by potential for long-
distance natal dispersal, rates of which may differ between the sexes.
As evidence of the potential that this bias exists for the Arizona
study, the juvenile and subadult annual survival rate for the selected
model in Allison et al. (2008) was 73 percent. Annual survival
estimates from studies employing radio or satellite telemetry, which do
not have the same resighting bias for juvenile and subadult bald
eagles, ranged from an average of 95 percent in Virginia (Buehler et
al. 1991, pp. 610-611), to 85 percent (Wood and Collopy 1995, pp. 83-
85) in one Florida study and 84 percent in another (Millsap et al.
2004, pp. 1025-1027).
The Service has concerns about using model results that are
inconsistent with known historic population trajectories to evaluate
extinction risk. However, we believe it is reasonable to conclude that
biased juvenile and subadult survival rates are the main reason for the
discrepancy, and a logical fix is to iteratively adjust these rates
until the annual rate of population change reaches the observed value
and then to evaluate extinction risk using models that incorporate
these demographic estimates. Using the adjusted survival rates, in 2009
the Service developed a third model, which specifically analyzed the
Sonoran Desert Area population of bald eagles in Arizona (Millsap 2009,
in prep.). For the baseline model, productivity was set at 0.76,
nonadult survival (i.e., fledgling to age four) was set at 0.805, adult
survival was set at 0.88, and the number of suitable breeding
territories was set at 42. Under this scenario, none of the 100
iterations in the model resulted in extinction, and the annual rate of
population change was equal to 1.02 (i.e., the population was growing
at an annual rate of 2 percent) (Millsap 2009, in prep.).
Mortality rates of bald eagles in Arizona appear to be consistent
with those reported for other populations of bald eagles. An average of
16 percent adult mortality was reported between 1987 and 1990 (5.25
breeding adults annually) (Hunt et al. 1992, p. A137) for bald eagles
in Arizona. This mortality rate is within the range reported for other
populations, which ranged from 5 to 17 percent (Allison et al. 2008, p.
25). Nestling mortality rates of 22.6 and 25 percent have been reported
in Arizona (Driscoll et al. 1999, p. 222; Allison et al. 2008, p. 33).
In mainland Sonora, over 20 years of monitoring, 14 nestlings died (26
percent) of the 54 nestlings known to have hatched (Driscoll and Mesta
2005, in prep.). These rates are higher than the 15 percent reported in
rangewide studies (Stalmaster 1987, p. 143). However, the higher rate
of mortality reported in Arizona may be in part attributable to more
intensive monitoring and consequently better detection of mortalities
through the ABENWP. Subadult survival in Arizona is generally lower
than that reported elsewhere, but this should be considered apparent
survival, since estimates may include losses due to emigration as well
as mortality.
Two adult bald eagles and two nestlings were discovered dead below
nests within the mainland Sonora population in 1988 and 1993 (Driscoll
and Mesta 2005, in prep.). Both of these dead adults are likely the
result of aggressive interactions with other bald eagles. The two
nestlings found dead were located within the crop of one of the dead
adult eagles. In Arizona, intruding eagles have killed nestlings and
fought with breeding eagles (Hunt et al. 1992, p. A146), and a breeding
eagle killed and ate its own nestling while still in the nest (Beatty
et al. 1995, p. 21). While the existence of these intruding eagles
identifies the presence of an important ``floating'' population, these
aggressive interactions may be a result of all serviceable breeding
areas being occupied, therefore necessitating ``stealing'' of a
territory (Hunt et al. 1992, p. A146). As a result, with only a few
territories known to be occupied by bald eagles in mainland Sonora,
these incidents could be an indication that additional suitable
territories are not available. However, due to the difficulty of
surveying and monitoring bald eagle nest sites in Sonora, we are not
certain that this type of conclusion can be supported at this time.
The Sonoran Desert Area population of the bald eagle in Arizona had
a mean estimated productivity rate of 0.80 between 1987 and 2003. Four
other populations documented by Allison et al. (2008, p. 31) had
estimates of productivity equal to or lower than that reported here,
while the remainder of the populations had higher rates. Exact
comparisons of productivity reported between studies are difficult, as
different methods were used to measure productivity, and these studies
occurred over different time periods. Studies in Arizona were more
intensive and, therefore, more likely to document mortality of
nestlings and fledglings beyond 8 weeks of age. This resulted in lower
productivity and nest success
[[Page 25822]]
estimates than would be obtained under a conventional protocol (Allison
et al. 2008, pp. 31-32).
In general, bald eagles in the Sonoran Desert Area of Arizona had
lower fledgling success than bald eagles elsewhere, but this has not
resulted in depressed productivity compared to other regions. The
occupancy rate of known breeding areas in Arizona was about 90 percent,
which is the same as that reported for Florida (Millsap et al. 2004, p.
1023). These high occupancy rates may indicate that the populations are
large enough to saturate available breeding areas (Stalmaster 1987, p.
141). If this is the case, further growth of the breeding population
would be limited by the lack of available nesting and foraging habitat.
However, as mentioned above in the Factor A discussion, the known
number of breeding areas within the Sonoran Desert Area has increased
from a low of three in 1971 to a high of 52 in 2009, and the population
has expanded into areas not previously occupied. This may indicate that
the population has not yet reached the point of saturation. Allison et
al. (2008, p. 32) noted that mechanisms such as habitat saturation,
density dependence, or continuing external threats to productivity
cannot be assumed at this point, and that low productivity levels by
themselves should not be used to interpret the status of the species in
Arizona. By themselves, productivity estimates are difficult to
interpret, because low productivity in a population may indicate a
population decline or, conversely, a recovered population.
Declining Prey Base
Appropriate prey resources are essential for the presence and
distribution of bald eagle breeding areas, and similarly for the
success of breeding attempts. Stalmaster (1987, p. 131) found that
foraging areas are the most essential components of the habitat used by
bald eagles, and they must provide an adequate amount of food in a
fairly consistent fashion. He further noted that food may be abundant
and nutritious, but if prey species are not accessible, they have no
value to an eagle. Stalmaster (1987, pp. 170-171) noted that food must
show a high level of continuity in its distribution, both in time and
space, to have the maximum benefit. Eagles are able to fast for long
periods; however, disruptions in prey abundance may cause excessive
nestling mortality, increase susceptibility to disease, or reduce the
general health of the bird.
Bald eagles rely on aquatic ecosystems as a source of a continuous
and accessible supply of fish for survival and reproduction (Stalmaster
1987, pp. 159, 170-171). Dams can affect both the habitat and prey base
of bald eagles by altering the flows of water and sediment in a stream
(Service 2002, p. I8). River damming, regulation, and diversion can
interrupt, reduce, or prevent the availability of fish to bald eagles.
Conversely, dams can provide an additional source of food for bald
eagles from fish that are killed in turbines, float downstream, and are
scavenged (Stalmaster 1987, pp. 131, 159). As mentioned above under
Factor A, reservoirs provide additional habitat diversity, especially
in a desert ecosystem, and may create a more stable food source for
bald eagles during the winter months due to congregations of waterfowl.
The creation of reservoirs usually coincides with the introduction of
exotic species of fish, some of which (e.g., catfish, bass, carp) can
deplete native fishes. However, these exotic species make up a large
portion of bald eagle diets in the Sonoran Desert Area, both in Arizona
and Sonora (Hunt et al. 1992, pp. A25-A26; Hunt et al. 2002, pp. 249-
251).
Native fishes have been declining rapidly across the desert
Southwest over the last century, and the desert aquatic environments in
which they have evolved have been altered by various chemical,
physical, and biological impacts. Within Arizona, populations of native
fishes have been reduced by dam construction, altered flow regimes,
loss of surface water, riparian vegetation degradation, and the
introduction of various nonnative species. Introduction of nonnative
fishes has had detrimental effects on native fishes through
competition, hybridization, alteration of habitat, disease transfer,
and predation (Bonar et al. 2004, p. 3; Minckley and Deacon 1991, pp.
15-17). As a result of competition and predation, nonnative fish have
replaced native fish in many central Arizona rivers (Rinne and Minckley
1991, p. 40), and competition with nonnative fishes is now the most
consequential factor preventing conservation and recovery of native
fishes in the Southwest (Meffe 1985, pp. 184-185; Minckley and Deacon
1991, pp. 15-17; Marsh and Pacey 2005, p. 62).
Unlike bald eagles that rely primarily on dead and dying fish
collected from the surface of lakes, bald eagles in the Sonoran Desert
Area that forage primarily in free-flowing streams (and regulated
stretches) rely upon capturing live fish (Hunt et al. 1992, p. A55).
Hunt et al. (1992, p. A70) cited fish diversity as a crucial feature of
suitable bald eagle breeding locations and native Sonoran and desert
suckers as an important prey item in riverine systems. Other important
fish species included exotic carp and channel catfish (Hunt et al.
1992, A26).
Various fish species become available to bald eagles as prey in
different ways and at different times. Live fish become vulnerable to
attack when they enter shallow water or swim near the surface. Within
the Sonoran Desert Area, the most vulnerable species in shallow water
are the bottom-feeders (e.g., Sonora sucker, desert sucker, carp,
channel catfish, flathead catfish) because of their downward visual
orientation (Hunt et al. 1992, p. A44). Species that spawn in shallow
water such as carp and suckers are especially vulnerable. Of the 134
depth measurements at strike points where Sonoran Desert Area bald
eagles captured fish, 70 (52 percent) were in water 20 cm (7.9 in) or
less in depth, and 92 percent were in water less than 100 cm (39.4 in)
deep (Hunt et al. 1992, p. A55).
Bald eagles in the Sonoran Desert Area are able to successfully
exploit a wide range of prey including nonnative fish, but there is a
specific sequence in the timing of prey availability such that one
species rarely dominates the diet of an eagle pair throughout an entire
breeding season. Pulses of increased prey availability occur throughout
the breeding season. This diversity of their foraging suggests that
threshold levels of prey, as well as habitat variation, may be
requisite to nest site selection and nestling success (Hunt et al.
1992, p. A70).
Within the sequencing of increased prey availability to bald eagles
nesting in riparian environments within the Sonoran Desert Area, native
Sonoran and desert suckers seem to be important, not only for how they
become available but also for when they become available. Suckers often
spawn in riffles, the shallowest of the riverine habitats, and may be
consistently exposed to attack at this stage of their life cycle
(Minckley 1973, pp. 162, 169; Hunt et al. 1992, p. A57). Water
temperature is the catalyst for fish spawning and, therefore, also
causes differences in timing of fish availability within breeding
areas. For example, the fact that suckers spawn early and carp (and
catfish) spawn later in the eagles' breeding season may be of
considerable advantage to nesting pairs of eagles. When both species
are common, the result may be a prolonged availability of food for
eagles (Hunt et al. 1992, p. A70). Suckers are the first of essential
species to become most available to eagles while they are incubating
eggs or
[[Page 25823]]
feeding small young. The movement of carp into shallow water to forage
generally occurs seasonally after suckers have finished spawning (Hunt
et al. 1992, p. A70). Because an eagle's foraging time is reduced due
to the necessity of incubation or the care of newly hatched nestlings
unable to regulate their own body temperature, the sucker's place in
the sequencing of available prey may be of added importance for
successful reproduction for eagles relying on free-flowing and
regulated streams. Additionally, there are no other fish species used
by bald eagles within the Sonoran Desert Area along rivers that have
the same spawning schedule and accessibility to nesting eagles.
In the mid-1990s, an increase in nesting failure of previously
successful bald eagle breeding areas along the free-flowing upper Salt
River led to an examination of fish species diversity along this
portion of the river. The introduction of predatory flathead catfish in
the late 1970s nearly extirpated native fish populations, including
previously abundant suckers. Flathead catfish, while available as bald
eagle prey when smaller, grow to large sizes (up to 50 pounds), making
them too large to be of use as prey. Large flathead catfish have also
been observed preying upon smaller flathead catfish. The situation on
the Salt River allowed observation of how the absence (or significant
reduction) of a previously abundant prey species disrupted the temporal
sequencing of prey availability and may have affected bald eagle
productivity. The productivity of breeding areas along the upper Salt
River decreased from the 1980s to the 1990s, and an increase in
predatory catfish may have contributed to this decline (Driscoll et al.
2006, p. 19).
A similar trend in productivity (e.g. decline from the 1980s to the
1990s) was observed in the entire Sonoran Desert Area population of
bald eagles during this time period, and it is possible that other
factors may have contributed to the decline observed in the upper Salt
River breeding areas. However, low productivity continues to occur in
the upper Salt River breeding areas, while productivity has increased
in other portions of the Sonoran Desert Area. Overall, productivity of
bald eagles within the Sonoran Desert Area, even with the reductions
observed in the upper Salt River, is consistent with that observed in
other areas of the species' range (Driscoll et al. 2006, p. 5). It is
possible that changes in fish populations (among other manmade impacts
to streams) may be affecting the likelihood of expansion of bald eagles
into currently unoccupied sections of other Sonoran Desert Area rivers.
On the free-flowing middle Verde River between Camp Verde and
Horseshoe Lake, two previously productive bald eagle breeding areas are
now observed to fail with consistency. For the first 39 years of their
existence up to 1999, they were successful a combined 26 times. Since
2000, in a combined 18 nest years, they were successful only once
(Driscoll et al. 2006, pp. 35-36, 48-50; AGFD 2007, pp. 33-34; AGFD
2008a, pp. 38-39). However, during the same time period, two other
breeding areas located on this section of the Verde River have been
successful a combined 14 times. Investigations into the distribution,
abundance, and proportion of native and nonnative fish species along
this length of the Verde River found native species the least abundant
and nonnative the most abundant in this section of the Verde River. The
conclusion for this distribution was that the low densities of native
fish may be caused by continual predation since the early 1900s (Bonar
et al. 2004, p. 3). Hunt et al. (1992, p. A46) also concluded that the
rarity of suckers in river sections upstream of the reservoirs is also
partially a result of sucker populations being overwhelmed by large
numbers of carp and catfish from the reservoirs. Other predatory exotic
fish, like smallmouth bass, may also contribute to the predation of
native fish in this section of the Verde River.
It is informative to observe where bald eagles have established
breeding areas and whether there is any relationship between those
locations and the locations where impacts to prey resources may have
already occurred prior to the modern day monitoring of bald eagle
territories. For example, as discussed above, the majority of bald
eagle productivity in the Sonoran Desert Area, exclusive of Sonora, is
tied to breeding areas along the Salt and Verde Rivers. The Gila River
and Lower Colorado River within the Sonoran Desert Area both provide
miles of river with similar attributes to the Salt and Verde Rivers
(e.g., presence of large-bodied fishes, cliffs and large trees for
nesting, perennial flow, and existing bald eagle breeding areas). Five
productive bald eagle breeding areas exist along or adjacent to these
waterways. However, unlike the Salt and Verde Rivers, where eagles
exist upstream and downstream of reservoirs, no bald eagle breeding
areas are solely associated with the regulated mainstem Colorado River
or the free-flowing Gila River above San Carlos Lake within the Sonoran
Desert Area. All of their foraging areas are primarily associated with
reservoirs (San Carlos Lake, Talkalai Lake, and Copper Basin/Gene Wash
Reservoir). While two breeding areas were established along the
regulated Gila River below Coolidge Dam at San Carlos Lake since the
mid- to late-1990s, these pairs have never been successful (and only
laid eggs five times) in their 23 combined nest years. These observed
patterns and lack of success along the free-flowing and regulated
sections of the Gila and Colorado Rivers within the Sonoran Desert Area
are indicative that conditions are not conducive to successful nesting,
and, based upon similar patterns observed along the upper Salt and
Verde Rivers, lack of prey diversity may be a contributing factor.
Similar to bald eagles in the Sonoran Desert Area of Arizona, fish
species eaten by nesting eagles in Mexico are a combination of
nonnative and native fishes. Identified fish found in prey remains
collected from nests were nonnative channel catfish, carpsucker
(Carpiodes carpio), carp, tilapia (Tilapia sp.), largemouth bass, and
native Yaqui catfish (Ictalurus pricei) and Yaqui sucker (Catostomus
bernardini) (Driscoll and Mesta 2005, in prep.). Nonnative species,
such as bullfrogs and sport and bait fish, have been introduced
throughout Mexico, and continue to disperse naturally, broadening their
distributions (Conant 1974, pp. 487-489; Miller et al. 2005, pp. 60-61;
Luja and Rodriguez-Estrella 2008, pp. 17-22). The damming and
regulation of Mexican rivers and the addition of nonnative fishes are
expected, over time, to continue to provide conditions favorable to
nonnative fish and declines in native fish (Unmack and Fagan 2004, p.
233).
Minckley and Miller (in Miller et al. 2005, p. 61) noted that
Mexico's critical need for domestic, irrigation, and industrial water
supplies and electrical power are being met through the impoundment of
both major and minor rivers. They conclude that dams have remarkably
harmful effects on riverine systems and native fishes, and that they
result in the establishment of nonnative fishes, which is considered
the single greatest challenge to survival of native fish species.
Unmack and Fagan (2004, p. 233) noted that the current status of
nonnative fishes in the Yaqui Basin is remarkably similar to what was
evident from the Gila Basin in Arizona and that, without strong action,
the native fish of the Yaqui Basin will become increasingly imperiled
over the next several years. While nesting bald eagles can take
advantage of the variety of
[[Page 25824]]
fishes along rivers, including introduced catfish and carp (Hunt et al.
1992, pp. Aii, Aiii), it is unclear to what extent nonnative fishes may
be affecting the reproductive success of bald eagles in Mexico.
The ``Conservation Assessment and Strategy for the Bald Eagle in
Arizona'' identifies the need to concentrate efforts on restoring
native fish populations and fish diversity to stabilize bald eagle
productivity and enhanced survival (Driscoll et al. 2006, pp. 51-53).
However, efforts to accomplish increased fish diversity along regulated
and free-flowing streams within the Sonoran Desert Area are difficult,
complex, and require considerable funding, time, and public support.
Even then, there is uncertainty over their success. For example,
stocking of Colorado pikeminnow and razorback suckers has occurred
within the Sonoran Desert Area on the Verde, Salt, Gila, and lower
Colorado Rivers with little to no success. The Service is not aware of
any management actions designed to improve the diversity of native
Sonoran or desert suckers along the mainstem of these rivers within the
Sonoran Desert Area, whereas sportfish stocking of nonnative species
such as catfish and largemouth bass continue to be widespread in
Arizona.
There is little evidence to suggest that without active management
the balance of native and nonnative fish will be maintained or
improved. At present, nonnative fish stocking continues with stocking
schedules posted online, including schedules for stocking of the Salt
and Verde Rivers. Each year, the AGFD stocks more than three million
fish--including rainbow, Apache, brook, and cutthroat trout; largemouth
bass; and channel catfish--in approximately 160 of Arizona's lakes,
rivers, and streams (AGFD 2009b, p. 1). The stocking program is
supported with Federal funds through the Federal Aid in Sport Fish
Restoration Program, along with State funds from the sale of licenses
and trout stamps. The Service is undergoing consultation in
coordination with AGFD on the proposed stocking program for the next 10
years. The consultation will include an assessment of anticipated
impacts of stocking of nonnative fish and their impacts on prey
diversity for bald eagles into the future.
Based upon continued sportfish stocking, we anticipate continued
increases in nonnative fish and reduced abundance and distribution of
native fish on central Arizona rivers and reservoirs within the Sonoran
Desert Area. Regarding recovery of native fishes in the southwestern
United States, Clarkson et al. (2005, pp. 20, 23) noted, ``no amount of
habitat restoration can successfully advance biological recovery unless
preceded or accompanied by elimination of nonnatives.'' They further
noted that nonnative species already occupy reservoirs and the few
natural lakes in the Southwest, and that it is impractical to eliminate
these fishes from lake habitats. They noted that medium and small warm-
water streams and stream systems may be suitable for recovery of native
fishes. However, for the most part, these are not the streams that
support bald eagles. For those pairs relying on prey from regulated or
free-flowing streams, the loss of fish diversity may be causing
negative effects to reproduction at the localized level.
Despite this apparently continuing decrease in fish diversity, the
best available information suggests that the scope and intensity of the
effect this decrease in diversity is having or will have on the Sonoran
Desert Area population of the bald eagle does not appear to be
sufficient to result in population-level effects. While previously
successful breeding areas located on the middle Verde River and upper
Salt River have declined in productivity in recent years, these
breeding areas continue to be occupied, and young are occasionally
produced; new breeding areas and other non-riverine sites are producing
eagles; and overall productivity rates within the Sonoran Desert Area
are within the range of rates observed in other bald eagle populations.
Therefore, after a review of the best available commercial and
scientific information, we conclude that a declining prey base does not
constitute a significant threat to the Sonoran Desert Area population
of the bald eagle at the population level.
Contaminants, Pollutants, and Eggshell Thinning
As a barometer of environmental health at the top of the food
chain, bald eagles are susceptible to impacts from contaminants that
can accumulate in the bodies of fish (Newton 1979, pp. 230-231) and
pollutants that can affect prey (Newton 197, p. 259). Water pollution
was identified in a list of threats to aquatic biota in Mexico by
Miller et al. (2005, pp. 60-61), and, clearly, contaminants such as
organochlorides (e.g., Dichlorodiphenyldichloroethylene (DDE),
Dichlorodiphenyltrichloroethane (DDT)) and heavy metals (e.g., mercury,
lead) continue to be threats to bald eagles. These contaminants can
typically be associated with agriculture, urbanization, mining, and
other resource uses (Newton 1979, pp. 230, 254-255). Similarly,
pollution that kills or reduces fish populations directly affects the
abundance, diversity, or availability of food needed for bald eagle
reproduction.
The AGFD and the Service analyzed 27 addled bald eagle eggs in
Arizona from 1994 to 2004 that showed mercury levels ranging from 0.55
to 8.02 parts per million (ppm). Of these eggs, 10 were classified as
toxic (exceeding 2.0 ppm), 11 had elevated levels (1.5 to 2.0 ppm), and
four had lesser concentrations (1.0 to 1.5 ppm). The 10 eggs classified
as toxic came from breeding areas located on the Salt, Verde, and Gila
Rivers and Tonto Creek (Driscoll et al. 2006, p. 21). While eggs tested
for mercury were addled and did not produce young, successful
production of young has occurred at all of these breeding areas
following the year or years in which mercury was detected (viable eggs
are not collected and tested for mercury). For example, a breeding area
located on Tonto Creek had the highest ever recorded mercury level for
eggs from Arizona in 1995, but the pair successfully produced young in
1996 through 2001, 2007, and 2008. Assuming mercury was the cause of
nest failure, these data indicate that high levels of mercury in eggs
at a given nest site may cause nest failure for one season, but future
reproduction may not be affected.
Lead poisoning is an additional stressor for breeding areas within
the Sonoran Desert Area. Lead poisoning in bald eagles has been linked
to ingestion of lead gunshot, consumption of lead sinkers, and
secondary consumption of lead-contaminated prey. Research indicates
that toxic liver lead levels for bald eagles rangewide is somewhere
between 6.0 and 10.0 ppm (Pattee et al. 1981, pp. 808-809; Driscoll et
al. 2006, p. 20). From 1998 to 2004, 22 bald eagles (or 39 percent of
all documented mortalities rangewide) had liver lead levels averaging
32.9 ppm and ranging from 0 to 9 times the toxic threshold. Only one of
the eagles confirmed to have lead poisoning was fledged from a nest in
Arizona. Because bald eagles travel large distances, the ingestion of
lead could occur in any area along their migration, making it difficult
to determine the source of the poisoning (Driscoll et al. 2006, pp. 20-
21).
Organochlorides continue to be detected in bald eagle eggs within
the Sonoran Desert Area, with a recent measurement of DDE at 4.23 ppm
wet weight in one egg from a breeding area on the lower Verde River in
2002. A reduction in productivity is known to occur when DDE values in
bald eagle
[[Page 25825]]
eggs are between 3 and 5 ppm (wet weight) (Wiemeyer et al. 1984, p.
541). This level has been reached in eggs collected from three breeding
areas along the Verde River and one located on Tonto Creek. The most
complete DDE data set over time is from a breeding area located on the
upper Verde River, where DDE concentrations declined from 3.2 ppm in
1994 to 0.91 ppm in 2001. Following DDE levels of 3.20 ppm (wet
weight), this breeding area produced young in 1996 through 2003, and
2005 through 2007. At another breeding area located on the upper Salt
River, young have been produced since DDE levels of 4.17 ppm (wet
weight) were found in 2001. At one breeding area located on the lower
Verde River, DDE levels of 7.00 ppm (wet weight) were detected from an
egg collected in 1997, but the breeding area produced young in 1998,
1999, and 2001 through 2008. Similarly, another breeding area in the
same area, with DDE levels of 4.23 ppm in 2002, produced young in 2004
and 2006 through 2008 (Driscoll et al. 2006, p. 22).
DDT is known to cause eggshell thinning. For bald eagles, eggshell
thinning greater than 10 percent can cause difficulties in reproduction
(Wiemeyer et al. 1984, p. 543). The AGFD found five separate occasions
on which eggshell thinning in Arizona equaled or exceeded 10 percent
between 1993 and 2004 (Driscoll et al. 2006, p. 23). However, the AGFD
concluded that other factors may have a greater influence on
productivity than DDT, but that egg collection and eggshell
measurements will continue to ensure that the effects of DDT and other
organochlorides are monitored. The Service agrees with this conclusion,
and believes that eggshell thinning warrants further study and
monitoring; however, at this time, the Service is not aware of any data
to indicate eggshell thinning at the levels cited is resulting in lost
reproduction.
In mainland Sonora, bald eagle eggs collected in the late 1980s
were analyzed for metabolized DDE. Organochloride levels were well
below concentrations that reduce productivity, and eggshell thickness
was near pre-DDT levels (Driscoll and Mesta 2005, in prep.). In
addition to pesticides, other contaminants may be in use near bald
eagle breeding areas in mainland Sonora. Gold mines are located
sporadically along the Rio Yaqui. Many of the mines are old and
inoperable, but some have been reopened, with strychnine used to leach
gold from the ore. These mines are often adjacent to the rivers in
arroyos where runoff could lead to stream contamination (Driscoll and
Mesta 2005, in prep.). Based upon increasing human populations and
proximity of agriculture and mining to rivers where eagles nest or
could nest in the future, the current and future impacts of
contaminants and pollution on bald eagle health and reproduction in
Mexico are unknown.
In addition to monitoring bald eagle eggs, the Service has been
evaluating the effects of mercury, organochlorides, and other
pesticides for many years. The AGFD and the Service have developed a
protocol for identifying, documenting, and processing all bald eagle
carcasses found in Arizona, which will allow for the continued
monitoring of mortality factors, including lead poisoning and other
contaminants.
Based on the above information, contaminants, pollutants, and
eggshell thinning have likely resulted in historical and continued
impacts to the reproductive success of bald eagles in the Sonoran
Desert Area. Specifically, organochlorides and mercury have been
detected within the Sonoran Desert Area at levels that are known to
affect productivity, but all of the affected breeding areas have
continued to produce young. Many of these are among the most productive
breeding areas located within the Sonoran Desert Area. Bald eagles in
the Sonoran Desert Area are potentially exposed to contaminants and
pollutants throughout their range. However, the impact from these
threats has been of low magnitude, and does not persist for long
periods of time. The best scientific information suggests that
contaminants, pollutants, and eggshell thinning do not constitute a
significant threat to the Sonoran Desert Area population of the bald
eagle at the population level.
Fishing Line and Tackle
Fishing line and tackle have been found in bald eagle nests, and
have entangled bald eagles within the Sonoran Desert Area of Arizona.
In response to this problem, the AGFD developed a monofilament recovery
program in 2002. Although this program is voluntary, it has helped to
educate anglers and reduce the amount of improperly disposed
monofilament. Fishing line entanglement is most frequent on the lower
Verde River (19 percent of occurrences), the upper Salt River (17
percent of occurrences), and Alamo Lake (14 percent of occurrences)
(Driscoll et al. 2006, p. 18). Bald eagles encounter fishing line
primarily by catching dead or dying fish with fishing line or tackle
still attached, and they may also collect it for use as nest material
(Hunt et al. 1992, p. A135; AGFD 1998, p. 5). For probable causes of
mortality in bald eagles in Arizona between 1987 and 2005, monofilament
was the cause of one adult mortality and two nesting mortalities
(Driscoll et al. 2006, pp. 17-18). It was ranked as the fifteenth most
common cause of mortality, and responsible for 3 out of 281 deaths, or
approximately 1.1 percent (Driscoll et al. 2006, p. 25). Although
monofilament has been shown to affect bald eagles within the Sonoran
Desert Area of Arizona, it represents a minor threat, because the
magnitude of the effects to the bald eagle is small (i.e., representing
1.1 percent of known mortality). We attribute the limited effect that
monofilament is having on bald eagles within the Sonoran Desert Area of
Arizona to the active management of the ABENWP, which we anticipate
will continue. Additionally, wildlife personnel entering nests to
conduct annual banding are instrumental in removing large quantities of
monofilament (Driscoll et al. 2006, p. 11).
Climate Change
Our analyses under the Endangered Species Act include consideration
of ongoing and projected changes in climate. The terms ``climate'' and
``climate change'' are defined by the Intergovernmental Panel on
Climate Change (IPCC). ``Climate'' refers to the mean and variability
of different types of weather conditions over time, with 30 years being
a typical period for such measurements, although shorter or longer
periods also may be used (IPCC 2007, p. 78). The term ``climate
change'' thus refers to a change in the mean or variability of one or
more measures of climate (e.g., temperature or precipitation) that
persists for an extended period, typically decades or longer, whether
the change is due to natural variability, human activity, or both (IPCC
2007, p. 78). Various types of changes in climate can have direct or
indirect effects on species. These effects may be positive, neutral, or
negative, and they may change over time, depending on the species and
other relevant considerations, such as the effects of interactions of
climate with other variables (e.g., habitat fragmentation) (IPCC 2007,
pp. 8-14, 18-19). In our analyses, we use our expert judgment to weigh
relevant information, including uncertainty, in our consideration of
various aspects of climate change.
Seager et al. (2007, pp. 1181-1184) analyzed 19 computer models
that used many different variables to estimate the future climatology
of the Southwestern United States and northern Mexico in
[[Page 25826]]
response to predictions of climatic patterns. All but one of the 19
models predicted a drying trend within the Southwest; one predicted a
trend toward a wetter climate. Researchers created 49 projections using
19 models, and all but 3 predicted a shift to increasing aridity
(dryness) in the Southwest as early as 2021-2040. Recently published
projections of potential reductions in natural flow on the Colorado
River Basin by the mid-21st century range from approximately 43 percent
by Hoerling and Eischeid (2007, p. 35) to approximately six percent by
Christensen and Lettenmaier (2006, pp. 3727-3729). The U.S. Climate
Change Science Program (CCSP), in a recent report on climate change,
concluded for the Southwest that ``subtropical aridity is likely to
intensify and persist due to future greenhouse warming'' (CCSP 2008, p.
2).
The anticipated effects from climate change in the Southwest can be
separated into three general predictions. First, climate change is
expected to shorten periods of snowpack accumulation, as well as lessen
snowpack levels. With gradually increasing temperatures and reduced
snowpack (due to higher spring temperatures and reduced winter-spring
precipitation), annual runoff will be reduced (Smith et al. 2003, p.
226; Garfin 2005, p. 42), consequently reducing groundwater recharge.
Second, snowmelt is expected to occur earlier in the calendar year,
because increased minimum winter and spring temperatures could melt
snowpacks sooner, causing peak water flows to occur much sooner than
the historical spring and summer peak flows (Smith et al. 2003, p. 226;
Stewart et al. 2004, pp. 217-218, 224, 230; Garfin 2005, p. 41) and
reducing flows later in the season. Third, the hydrologic cycle is
expected to become more dynamic on average, with climate models
predicting increases in the variability and intensity of rainfall
events. This will modify disturbance regimes by changing the magnitude
and frequency of floods.
Climate change will likely cause an increase in river temperatures
in drier climates. This will in turn result in periods of prolonged low
flows and stream drying and an increased demand for water storage and
conveyance systems (Rahel and Olden 2008, pp. 521-522, 526). Warmer
water temperatures across temperate regions are predicted to expand the
distribution of existing aquatic nonnative species by providing more
suitable habitat. These species are often tropical in origin and
adaptable to warmer water temperatures. This conclusion is based upon
studies that compared the thermal tolerances of 57 fish species with
predictions made from climate models (Mohseni et al. 2003, p. 389).
We are uncertain about the magnitude of the threat posed by climate
change, because we do not currently understand all potential impacts of
climate change on bald eagles or the human population. However, based
on the best information available, we conclude that climate change is
not a significant threat, because the extent to which the bald eagle
will respond to climate change is unclear. We have to date not detected
climate change-related impacts to the Sonoran Desert Area population of
the bald eagle; moreover, bald eagles in the Sonoran Desert Area, and
elsewhere within their range, have been shown to be highly adaptable
(e.g., feed on a variety of prey, nest in many types of structures,
breed in a variety of habitats throughout their range). This life-
history trait contributes to the ability of the Sonoran Desert Area
population of the bald eagle to continue to exist even under some of
the possible effects from climate change.
Human Disturbance
Small planes and helicopters are the most common human activities
in bald eagle breeding areas in Arizona (Driscoll et al. 2006, p. 18).
From 1998 to 2005, low-flying aircraft were responsible for 37.1
percent (n = 23,905) of all human activities and 25.3 percent (n =
1,273) of the significant responses (e.g., restless, flushed, and left
the area) by a breeding pair. For the period from 1998 to 2005,
significant responses to low-flying aircraft ranged from 10.6 percent
to 44.1 percent of all significant responses by a breeding pair. The
potential impacts from an eagle responding to low-flying aircraft
include the inadvertent cracking of an egg as a result of flushing an
incubating adult or premature fledging. Driscoll et al. (2006, p. 18)
concluded that, while no direct link of a nest failure to low-flying
private aircraft has occurred, this activity will increase with the
demand for tourism flights, especially in remote breeding areas. In
addition to private aircraft, many Sonoran Desert Area breeding areas
are located near military training routes used by the Department of
Defense. The Salt River Pima-Maricopa Indian Community is also
concerned with military helicopter flights disturbing nesting bald
eagles. While high-speed aircraft may not disturb bald eagles when an
appropriate buffer distance is maintained, noise disturbance and sonic
booms can cause a reaction (Ellis et al. 1991, p. 53; Grubb et al.
1997, pp. 216-217).
Driscoll et al. (1999, p. 220) noted that, of 24 eggs (in 13
clutches) for which we knew the cause of mortality, 11 involved human
disturbance (over a 7-year period). The ABENWP has recorded a three-
fold increase in the average number of human activities that occur
within 1 km (0.6 miles) of all monitored bald eagle breeding areas in
the last 16 years (Driscoll et al. 2006, p. 16). Anticipated human
population growth, as described above, will lead to an increased demand
in water-based recreation in areas currently supporting breeding areas.
Monitoring and seasonal closures by the ABENWP around some breeding
areas help to minimize these impacts. However, not all breeding areas
are covered by these measures. In addition, disturbance from
recreational activities may affect the ability of bald eagles to
forage, as adults need foraging areas without constant human
disturbance in order to capture prey.
Recreation outside of nesting areas may limit foraging
opportunities and affect adult, nestling, and juvenile survival, as
well as egg production (Driscoll et al. 2006, p. 17). It is anticipated
that increasing recreational pressures will continue to occur on the
lower Gila River, San Carlos River, Salt River, Verde River, Tonto
Creek, Alamo Lake, and Lake Pleasant. The ``Conservation Assessment and
Strategy for Bald eagles in Arizona'' identified `human activity' as a
management challenge for 36 of 45 breeding areas (or 80 percent)
located within the Sonoran Desert Area at that time (Driscoll et al.
2006, pp. 51-53). However, human activity within close proximity to
nests does not in itself necessarily result in negative effects to the
productivity of a bald eagle breeding area.
As an example of the ability of the bald eagle to adapt to human
activity, a 5-year study in Florida of rural (< 5 percent intensive
human use within 1,500 meters) and suburban (> 50 percent intensive
human use within 1,500 meters) bald eagle nests did not detect a
significant difference between the two groups in occupancy rates or
productivity. These results suggest that bald eagles in their study
area may have adapted to, or at least tolerated, increasing human
populations and disturbance (Millsap et al 2004, p. 1023). However, the
authors caution that their results merely point out that some eagles
can successfully coexist with intensive human activity, but this should
not be interpreted to mean that all eagles can. Within the Sonoran
Desert Area of Arizona, the bald eagle breeding areas located in
closest proximity to the Phoenix metropolitan area on the lower Verde
and Salt Rivers
[[Page 25827]]
are also some of the most productive (Allison et al. 2008, pp. 17-18).
Therefore, we conclude that human disturbance is not a significant
threat to the Sonoran Desert bald eagle population.
Summary of Factor E
We evaluated a number of other factors that could affect the
continued existence of the Sonoran Desert Area population of the bald
eagle: Demographic factors; declining prey base; contaminants,
pollutants, and eggshell thinning; fishing line and tackle; climate
change; and human disturbance. After analyzing the best available
information regarding these potential threats and the data regarding
how eagles have responded to these factors, we concluded that none of
them poses a significant threat to the Sonoran Desert Area bald eagle
at a population level.
Three models have been completed that analyzed the future risk of
extinction to the Sonoran Desert Area population of the bald eagle
taking into consideration a number of demographic variables. The
results of the model that best matched observed population
trajectories--because it used an adjusted survival rate for juvenile
and subadult eagles--suggest that the Sonoran Desert Area population of
the bald eagle is not at a risk of extinction in the future. In
addition, observed mortality rates, productivity, and survival rates
for bald eagles within the Sonoran Desert Area are all within the range
of observed values for other bald eagle populations throughout the
United States.
The availability of an adequate and accessible supply of prey is
essential to the success of breeding bald eagles in the Sonoran Desert
Area. The presence of reservoirs, dams, or regulated rivers does not
appear to have had a negative impact on bald eagle reproduction, and
may be providing a more stable food source for bald eagles than would
otherwise be available in the Sonoran Desert ecosystem. Native fish
populations have been declining in the Sonoran Desert Area of Arizona
due to the introduction of nonnative fish and alterations to their
habitat. Declining populations of native fish along portions of the
Salt and Verde Rivers may be a factor contributing to a localized
reduction in productivity for pairs of bald eagles nesting in these
areas. However, bald eagles are capable of exploiting a wide range of
prey species, and nonnative fishes make up a large portion of their
diet within the Sonoran Desert Area.
Several breeding areas within the Sonoran Desert Area have
experienced high levels of mercury or organochlorides. The productivity
of pairs at those breeding areas indicates that, while nest failure may
occur when those levels are detected, young continue to be produced in
subsequent years. Several bald eagles have died of lead poisoning while
in Arizona, but only one of these eagles is known to have fledged from
a nest in Arizona. The long distance traveled by migrating eagles could
mean that the ingestion of lead is occurring outside of Arizona. The
protocol developed by AGFD and the Service for identifying,
documenting, and processing bald eagle carcasses will allow for the
continued monitoring of mortality factors, including lead poisoning and
other contaminants. Based on the best available information, the
Service concludes that the effects of contaminants should continue to
be monitored, but they are currently not a significant threat to the
Sonoran Desert Area population of the bald eagle.
Fishing line and tackle have been found in bald eagle nests, and
have entangled bald eagles within the Sonoran Desert Area of Arizona.
However, fishing line is ranked as the fifteenth most common cause of
mortality, responsible for only 1.1 percent of known mortalities. Our
review of the best available information indicates that fishing line is
not a significant threat to the Sonoran Desert Area population of the
bald eagle.
Bald eagles in the Sonoran Desert Area depend on aquatic ecosystems
for survival, and those aquatic ecosystems are predicted to be at risk
due to drying under climate change scenarios. Potential drought
associated with changing climatic patterns may adversely affect
streams, rivers, and reservoirs--not only reducing water
characteristics and availability, but also altering food availability.
These changes may in turn exacerbate existing threats to bald eagles
and their habitat in the Sonoran Desert Area. However, to date no
impacts to bald eagles from climate change have been recorded, and it
is unclear whether the bald eagle will adapt to these changes or
respond at a population level.
Human disturbance to nesting and foraging bald eagles from small
planes, helicopters, military aircraft, and recreational activities has
occurred in the past, is occurring now, and will likely continue to
occur within the Sonoran Desert Area. The activities of the ABENWP and
seasonal closures of breeding areas have helped to mitigate this impact
at the local level, and will continue to be implemented into the
future. As stated above, there has not been any indication that human
disturbance has led to the failure of bald eagle breeding attempts, or
to population-level effects.
After reviewing the best available commercial and scientific
information, based on our analysis above, we conclude that demographic
factors; a declining prey base; contaminants, pollutants, and eggshell
thinning; fishing line and tackle; climate change; and human
disturbance are not significantly contributing to the risk of
extinction of the Sonoran Desert Area population of the bald eagle at
the population level.
Finding
In making this finding, as directed by the court, we used the
information contained in our 2010 administrative record which included
information provided by the petitioners, as well as other information
in our files, and otherwise available. The information we reviewed
included information submitted by the public and the Tribes, and
available published and unpublished scientific and commercial
information. Additionally, we had information from Federal, State, and
Tribal land managers, along with recognized experts in conservation and
bald eagle biology. This 12-month finding reflects and incorporates
information from our 2010 administrative record that we received from
the public and through consultation, literature research, and field
visits. Based on the rationale detailed above, we find that bald eagle
population in the Sonoran Desert Area is discrete from other bald eagle
populations, but is not significant to the bald eagle as a whole, and
therefore is not a valid DPS, pursuant to the DPS Policy (61 FR 4722).
Next, we reviewed our 2010 administrative record regarding the
past, present, and future threats faced by the Sonoran Desert Area
population of the bald eagle. This status review identified threats to
the Sonoran Desert Area population of the bald eagle under Factors A
and E. The primary threats to the Sonoran Desert Area population of the
bald eagle--the activities that the population has responded to most
significantly--are from the degradation and loss of riparian habitat
and the loss of surface flows from groundwater pumping and surface
water diversions (Factor A). In the Sonoran Desert Area, bald eagle
breeding areas are located in close proximity to a variety of aquatic
sites, including reservoirs, regulated river systems, and free-flowing
rivers and creeks. The essential components of these sites for bald
eagles are the
[[Page 25828]]
availability of trees for roosting, perching, hunting, and nesting, and
access to prey, primarily fish. The decline of riparian habitat stems
specifically from direct loss from development and indirect impacts
from the loss of surface flows.
With respect to each kind of threat, the best available information
has confirmed a response to the threat, such as a decrease in breeding
rates or survival rates. However, the potential for population-level
impacts to bald eagles throughout their range--including in the Sonoran
Desert Area--from the degradation or loss of riparian habitat and the
loss of surface flows from groundwater pumping and surface water
diversions has been reduced by the regulatory mechanisms in place
within the United States and locally, the strong ability of bald eagles
to adapt to changes in their environment, the widespread distribution
of bald eagles along rivers within the Sonoran Desert Area, and the
availability of reservoirs. Additional potential threats to the Sonoran
Desert Area population of the bald eagle include demographic factors;
declining prey base; contaminants, pollutants, and eggshell thinning;
fishing line and tackle; climate change; and human disturbance.
However, based on the best available information none of these poses a
significant threat at a population level.
We must also evaluate whether these combined potential threats
present a significant threat to the Sonoran Desert Area bald eagle
population. If these threats were acting, either independently or
cumulatively, in such a manner as to likely cause a significant risk of
extinction to the population, we would expect to see them expressed in
terms of the demographic factors that we reported in our analysis. In
fact, all of the rates (e.g., mortality, survival, productivity, and
occupancy) associated with the demographic factors for the Sonoran
Desert Area population of the bald eagle were within the range of
values observed in other populations of the bald eagle in the United
States. More importantly, simple counts of bald eagles breeding in
Arizona each year indicated that the breeding segment increased at an
average rate of 4.0 percent per year from 1987 to 2003 (Allison et al.
2008, p. 26). Therefore, although the threats described above vary in
their scope and intensity, the Service considers the overall threat to
the Sonoran Desert Area population of the bald eagle from these factors
to be low.
On the basis of the best scientific and commercial data available,
we find that listing the Sonoran Desert Area population of the bald
eagle as threatened or endangered is not warranted. We arrive at this
determination because, despite the presence of these same threats for
decades, the Sonoran Desert Area population of the bald eagle remains
stable or increasing. In our analysis, we have indicated that some of
the threats are likely to increase in the future. However, we do not
have any information to suggest that these are significant threats or
threats that could cause the Sonoran Desert Area population of the bald
eagle to be in danger of extinction, or likely to become so in the
foreseeable future.
We encourage interested parties to continue to gather data that
will assist with the conservation of the species. If you wish to
provide information regarding the bald eagle, you may submit your
information or materials to the Field Supervisor, Arizona Ecological
Services Office (see ADDRESSES section above). The Service continues to
strongly support the cooperative conservation of the Sonoran Desert
Area bald eagle.
References Cited
A complete list of all references cited herein is available at
http://www.regulations.gov at Docket No. FWS-R2-ES-2008-0059, upon
request, from the Southwest Regional Office of the U.S. Fish and
Wildlife Service (see ADDRESSES section above).
Author
The primary authors of this notice are the staff of the Southwest
Region of the U.S. Fish and Wildlife Service.
Authority
The authority for this section is section 4 of the Endangered
Species Act of 1973, as amended (16 U.S.C. 1531 et seq.).
Dated: April 17, 2012.
Daniel M. Ashe,
Director, Fish and Wildlife Service.
[FR Doc. 2012-10016 Filed 4-30-12; 8:45 am]
BILLING CODE 4310-55-P