[Federal Register: July 25, 2001 (Volume 66, Number 143)]
[Proposed Rules]               
[Page 38611-38626]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]



Fish and Wildlife Service

50 CFR Part 17

Endangered and Threatened Wildlife and Plants; 12-Month Finding 
for a Petition To List the Yellow-billed Cuckoo (Coccyzus americanus) 
in the Western Continental United States

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Notice of 12-month petition finding.


SUMMARY: We, the U.S. Fish and Wildlife Service (Service), announce a 
12-month finding for a petition to list the yellow-billed cuckoo 
(Coccyzus americanus) in the western continental United States under 
the Endangered Species Act of 1973, as amended (Act). We find that the 
petitioned action is warranted, but precluded by higher priority 
listing actions. We will develop a proposed rule to list this 
population pursuant to our Listing Priority Guidance. Upon publication 
of this notice of 12-month petition finding, this species will be added 
to our candidate species list.

DATES: The finding announced in this document was made on July 18, 
2001. Comments and information may be submitted until further notice.

ADDRESSES: You may submit data, information, comments, or questions 
concerning this finding to the Supervisor, U.S. Fish and Wildlife 
Service, Sacramento Fish and Wildlife Office, 2800 Cottage Way, Room 
2605, Sacramento, California 95825. You may inspect the petition, 
administrative finding, supporting information, and comments received, 
by appointment, during normal business hours at the above address.

FOR FURTHER INFORMATION CONTACT: Stephanie Brady, Fish and Wildlife 
Biologist, at the above address, by telephone at 916/414-6600, 
facsimile at 916/414-6613, or electronic mail at 



    Section 4(b)(3)(B) of the Endangered Species Act of 1973, as 
amended (Act) (16 U.S.C. 1531 et seq.), requires that, for any petition 
to revise the List of Threatened and Endangered Species containing 
substantial scientific and commercial information that listing may be 
warranted, we make a finding within 12 months of the date of the 
receipt of the petition on whether the petitioned actions is: (a) not 
warranted, (b) warranted, or (c) warranted but precluded from immediate 
proposal by other higher priority efforts to revise the List of 
Threatened and Endangered Species. Section 4(b)(3)(C) requires that 
petitions for which requested action is found to be warranted but 
precluded should be treated as though resubmitted on the date of such 
finding, i.e., requiring a subsequent finding to be made within 12 
months. Such 12-month findings are to be published promptly in the 
Federal Register.
    Section 4(b) of the Act states that we may make warranted but 
precluded findings only if we can demonstrate that: (1) An immediate 
proposed rule is precluded by other pending actions, and (2) 
expeditious progress is being made on other listing actions. Due to the 

[[Page 38612]]

amount of litigation over critical habitat, we are working on numerous 
court orders and settlement agreements. Complying with these orders and 
settlement agreements will consume nearly all or all of our listing 
budget for fiscal year 2001. Any funding we may have available for 
discretionary listing actions will likely be allocated for emergency 
listings only. However, we can continue to place species on the 
candidate species list, as that work activity is funded separately from 
our listing program.
    On February 9, 1998, we received a petition, dated February 2, 
1998, from Robin Silver, Kieran Suckling, and David Noah Greenwald of 
the Southwest Center for Biological Diversity on behalf of 22 groups to 
list the western yellow-billed cuckoo (Coccyzus americanus 
occidentalis). The 22 groups are the Maricopa Audubon Society, Tucson 
Audubon Society, Huachuca Audubon Society, White Mountain Audubon 
Society, the White Mountain Conservation League, Wildlife Damage 
Review, Sky Island Alliance, the San Pedro 100, the Zane Grey Chapter 
of Trout Unlimited, T & E Inc., the Biodiversity Legal Foundation, the 
Environmental Protection Information Center, the Sierra Nevada 
Alliance, the Wetlands Action Network, Rangewatch, the Oregon Natural 
Desert Association, the Oregon Natural Resources Center, the Klamath-
Siskiyou Wildlands Center, the Southern Utah Wilderness Alliance, the 
Wild Utah Forest Campaign, Friends of Nevada Wilderness, and the 
Toiyabe Chapter of the Sierra Club. The petitioners stated that they 
believe the yellow-billed cuckoo ``is endangered in a significant 
portion of its range (i.e., the western United States).'' The 
petitioners also stated they ``believe this range of endangerment is 
coterminous with a valid subspecies, the western yellow-billed cuckoo 
(Coccyzus americanus occidentalis),'' and that they would concur with a 
decision to list this taxon. Petitioners also requested that critical 
habitat be designated for the yellow-billed cuckoo concurrent with the 
listing, pursuant to 50 CFR 424.12 and the Administrative Procedures 
Act (5 U.S.C. 553). Included in the petition was supporting information 
on the species relating to taxonomy, ecology, adequacy of existing 
regulatory mechanisms, historic and present distribution, current 
status, and threats in the western United States.
    On February 17, 2000, we announced a 90-day petition finding in the 
Federal Register (65 FR 8104) concluding that the petition presented 
substantial scientific or commercial information to indicate that the 
listing of the western yellow-billed cuckoo may be warranted. In that 
finding, we also found that the petition did not present sufficient 
information to indicate that listing of the species as a whole may be 
warranted. In addition, the finding stated that the petition presented 
substantial information that led us to conclude that further 
investigation, through a status review, was required to determine the 
taxonomic validity of the western subspecies, and to determine if 
listing the western yellow-billed cuckoo as a distinct population 
segment (DPS) may be warranted.


    Ridgway (1887) separated the yellow-billed cuckoo into eastern and 
western subspecies, based on western birds being ``larger, with 
proportionately larger and stouter bill''. Wetmore (1968) added that 
western birds are slightly more gray above, and eastern birds more 
brown. Ridgway assigned birds from the area north and west from extreme 
west Texas to the Pacific Coast to the subspecies Coccyzus americanus 
occidentalis, and other cuckoos in North America to Coccyzus americanus 
americanus. Ridgway's western subspecies included birds from the Great 
Basin portions of Colorado and Wyoming, west and north to the Pacific 
Coast and southwestern British Columbia. The two subspecies were 
generally included in ornithological treatments through the 1960s 
(e.g., American Ornithologists Union (AOU) 1957; Oberholser and Kincaid 
    Many ornithologists, however, have questioned the separation of the 
species into two subspecies (Bent 1940; Monson and Phillips 1981; Van 
Tyne and Sutton 1937; Swarth 1929; Todd and Carriker 1922), citing the 
small magnitude and inconsistency of differences between eastern and 
western yellow-billed cuckoos, and the broad overlap in the size of 
eastern and western individuals. During this time, though, there was no 
systematic analysis of geographic variation to determine if there was 
an eastern and western yellow-billed cuckoo subspecies. Since 1983, AOU 
checklists (the recognized authority for taxonomy of North American 
birds) have not used subspecies names for any of the bird species in 
the checklist since the validity of many described avian subspecies 
needs to be evaluated, as does the potential for unrecognized 
subspecies (AOU 1983, 1998). The most recent checklist (AOU 1998) 
refers readers to the 1957 checklist for subspecies taxonomy, while 
noting the questionable validity of many subspecies. The AOU Checklist 
Committee (which makes taxonomic decisions for North American birds) 
has begun the process of reviewing the taxonomic status of subspecies 
for the North American families of birds, a task which is expected to 
take at least several years (R. Banks, chair of AOU Classification and 
Nomenclature Committee (North America), pers. comm., 1999).
    Yellow-billed cuckoo taxonomy was first reviewed in the late 1980s, 
when we requested that Dr. Banks, an avian taxonomist, evaluate the 
validity of the cuckoo subspecies. This request was in response to the 
1986 petition to list the yellow-billed cuckoo in the States of 
California, Washington, Oregon, Idaho, and Nevada. Banks compared three 
morphological characteristics (bill length, depth of upper mandible, 
and wing length) of almost 700 adult specimens of yellow-billed cuckoos 
and visually examined the colors of specimens. He found: (1) no pattern 
of geographic variation in color; (2) substantial overlap between 
eastern and western birds in wing length, bill length and mandible 
depth; and (3) no significant differences for these three 
characteristics. He concluded that the data did not justify the 
separation into eastern and western subspecies (Banks 1988). 
Subsequently, statistical errors were discovered in Bank's study 
(Spiller 1988), and a re-analysis of the same data indicated 
statistically significant differences between eastern and western 
yellow-billed cuckoos (p0.001) for the three characteristics measured 
by Banks. Banks published a correction to his earlier paper (Banks 
1990), acknowledging the computational error, but stating that the 
``statistical difference cannot be equated to a biological or practical 
difference.'' In support of this, he cited the small differences 
between mean measurements, the large degree of overlap between eastern 
and western birds in the ranges of measurements for the three 
characteristics he measured, and the sensitivity of the statistical 
procedure to detect very small differences as ``significant,'' given 
the large sample sizes. Banks concluded that his fundamental finding 
remained unchanged, that is, separation into subspecies was not 
warranted by the morphological data, and that all yellow-billed cuckoos 
in North America should be classified simply as Coccyzus americanus.
    Banks provided his data to two avian ecologists (Franzreb and 
Laymon 1993) who analyzed the same data set, supplemented by 
measurements for a fourth characteristic (tail length), and from a 
small number of additional

[[Page 38613]]

specimens of western birds. Franzreb and Laymon (1993) noted 
statistical errors by Banks (1988), finding that western birds are 
larger than eastern birds, and that one could separate a majority of 
western yellow-billed cuckoos from eastern yellow-billed cuckoos using 
discriminant analysis. Franzreb and Laymon (1993) also considered 
behavioral and ecological differences between western and eastern 
birds, and found evidence of differences in the timing of migration and 
breeding. They concluded that: (1) ``the recognition of subspecies on 
the basis of measurements of existing specimens is equivocal''; (2) 
study of geographical variation in vocalizations, bill color, and 
genetics was warranted; (3) the two subspecies should be retained 
pending the above studies; and (4) ``because the western yellow-billed 
cuckoo is so critically endangered * * * changes in its classification 
should be made only after the best possible study.'' Banks did not 
respond in print to their paper, but has stated that his conclusion 
remains unchanged (R. Banks, pers. comm., 1999).

Description and Natural History

    The yellow-billed cuckoo is a member of the avian family Cuculidae 
and order Cuculiformes. The approximate 128 members of Cuculidae share 
the common feature of a zygodactyl foot, in which two toes point 
forwards and two toes point backwards. Most species have moderate to 
heavy bills, somewhat elongated bodies, a ring of colored bare skin 
around the eye, and loose plumage. Six species of Cuculidae breed in 
the United States, two species of which breed west of the Continental 
Divide, the yellow-billed cuckoo and the greater roadrunner.
    The yellow-billed cuckoo is a medium-sized bird of about 30 
centimeters (cm) (12 inches (in.)) in length, and weighing about 60 
grams (2 ounces). The species has a slender, long-tailed profile, with 
a fairly stout and slightly down-curved bill which is blue-black with 
yellow on the base of the lower mandible. Plumage is grayish-brown 
above and white below, with red primary flight feathers. The tail 
feathers are boldly patterned with black and white below. The legs are 
short and bluish-gray, and adults have a narrow, yellow eye ring. 
Juveniles resemble adults, except the tail patterning is less distinct, 
and the lower bill may have little or no yellow.
    Mated males have a distinctive ``kowlp'' call which is a loud, 
nonmusical series of notes about 2-3 seconds long which slows down and 
slurs toward the end. Unmated males use a separate call which is an 
indeterminate series of soft notes ``coo-coo-coo-coo.'' Both members of 
a pair may give the ``knocker'' call, which is a harsh, rattled, series 
of notes (Hughes 1999).
    Western yellow-billed cuckoos breed in large blocks of riparian 
habitats (particularly woodlands with cottonwoods and willows), while 
eastern yellow-billed cuckoos breed in a wider range of habitats, 
including deciduous woodlands and parks (Ehrlich et al. 1988). Dense 
understory foliage appears to be an important factor in nest site 
selection, while cottonwood trees are an important foraging habitat in 
areas where the species has been studied in California (Laymon et al. 
1993). Clutch size is usually two or three eggs, and development of the 
young are very rapid, with a breeding cycle of 17 days from egg-laying 
to fledging of young. Although yellow-billed cuckoos usually raise 
their own young, they are facultative brood parasites, occasionally 
laying eggs in the nests of other yellow-billed cuckoos or of other 
bird species (Hughes 1997).
    Western yellow-billed cuckoos appear to require large blocks of 
riparian habitat for nesting. Along the Sacramento River in California, 
nesting yellow-billed cuckoos occupied home ranges which included 10 
hectares (ha) (25 acres (ac)) or more of riparian habitat (Gaines 1974; 
Laymon et al. 1993). Another study on the same river found riparian 
patches with yellow-billed cuckoo pairs to average 40 ha (99 ac) 
(Halterman 1991). Home ranges in the South Fork of the Kern River in 
California averaged about 17 ha (42 ac) (Laymon et al. 1993). Nesting 
densities ranging from 1 to 15 pairs per 40 ha (99 ac) were estimated 
in a New Mexico study (Howe 1986), and three plots in Arizona had 
densities ranging of 8.2, 19.8, and 26.5 pairs per 40 ha (99 ac) 
(Hughes 1999). Nesting west of the Continental Divide occurs almost 
exclusively close to water, and biologists have hypothesized that the 
species may be restricted to nesting in moist river bottoms in the west 
because of humidity requirements for successful hatching and rearing of 
young (Hamilton and Hamilton 1965; Rosenberg et al. 1991). Nesting 
peaks later (mid-June through August) than in most co-occurring bird 
species, and may be triggered by an abundance of the cicadas, katydids, 
caterpillars, or other large prey which form the bulk of the species' 
diet (Hamilton and Hamilton 1965; Rosenberg et al. 1982). The species 
is inconspicuous on its breeding range, except when calling to attract 
or to contact mates.


    The breeding range of the yellow-billed cuckoo formerly included 
most of North America from southern Canada to the Greater Antilles and 
northern Mexico (AOU 1957, 1998). In recent years, the species' 
distribution in the west has contracted. The northern limit of breeding 
in the coastal States is now in Sacramento Valley, California, and the 
northern limit of breeding in the western interior States is southern 
Idaho (AOU 1998; Hughes 1999). East of the Continental Divide, the 
species breeds from southeastern Montana, the Dakotas, Minnesota, 
southern Ontario, southeastern Quebec and probably southern New 
Brunswick south to eastern Colorado, Texas, the Gulf coast, 
northeastern Mexico, the Florida Keys, the Greater Antilles and the 
northern Lesser Antilles (AOU 1957, 1998). The species overwinters from 
Columbia and Venezuela, south to northern Argentina (Ehrlich et al. 
1992; AOU 1998). The extent to which yellow-billed cuckoos nesting in 
different regions of North America commingle during migration, or while 
overwintering, is unknown. Data provided by the U.S. Geological Survey-
Biological Resources Division, Bird Banding Laboratory (BBL), from bird 
band returns to date is insufficient to determine migration or 
wintering patterns (BBL, in litt., 1998).

Historic and Current Status

    The available data, including that provided by the petitioners, 
suggest that the yellow-billed cuckoo's range and population numbers 
have declined substantially across much of the western United States 
over the past 50 years. Analysis of population trends is difficult 
because quantitative data, including historical population estimates, 
are generally lacking. However, historic and recent data are sufficient 
to allow an evaluation of changes in the species' range in the western 
United States. Rough extrapolations, which use observed densities of 
yellow-billed cuckoos and historic habitat distribution, indicate that 
western populations were once substantial (Service 1985). The following 
discussion is based on information provided by the petition and in our 
files, and focuses on western North America, the area for which the 
petition provides information.
    Based on historic accounts, the species was widespread and locally 
common in California and Arizona, locally common in a few river reaches 
in New Mexico, common very locally in Oregon and Washington, generally 
local and uncommon in scattered drainages of

[[Page 38614]]

the arid and semiarid portions of western Colorado, western Wyoming, 
Idaho, Nevada, and Utah, and probably uncommon and very local in 
British Columbia. Hughes (1999) summarizes the species' historic range 
and status in these areas, which are described in detail below.
    In California prior to the 1930s, the species was widely 
distributed in suitable river bottom habitats, and was locally common 
(Grinnell and Miller 1944; Small 1994). Yellow-billed cuckoos nested 
primarily in coastal counties from San Diego County near the Mexico 
border to Sonoma County in the San Francisco Bay region, in the Central 
Valley from Kern County through Shasta County, and along the lower 
Colorado River (Grinnell and Miller 1944; Dawson 1923; Small 1994; 
Gaines and Laymon 1984). Yellow-billed cuckoos also bred locally 
elsewhere in the State, including in Inyo, San Bernardino, and Siskiyou 
counties (Grinnell and Miller 1944).
    The early literature relating to the yellow-billed cuckoo in 
California has been summarized and evaluated by Gaines (1974), Gaines 
and Laymon (1984), and Hughes (1999). Collectively they report dozens 
of locations where the species was historically reported and/or 
collected, sometimes in apparent abundance, but not subsequently found. 
Laymon and Halterman (1987b) estimated that in California the species' 
range was about 30 percent of its historical extent. Hughes (1999) 
provides an estimate of the California breeding population during the 
late 19th century of 15,000 pairs of breeding birds. Gaines (1974) 
believed that pre-development yellow-billed cuckoo populations in 
California were even greater than implied by the early literature, due 
to the species' inconspicious behavior and the fact that large tracts 
of floodplain riparian habitat had already been removed for development 
before the first records and accounts of the species began appearing in 
literature. Most modern investigators believe that a significant 
decline of the yellow-billed cuckoo in California occurred following 
the start of the major era of development beginning about the mid-1800s 
(Gaines and Laymon 1984; Laymon and Halterman 1987a, 1987b; Launer 
    The species was listed by the State of California as threatened in 
1971, and was reclassified as endangered in 1987. Based on a 1986-87 
Statewide survey, only three areas in the State support more than about 
five breeding pairs on a regular basis: The Sacramento River roughly 
between Colusa and Red Bluff; the South Fork of the Kern River upstream 
of Lake Isabella; and the lower Colorado River (Laymon and Halterman 
1987a, b). Laymon and Halterman (1987a) estimated 31-42 breeding pairs 
in the State, a decline of 66-81 percent from a 1977 survey (Gaines 
1974; Gaines and Laymon 1984). Along the lower Colorado River, on the 
California-Arizona border, Laymon and Halterman (1987a) estimated an 
80-90 percent decline by 1986 from an estimated 180-240 pairs in 1976-
1977, while Rosenberg et al. (1991) estimated a decline of 93 percent 
over this period, using an initial estimate of 242 pairs in 1976-1977. 
These declines coincided with habitat losses resulting from high water 
levels of long duration in 1983-1984 and 1986 (Laymon and Halterman 
1987b; Rosenberg et al. 1991). Final results from a Service-funded 1999 
State-wide survey indicate that yellow-billed cuckoo numbers in the 
Sacramento Valley and along the Kern River are comparable to numbers 
from the 1980s, while only two pairs were located on the California 
side of the Colorado River. No pairs were found in the part of the 
State west of the Colorado River and south of the Kern River (M. 
Halterman, Kern River Research Center, pers comm., 2001; Halterman et 
al. 2001). Although other biologists detected cuckoos at Prado Flood 
Control Basin, a pair on the Amargosa River, and a single cuckoo at the 
Mojave River near Victorville (Halterman et al., 2001), the lack of 
detections during the 1999 survey in these and other southern 
California areas where comparable previous surveys found cuckoos 
indicates population declines since the 1970s.
    An example of the species' decline in California is found in the 
San Joaquin Valley. Yellow-billed cuckoo have been recorded from every 
county in the San Joaquin Valley region except Kings County, and were 
locally common as a breeding bird at least in San Joaquin, Kern, 
Fresno, and Stanislaus counties (Gaines and Laymon 1984). Despite 
surveys for the species (Laymon and Halterman 1987a), there have been 
few records from the San Joaquin Valley since the 1960s. If the species 
still breeds there, the number of breeding pairs is very small (Gaines 
and Laymon 1984; Laymon and Halterman 1987a).
    In the Pacific Northwest, the species was formerly fairly common 
locally in willow bottoms along Willamette and Columbia Rivers in 
Oregon, and in the Puget Sound lowlands and along the lower Columbia 
River in Washington (Marshall 1996; Roberson 1980; Jewett et al. 1953; 
Gabrielson and Jewett, 1940). The species was also found locally in 
southeast British Columbia (Hughes 1999), but the available data are 
not adequate to determine historic abundance. The species was rare east 
of the Cascade Mountains in these states and provinces. The last 
confirmed breeding records were in the 1930s in Washington, and in the 
1940s in Oregon. It may now be extirpated from Washington. The species 
is ranked as critically imperiled as a breeding bird in Washington and 
is under review by the Washington Department of Fish and Wildlife for 
State listing (Washington Natural Heritage Program 1997).
    In Oregon, four yellow-billed cuckoo sightings were made west of 
the Cascade Mountains between 1970 and 1994. At least 20 records occur 
east of the Cascades (Gilligan 1994), and a few pairs may nest very 
locally in the eastern part of the State. A 1988 survey in eastern 
Oregon and Klamath County located no birds, but identified potential 
breeding habitat along the lower Owyhee River (Littlefield 1988). Most 
recent records were recorded in May and June of 1999 (Johnson et. al. 
2001), and a single yellow-billed cuckoo was sighted during the 
breeding season (June 26-27, 1999) along Bonita Road in Malheur County. 
It is believed that this species has been regularly sighted (without 
confirmed nesting) at the Malheur National Wildlife Refuge (B. 
Alterman, pers. comm., 2001).
    The species occurred in southwest British Columbia (Victoria, 
Kamloops, Chilliwack) (Bent 1940), but was apparently never common; the 
last confirmed breeding was in 1920s. The species has been recorded 
twice in British Columbia since the 1920s (Siddle 1992), and is 
considered extirpated (British Columbia Conservation Data Centre 1999; 
Hughes 1999).
    Arizona probably contains the largest remaining yellow-billed 
cuckoo population among States west of the Rocky Mountains. The species 
was historically widespread and locally common (Phillips et al. 1964; 
Monson and Phillips 1981; Groschupf 1987). One hundred sixty-eight 
yellow-billed cuckoo pairs and 80 single birds were located in Arizona 
in 1999, based on preliminary results from a State-wide survey which 
covered 427 km (265 mi) of river and creek bottoms (R. Magill, pers. 
comm., 1999). Based on these results, it is evident that yellow-billed 
cuckoo numbers in 1999 are substantially less than some previous 
estimates for Arizona, including a 1976 estimate of 846 pairs for the 
lower Colorado River and five major tributaries (Groschupf 1987). 
Losses of riparian habitats from historic levels have been substantial 
in Arizona (Noss

[[Page 38615]]

et al. 1995; Ohmart 1994; Rosenberg et al. 1991). Losses have been 
greatest at lower elevations (below about 900 m (3,000 ft) elevation) 
along the Lower Colorado River and its major tributaries, which have 
been strongly affected by upstream dams, flow alterations, channel 
modification, and clearing of land for agriculture (Groschupf 1987). As 
habitat has declined, yellow-billed cuckoo numbers have likely 
declined, as has been documented for the lower Colorado River 
(Rosenberg et al. 1991), and described above for California. Following 
the high water levels of 1983-1984 and 1986, yellow-billed cuckoo 
numbers also declined by 70-75 percent on the Bill Williams River 
delta, which abuts the lower Colorado River (Rosenberg et al. 1991). 
Habitat has since recovered on the Bill Williams River delta, but 
yellow-billed cuckoo numbers remain low (M. Halterman, pers. comm., 
1999). In some Arizona areas, such as the San Pedro Riparian National 
Conservation Area along about 65 km (40 mi) of the upper San Pedro 
River, ongoing conservation efforts may improve habitat conditions for 
the species. The species is considered a Species of Concern by the 
Arizona Game and Fish Department, a designation which does not provide 
protection to the species (T. Corman, Arizona Game and Fish Department, 
pers. comm., 1999).
    In Colorado, west of the Continental Divide, the species was 
probably never common (Bailey and Niedrach 1965; Kingery 1998), and is 
now extremely rare (Kingery 1998). The yellow-billed cuckoo is an 
uncommon summer resident of Colorado. According to the Colorado 
Breeding Atlas (Kingery 1998), the general status of the yellow-billed 
cuckoo in Colorado is that it is nearly extirpated, with once common 
eastern populations becoming uncommon to rare. Only one confirmed 
nesting observation occurred along the Yampa River near Hayden during 
the Breeding Bird Atlas surveys conducted from 1987-1994. Other 
confirmed nesting records (mid 1980s) have been associated with 
outbreaks of caterpillar infestations in box elders (Acer negundo) in 
the Four Corners Region/Durango area. However, over recent years , the 
use of insecticides and the removal of box elders has reduced the 
outbreaks of insect infestations, resulting in fewer occurrences of 
yellow-billed cuckoo in the area (Dr. Albert Spencer in Marylin Colyer, 
in litt., 2001).
    National Park Service (NPS) surveys in southwest Colorado, from 
1988 through 1995 for the Colorado Bird Breeding Atlas, found no 
records of yellow-billed cuckoo. Park staff also conducted extensive 
surveys of the Mancos River in the park six times during the past 12 
years and adjacent to Yucca House National Monument throughout 2000 
with no reports of yellow-billed cuckoos (Marylin Colyer, in litt., 
2001). Few sightings of the yellow-billed cuckoo have occurred in 
western Colorado along the Colorado River near Grand Junction (Terry 
Ireland, Service, pers. comm., 2001). In 1998, biologists surveyed 387 
km (242 mi) of lowland river riparian habitat along six rivers in west-
central Colorado for yellow-billed cuckoos, finding one individual bird 
(Dexter 1998).
    There is very limited data for the area west of the Continental 
Divide in Montana. Three specimens of the yellow-billed cuckoo have 
been collected since the early 1960s, and there are few recorded 
sightings of the yellow-billed cuckoo since the early 1900s (Saunders 
1921). Local records for the species around the Flathead River area are 
scarce and there have been a few records which indicate that they do 
occur in this area, but no confirmed breeding information exists (S. 
Lenard, Montana Audubon, pers. comm., 2001). Yellow-billed cuckoos may 
be seen locally in the southern portion of the State along the larger 
stream corridors that run from Montana into northeastern Wyoming (L. 
Nordstrom, Service, pers. comm., 2001).
    In Idaho, the species was considered a rare and local summer 
resident (Burleigh 1972). In northern and central Idaho, there have 
only been four records of yellow-billed cuckoo over the last century 
(Taylor 2000). The most recent record for this area comes from the 
South Fork of the Snake River in 1992 (Stephens and Sturts 1997). In 
southwestern Idaho, the yellow-billed cuckoo has been considered a 
rare, sometimes erratic, visitor and breeder in the Snake River valley. 
Numerous sightings have been recorded in the southwestern part of the 
State during the past 25 years. The yellow-billed cuckoo appears to be 
hanging on precariously in Idaho and could easily become extirpated 
from the State in the near future. The available information is 
inadequate to judge population or distributional trends, and the 
breeding population in Idaho is likely limited to a few breeding pairs, 
at most.
    The historic status of the yellow-billed cuckoo in Nevada is poorly 
documented, although there is evidence it was nesting along the lower 
Truckee and Carson Rivers and in southern Nevada along the Colorado and 
Virgin Rivers (Linsdale 1951; Neel 1999). Surveys using call-playback 
techniques were done in the early 1970s along the Truckee, Carson, and 
Walker Rivers. The surveys of the six remaining habitats able to 
support yellow-billed cuckoos, as described by Gaines (1974), resulted 
in no birds being heard or seen (Oakleaf 1974). The most recent 
documentation of the yellow-billed cuckoo nesting in Nevada was a pair 
at Beaver Dam Wash, Lincoln County in 1979. Since 1990, there have been 
only sporadic sightings of single birds throughout the State (Neel 
1999). The Nevada Division of Wildlife (NDW) (2001) conducted surveys 
in 2000 in southern Nevada and documented 19 yellow-billed cuckoo, 
comprising 4 pairs and 11 unpaired birds with no nests being found. An 
estimate by the NDW put the summer population of yellow-billed cuckoo 
between 20-30 birds State-wide.
    Suitable habitat for the yellow-billed cuckoo is very limited in 
Nevada, with most areas of cottonwood riparian forests being fragmented 
(NDW, in litt., 2001). NPS studies from Great Basin National Park (NPS, 
in litt., 2001) in the South Snake Mountain Range determined that of 
the 190 ha (469 ac) of existing riparian habitat only 3 ha (8 ac) was 
suitable for supporting yellow-billed cuckoo. Most of the suitable 
habitat along the Truckee, Carson, and Walker Rivers has been modified 
or destroyed (NDW, in litt., 1985, 1990).
    The decline of the yellow-billed cuckoo in Clark County, Nevada has 
been attributed to the reduction or degradation of riparian habitat, 
river channelization, livestock grazing, use of pesticides, non-native 
plant encroachment (tamarisk), and brown-headed cowbird parasitism 
(Clark County 2000). The State of Nevada has listed the yellow-billed 
cuckoo as State Rank S1 Nevada State Protected. This means that the 
species is protected in Nevada and is considered critically imperiled 
due to extreme rarity, imminent threats, and/or biological factors. 
Under such a designation, the protected species may not be killed, 
captured, shot at, trapped, wounded, possessed, collected, seined, or 
netted, nor can a person attempt to do any of these activities.
    In Wyoming, population status and trends of yellow-billed cuckoos 
are unknown (Wyoming Game and Fish Department 1999). Remaining suitable 
cottonwood riparian habitat for this species is very limited in 
distribution in the State and is not adequately surveyed. Within the 
DPS identified in this finding, breeding activity is considered 
unconfirmed but observations and other anecdotal evidence suggests that 
breeding may

[[Page 38616]]

occur within the Green River Basin and along the Snake River within the 
State (P. Deibert, Service, pers. comm., 2001).
    In New Mexico, the species was historically rare State-wide, but 
common in riparian areas along the Pecos and Rio Grande Rivers, as well 
as uncommon to common locally along portions of the Gila, San Francisco 
and San Juan Rivers (Hubbard 1978; Bailey 1928). Current information is 
inadequate to judge trends, but the species was fairly common in the 
mid-1980s along the Rio Grande River between Albuquerque and Elephant 
Butte Reservoir, and along the Pecos River in southeastern New Mexico. 
Numbers may have increased there in response to tamarisk (Tamarix 
species) colonization of riparian areas formerly devoid of riparian 
vegetation (Howe 1986). A review on the status of the species in New 
Mexico concluded that the species would likely experience future 
declines in the State due to loss of riparian woodlands (Howe 1986). 
Riparian habitat degradation and/or loss of cottonwood regeneration are 
likely occurring in some areas. Along the Rio Grande, water and flood 
control projects have altered flow regimes and river dynamics, 
inhibiting regeneration of cottonwood-willow riparian habitats. 
Elsewhere in the State, grazing also contributes to degradation and 
loss of riparian habitats. The future degradation and loss of such 
riparian vegetation would limit the amount of habitat available for the 
cuckoo (B. Howe, Service, pers. comm., 1999).
    The portion of Texas west of the Pecos River has been identified as 
within the range of the historic western subspecies (Oberholser and 
Kincaid 1974), but other authors consider birds from this area most 
similar to eastern yellow-billed cuckoos (Hughes 1999). The species 
still occurs in this area, but its conservation status is unknown 
(Groschupf 1987). Population reports of the yellow-billed cuckoo in the 
trans-Pecos area of western Texas near Big Bend National Park indicate 
that the area supports scattered populations of yellow-billed cuckoo 
(Wauer 1971). These populations tend to be associated with areas of 
springs and developed wells or earthen ponds supporting mesic 
vegetation such as cottonwood and willow. The bird checklist of 
Guadalupe Mountains National Park near Beaumont Texas on the New Mexico 
border lists the yellow-billed cuckoo as a rare summer and fall 
breeder. Yellow-billed cuckoo population trends from 1966 to 1998 for 
the entire State of Texas are showing a decline (BBL 1999; Service 
1989). Yellow-billed cuckoo call studies from the University of Texas 
at El Paso, conducted from 1988 to 1998, noticed a significant decline 
in response calls over numerous sites in southern New Mexico and 
western Texas. Average response percentages went from 30 percent in 
1988 to 5 percent in 1998. The study concluded that based on the 
results of the surveys the yellow-billed cuckoo is a rare and highly 
vulnerable species in the Rio Grande Valley of Southern New Mexico and 
extreme west Texas (J. Sproul, University of Texas-El Paso, in litt., 
2000). The Texas Department of Parks and Wildlife (TDPW) currently does 
not separate the eastern and western populations of the yellow-billed 
cuckoo and identifies the species as globally abundant and State secure 
since the State ranking was last revised in 1994. However, subsequent 
publications by the TDPW, suggest the species is becoming increasingly 
rare and declining due to urban development and reduction of habitat 
(Shakelford and Lockwood 2000). Peterson and Zimmer (1998) reported 
that the yellow-billed cuckoo may be declining due to habitat 
destruction in El Paso County. The species is considered to be 
widespread and uncommon to common in central and eastern Texas 
(Oberholser and Kincaid 1974; Rappole and Blacklock 1994).
    In Utah, the species was historically uncommon to rare along river 
bottoms. There are at least two recent breeding records (Ouray National 
Wildlife Refuge on the Green River in 1992; and the Matheson Wetland 
Preserve near Moab in 1994, L. Romin, Service, pers. comm., 2000), and 
reports from at least five other areas where breeding has been 
suspected (E. Owens, Service, pers. comm., 1998). Recent avian surveys 
of riparian habitats within the historic range (the Salt Lake Valley) 
recorded three yellow-billed cuckoos in 7,000 survey hours (E. Owens, 
pers. comm., 1998). Threats to yellow-billed cuckoos and their habitat 
along the Green River in Utah include habitat loss and fragmentation 
from flooding and dewatering, encroachment by non-native tamarisk, 
grazing, and oil and gas development (Hanberg 2000 in Howe and Hanberg 
2000). Management of flow regimes was identified as a major impact on 
habitat with extremely high flows removing habitat, and extended 
periods of low flows likely drying up yellow-billed cuckoo habitat, 
which could result in the loss of suitable habitat and invasion by 
tamarisk. Cattle grazing also was identified as a possible threat to 
yellow-billed cuckoo habitat by contributing to the loss of subcanopy 
vegetation and cottonwood regeneration by grazing and trampling. 
Another potential threat to yellow-billed cuckoo habitat was attributed 
to recreational impacts by river users (e.g., use of cottonwood stands 
for campsites and ``lunch spots''). The Utah Division of Wildlife 
Resources (1998) stated that the yellow-billed cuckoo is threatened by 
habitat loss from agricultural, water, road and urban development, and 
has declined significantly across its range.
    In the United States east of the Rocky Mountains, the yellow-billed 
cuckoo is uncommon to common as a breeding bird. The species' habitat 
in this region, riparian and other broad-leaved woodlands (Ehrlich et 
al. 1988), occupy a significant area of the region (Service 1981). This 
is in sharp contrast to the west, where suitable habitat is limited to 
narrow and often widely separated riparian zones that occupy less than 
one percent of the western landscape (Service 1981; Knopf and Samson 
    Trend data based on detections by the Breeding Bird Survey (BBS) 
program (BBS 1999) indicate significant population declines between 
1966 and 1996 in 12 of 29 eastern and central States; the average 
annual decline during this period was 1.9 percent. Most of these 
declines have occurred since 1980. The average number of detections of 
yellow-billed cuckoos increased in these 29 States for the interval 
from 1966 to 1979; however, the average number of detections decreased 
in all 29 States between 1980 and 1996. In 15 of these States, the 
decline between 1980 and 1996 is statistically significant. The average 
annual decline during this period was 2.8 percent. Trends vary widely 
between States, ranging from a decline of 15.8 percent (Connecticut, 
1966-1996) to an increase of 17 percent (Nebraska, 1966-1979). Bird 
survey data are insufficient to evaluate population trends in regions 
west of the Continental Divide, but do provide data for two Service 
regions which span both sides of the Divide. The BBS data indicate 
declines of 2.7 percent in Region 2 (Arizona, Oklahoma, Texas, and New 
Mexico; 1980-1996), and 4.7 percent in Region 6 (Kansas, Nebraska, the 
Dakotas, Montana, Colorado, Utah, and Wyoming; 1980-1996).
    The species breeds locally in Mexico, and is a widespread transient 
during migration (Howell and Webb 1995). The species has been recorded 
as a summer resident (presumably breeding) locally within several 
regions of Mexico, including the State of Baja California Sur; 
northwest Mexico from Sonora and Chihuahua south to Zacatecas; 
northeast Mexico on the Atlantic slope from Coahuila to Tamaulipas; and 
in the northern Yucatan Peninsula (Howell

[[Page 38617]]

and Webb 1995). The species has been recorded as locally common in the 
state of Sonora (Russell and Monson 1998), but recent or quantitative 
information for that area is lacking (L. Hays, Service, pers. comm., 
1999), as is data on the status of yellow-billed cuckoo populations in 

Previous Federal Action

    In 1986, we were petitioned to list the yellow-billed cuckoo as 
endangered in the States of California, Washington, Oregon, Idaho, and 
Nevada (Manolis et al. 1986). We received this petition from Dr. Tim 
Manolis, Western Field Ornithologists, and it was co-signed by the 
Animal Protection Institute, Defenders of Wildlife, Sacramento River 
Preservation Trust, Friends of the River, Planning and Conservation 
League, Davis Audubon Society, Sacramento Audubon Society, and the 
Sierra Club. We published a 90-day finding on January 21, 1987, in the 
Federal Register, stating that the petition presented substantial 
information indicating that the requested action may be warranted (52 
FR 2239). In that finding, we acknowledged difficulties in defining a 
distinct, biologically defensible population of the western yellow-
billed cuckoo for possible listing, and that there were gaps in 
available information as to its status in certain parts of its range. 
We published a 12-month finding on December 29, 1988, in the Federal 
Register (53 FR 52746), stating that the petitioned action was not 
warranted, finding that the petitioned area did not encompass either a 
distinct subspecies or a distinct population segment. The finding 
cited: (1) A study by Dr. Richard C. Banks (1988) which concluded that 
the morphological differences between eastern and western birds were 
too small to merit separate subspecies, and (2) a lack of distinctness 
for the petitioned ``population,'' noting that yellow-billed cuckoos 
nest along the Arizona-California border on the lower Colorado River. 
This indicated that the California population in that area is not 
distinct, and that if the species was listed per the petition, listed 
California birds could not be distinguished or separate from unlisted 
Arizona birds.
    On February 9, 1998, we received a petition, dated February 2, 
1998, from the Southwest Center for Biological Diversity on behalf of 
22 groups. The petitioners requested us to list the yellow-billed 
cuckoo, stating that they believe the species ``is endangered in a 
significant portion of its range (i.e., the western United States).'' 
The petitioners also stated they ``believe this range of endangerment 
is coterminous with a valid subspecies the western yellow-billed cuckoo 
(Coccyzus americanus occidentalis),'' and that they would concur with a 
decision to list this taxon. Included in the petition was supporting 
information on the species relating to taxonomy, ecology, and adequacy 
of existing regulatory mechanisms, and historic and present 
distribution, current status, and threats in the western United States.
    On February 17, 2000, we announced a 90-day petition finding (65 FR 
8104) concluding that the petition presented substantial scientific or 
commercial information to indicate that the listing of the western 
yellow-billed cuckoo may be warranted. In that finding, we also found 
that the petition did not present sufficient information to indicate 
that listing of the species as a whole may be warranted. Our 90-day 
finding concluded that the available information did not resolve the 
issue of the validity of separating the yellow-billed cuckoo into two 
subspecies, but that further investigation, through a status review, 
was required to determine the taxonomic validity of the western 
subspecies, and to determine if listing the western yellow-billed 
cuckoo as a DPS may be warranted.
    Since publication of the finding, we have gathered additional 
information, as a result of three actions: (1) We asked the AOU 
Committee on Classification and Nomenclature (Committee) to review the 
available information, particularly the published taxonomic studies of 
Banks (1988, 1990) and Franzreb and Laymon (1993), and to make a 
recommendation as to the validity of the yellow-billed cuckoo 
subspecies; (2) we funded an analysis of the geographic variation in 
population genetics throughout the species' United States range, 
conducted by Dr. Robert C. Fleischer, head of the Molecular Genetics 
Laboratory of the Smithsonian Institution; and (3) we solicited, in our 
90-day finding, and during two open comment periods, information 
regarding the taxonomic status of the species, information on 
behavioral and ecological differences between eastern and western 
yellow-billed cuckoos, and other information which might aid in 
differentiating population segments.
    In a letter dated March 10, 2000, we requested the Committee's 
review of the taxonomic validity of the subspecies, and indicated that 
this would greatly assist us in preparing the 12-month finding, which 
would address the potential conservation needs of the species (Service, 
in litt., 2000). The Committee, consisting of six professional North 
American ornithologists, responded in a letter dated November 17, 2000. 
They agreed with Dr. Bank's original 1988 conclusion that the yellow-
billed cuckoo should be considered monotypic, that is, the named 
western form C. a. occidentalis is not a recognizably distinct 
subspecies. The Committee went on to say that they believe that the 
differences between the western populations and those in the rest of 
the range of the species are so small and the degree of overlap so 
great as to preclude separation at any level compatible with 
recognition of a subspecies (Committee, in litt., 2000).
    On January 14, 2000, the Service and United States Geological 
Service (USGS) solicited proposals via a market survey, for a genetic 
analysis throughout the species breeding range in the United States and 
Mexico (USGS, in litt., 2000). We wanted to determine if a valid 
subspecies or DPS exists for the yellow-billed cuckoo, and for which a 
listing proposal could be supported under the Act. From a total of five 
proposals received, we selected and funded a proposal submitted by Dr. 
Robert Fleischer. We received the final genetics study prepared by Dr. 
Fleischer on April 24, 2001. In the report, Dr. Fleischer concluded 
from his analysis of two mitochondrial genes (ATPase 8 and the control 
region) sequenced from 66 yellow-billed cuckoos samples across the 
continental United States and Mexico, that no valid subspecies exists 
(R. Fleischer, in litt., 2001).
    On June 5, 2001, we announced in the Federal Register (66 FR 
30148), the Notice of Availability of Dr. Fleischer's report, reopened 
the comment period until June 20, 2001, and sent the report to six 
professionals in the field of population genetics, or knowledgeable of 
the life history and distribution of the yellow-billed cuckoo in North 
America for peer review. The individuals and institutions which were 
asked to review the study included: Dr. George Barrowclough of the 
American Museum of Natural History, New York, NY; Dr. Susan Haig of the 
USGS Forest and Rangeland Ecosystem Science Center; Dr. Eben Paxton of 
the USGS Colorado Plateau Field Station; Dr. Allen Barker of the Royal 
Ontario Museum, Ontario, Canada; Dr. Robert Zink, University of 
Minnesota; and Dr. Oliver Ryder of the Center for Reproduction of 
Endangered Species, San Diego CA. We received three responses to the 
six inquiries for review within the comment period. These responses 
were from Dr. George Barrowclough; Dr. Susan Haig; and Dr. Oliver 
    During this comment period, we received additional review of the 
study from individuals in the field of

[[Page 38618]]

population genetics. These individuals included: Dr. Peter Stacey of 
the University of New Mexico; Dr. Leo Joseph of the Academy of Natural 
Sciences Philadelphia, Pennsylvania; Dr. Phil Hedrick of Arizona State 
University; and Dr. Martin Taylor of the Center for Biological 
Diversity. We also received comments from the Wyoming Department of 
Game and Fish. All three of the peer reviewers, and the five reviewers 
sending additional comments, acknowledged Dr. Fleischer's determination 
from his study that there was a general lack of differentiation between 
the eastern and western populations of yellow-billed cuckoo. However, 
three individuals concluded that there was evidence which suggested 
that the yellow-billed cuckoo has undergone a recent range expansion 
and appears to have separated from each other in the relatively recent 
past. All of the reviews, except that of Dr. George Barrowclough, Dr. 
Susan Haig, and Wyoming Department of Game and Fish, stated that the 
use of mitochondrial DNA (mtDNA) sequences for markers would not 
necessarily show more recent diversions of populations since mtDNA 
evolve more slowly, and that perhaps other genetic markers would.
    Since February 17, 2000, when the first open comment period was 
announced for the 90-day finding on the petition, we have received 
information from the public as a result of a mass mailing to over 2,500 
individuals including Federal, State and local agencies and Tribes 
throughout North America. This list was partially created from the 45th 
edition of the Conservation Directory published annually by the 
National Wildlife Federation, and The Flock (a biennial membership 
directory for several North American ornithological societies; The 
Association of Field Ornithologists, The Waterbird Society, The Cooper 
Ornithological Society, The Raptor Research Foundation, and The Wilson 
Ornithological Society). We received over 100 responses from agencies 
and individuals in the form of letters, reports, survey information and 
e-mails. We also received additional information from Dr. Steve Laymon, 
one of the petitioners (S. Laymon, in. litt., 2000). This information 
consisted of additional biological, behavioral, and ecological data and 
professional correspondence on the yellow-billed cuckoo in support of 
the petition.
    This 12-month finding is made in accordance with a court order 
which requires us to complete a finding by July 19, 2001 (Southwest 
Center for Biological Diversity v. Badgley et al. (No. 00-1045-KI 

Distinct Vertebrate Population Segment

    Under the Act, we must consider for listing any species, 
subspecies, or, for vertebrates, any DPS of these taxa if there is 
sufficient information to indicate that such action may be warranted. 
To implement the measures prescribed by the Act and its Congressional 
guidance, we (along with the National Marine Fisheries Service) 
developed policy that addresses the recognition of DPSs for potential 
listing actions (61 FR 4722). The policy allows for more refined 
application of the Act that better reflects the biological needs of the 
taxon being considered and avoids the inclusion of entities that do not 
require its protective measures.
    Under our DPS policy, we use two elements to assess whether a 
population segment under consideration for listing may be recognized as 
a DPS. The elements are: (1) The population segment's discreteness from 
the remainder of the taxon, and (2) the population segment's 
significance to the taxon to which it belongs. If we determine that a 
population segment being considered for listing represents a DPS, then 
the level of threat to the population segment is evaluated based on the 
five listing factors established by the Act to determine if listing it 
as either threatened or endangered is warranted.
    Below, we address under our DPS policy the population segment of 
yellow-billed cuckoos that occurs in the western United States. The 
area for this DPS would be the area west of the crest of the Rocky 
Mountains. For the northern tier of Rocky Mountain States (Montana, 
Wyoming, northern and central Colorado), the crest coincides with the 
Continental Divide. In the southern Colorado and New Mexico the crest 
coincides with the eastern boundary of the Rio Grande drainage, 
including the Sangre de Cristo Mountains and excluding the drainage of 
the Pecos River. In west Texas the DPS boundary is the line of mountain 
ranges that form a southeastern extension of the Rocky Mountains to the 
Big Bend area of west Texas, and which form the western boundary of the 
Pecos River drainage.


    A population segment of a vertebrate species may be considered 
discrete if it satisfies either one of the following two 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; and (2) it is 
delimited by international governmental boundaries within which 
significant differences in control of exploitation, management of 
habitat, conservation status, or regulatory mechanisms exist.
    The proposed DPS is based primarily on the first of the those two 
conditions, the marked separation from other populations. In addition, 
the northern and southern boundaries of the proposed DPS are the 
international boundaries with Canada and with Mexico. Although observed 
locally into British Columbia, Canada, in the early 1900s, the yellow-
billed cuckoo is believed to have been extirpated from that province 
(AOU 1998; Hughes 1999).
    The status of the yellow-billed cuckoo in Mexico is of great 
concern because most of its habitat is privately or communally owned, 
and severe degradation has occurred and continues to occur from 
grazing, wood cutting, recreation, and agricultural practices (Robert 
Mesta, Service, in litt., 2001). In addition, the yellow-billed cuckoo 
is not officially protected by the Mexican government, there are no 
Federal laws which require mitigation for loss or destruction of 
habitat, and there is little authority on private and communal lands to 
protect and manage for the yellow-billed cuckoo without the consent and 
cooperation of the landowners (R. Mesta, in litt., 2001). The DPS 
policy allows us to delimit the boundaries of a DPS by international 
boundaries where 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. For the reasons 
stated above, we believe that these factors collectively play a role in 
delimiting the southern DPS boundary along the international border 
with Mexico from the Big Bend area of Texas westward to the Pacific 
    We recognize that yellow-billed cuckoos within the described DPS 
are not wholly isolated from eastern yellow-billed cuckoo populations 
by the Rocky Mountain crest in west Texas, and to a lesser extent, 
further north. As discussed elsewhere, recent genetic data do not 
support separation of the yellow-billed cuckoo into eastern and western 
subspecies. Our DPS policy explicitly states that complete reproductive 
isolation is not required to recognize discreteness of a DPS, and DPS 
recognition can be appropriate where differences between populations 
are not sufficiently large to merit recognition of subspecies. Several 
lines of evidence contributed to our conclusion that the

[[Page 38619]]

population of yellow-billed cuckoos west of the Rocky Mountain crest 
meets the discreteness criteria. This evidence is discussed below.

Physical Discreteness

    Yellow-billed cuckoos breed on both sides of the crest of the Rocky 
Mountains where suitable habitat occurs (Johnsgard 1986). Although the 
Rocky Mountains may not wholly prevent movement of yellow-billed 
cuckoos across the Rocky Mountain crest, the available information 
indicates that the Rocky Mountains substantially separate yellow-billed 
cuckoo populations occurring east and west of their crest. In this 
section, we relate the pattern of yellow-billed cuckoo distribution to 
geographic and other physical factors. Physical factors also interact 
with ecological factors, as altitudinal, topographic, and climatic 
factors influence the distribution of suitable habitat for nesting 
yellow-billed cuckoos. We address these interactions in the following 
section on ecological discreteness.
    The eastern boundary of the western DPS spans a distance of about 
2,400 kilometers (km) (1,500 miles (mi)), from the Montana-Canada 
border to the Texas-Mexico border in the Big Bend area. As will be 
detailed below, the degree of separation varies from north to south, 
but is substantial along more than 87 percent of the boundary, 
encompassing the DPS boundary from the Canada border to southern New 
Mexico. From the Canada border to the southern end of the Sangre de 
Cristo Mountains in northern New Mexico, a distance of about 1,700 km 
(1,050 mi), nesting birds and habitat in the western DPS are separated 
physically from nesting yellow-billed cuckoo populations in the east by 
an extensive high elevation zone of the Rocky Mountains, and/or by 
extensive areas where records of cuckoos, and cuckoo habitat, are very 
sparse. This barrier becomes less defined for the small area of 
northern Santa Fe County and western Mora and San Miguel counties. In 
this area, cuckoos in the western DPS breed along the Rio Grande near 
Los Alamos, while its assumed that eastern cuckoos nest as little as 
100 km (60 mi) to the east along the Mora and upper Pecos Rivers 
(Hubbard 1978; Howe 1986). However, eastern cuckoo records in this area 
of proximity are few, and the areas of regular cuckoo occurrence (Howe 
1986) remain separated by about 200 km (124 mi).
    Just to the south of the Sangre de Cristo Mountains, the area of 
separation broadens again. From here to the New Mexico-Texas border is 
about 380 km (236 mi), and a broad band, about 160 km (100 miles) east-
west, supports little cuckoo habitat and has very few cuckoo records. 
The lone exception is a small, isolated riparian area near Alamogordo, 
where cuckoos regularly occur (Howell 1986). This southern New Mexico 
zone of separation includes extensive highlands and mountains exceeding 
1,800 meters (m) (6,000 feet (ft)) elevation, as well as the desert 
basin between the Rio Grande and Sacramento Mountains.
    In west Texas and southern New Mexico, the physical separation is 
less marked, where the Rocky Mountains become a series of relatively 
low, isolated ranges within a high plateau, stretching between the 
Guadalupe Mountains on the Texas-New Mexico border to the Chisos 
Mountains in the Big Bend National Park, on the border with Mexico. In 
this region, the DPS boundary and the separation between eastern and 
western birds may be less complete than for the rest of the DPS. In our 
administrative finding for our 90-day finding for this petition (65 FR 
8104), we noted the lack of a barrier between the Rio Grande and Gila 
River drainages in southern New Mexico. This problem is addressed by 
the DPS boundary, which includes both of these drainages, for reasons 
described above. The affinity of yellow-billed cuckoos from west Texas 
is still problematic, however, in that the Pecos River drainage is not 
strongly separated from the Rio Grande drainage upstream of the Big 
Bend, and yellow-billed cuckoo movement and interchange across the DPS 
boundary is expected to be greater in this region than along the rest 
of the DPS boundary. Such interchange and resulting diffusing of 
differences may be the reason why west Texas yellow-billed cuckoos have 
been reported to be morphologically aligned with both eastern yellow-
billed cuckoo populations (Hughes 1999) and with western yellow-billed 
cuckoos. The majority of the available information, including timing of 
nesting, indicates that birds from Texas west of the Pecos River and 
from the Big Bend upstream exhibit greater similarity to western 
yellow-billed cuckoos (Wauer 1973; Oberholser and Kincaid 1974; 
Franzreb and Laymon 1993; J. Sproul, in litt., 2001). Considering these 
factors, along with the information on physical factors, we have 
included west Texas within the western DPS.
    In the northern Rocky Mountains and northern Great Plains, from the 
Canada border south through Colorado, the yellow-billed cuckoo is 
``extremely rare and local'' as a breeding bird (Hughes 1999). While 
the species breeds locally in southeast Montana, southern Idaho, 
northeast and southwest Wyoming, west Colorado, and Utah (Hughes 1999), 
it is quite rare or absent within the higher Rocky Mountains. An 
examination of the distributional records for the Rocky Mountain region 
indicates that within this area of few yellow-billed cuckoos, the 
species is even more scarce at elevations above approximately 2,000 m 
(6,600 ft). Most sources describe the species' range as extending up to 
this elevation (often described as occurring in the Sonoran Life Zones 
in older works) (Bailey 1928; Bailey and Niedrach 1965; Phillips et. 
al. 1964; Johnsgard 1986; Corman and McGill 2000; Hanberg 2000; M. 
Long, Service, pers. comm., 2001).
    Within western Montana and southern Wyoming, the Rocky Mountain 
crest is less marked. In western Montana, the unoccupied region 
includes the area west of the Continental Divide, and extends into the 
panhandle of northern Idaho. The high elevation zone in western Montana 
narrows to a width of 80 km (50 mi) and sometimes less, where deep 
river valleys of the Columbia River drainage cut through the high 
mountains. However, the scarcity of records from this region indicates 
that nesting west of the Continental Divide in Montana is at most very 
limited and sporadic (Hughes 1999; P. Hendricks, Montana Natural 
Heritage Program, in litt., 2001), and the region of effective 
separation in Montana may be as wide as 800 km (500 mi) (S. Laymon, in. 
litt., 2000). Coupled with the rarity of yellow-billed cuckoos in 
adjacent areas to the west and east, the available information 
indicates that the Rocky Mountain region in Montana and northern Idaho 
forms a wide break between yellow-billed cuckoo populations to the east 
and west.
    Suitable habitat in Wyoming is limited to Park, Fremont, western 
Hot Springs, and central and eastern Sweetwater counties. However, 
there is no data which suggests these areas are occupied by yellow-
billed cuckoos (P. Deibert, pers. comm., 2001). In southern Wyoming, 
the crest of the Rocky Mountains dips to near 2,300 m (7,500 ft) to the 
southeast of the Wind River Range. In this area, the Great Divide Basin 
forms a high, internal basin which separates the Snake River drainage 
from the Missouri River drainage. This basin, while not a physical 
barrier topographically, is a high desert lacking in yellow-billed 
cuckoo habitat (P. Deibert, pers. comm., 2001; T. Collins, Wyoming Game 
and Fish Department, pers. comm., 2001). The basin consists mostly of 
rolling plains, extensive playas and dune fields that receives 2.25

[[Page 38620]]

cm (0.9 in.) of precipitation annually (Reiners and Thurston 1996). 
Although this lower area may be less of a physical barrier to birds, 
reported yellow-billed cuckoo sites to the east and west in this area 
are separated by about 240 km (150 mi) of unsuitable habitat, as is 
true for the rest of the Rocky Mountains' crest from the Montana to 
Colorado border (Reiners and Thurston 1996; Wyoming Game and Fish, in 
litt., 2001). Therefore, we find that the appropriate DPS boundary is 
that which encompasses the Snake River basin, as it follows the 
southern and western edge of the Great Divide Basin.
    In Colorado, the band of high-elevation is over 150 km (100 mi) 
wide along the entire north-south axis of the Rocky Mountains. The 
available data indicate that yellow-billed cuckoos was probably never 
common on the western slope of the Rocky Mountains in Colorado (Bailey 
and Niedrach 1965; Kingery 1998), and is now extremely rare (Kingery 
1998). Based on the available information, the Rocky Mountains in 
Colorado form a substantial break between yellow-billed cuckoo 
populations east and west of the crest, a break which is accentuated by 
the species' current extreme rarity in Colorado west of the Great 
    The separation of western and eastern populations of yellow-billed 
cuckoo continues south along the Rocky Mountain crest into Southern 
Colorado, eastern New Mexico and southwest Texas, terminating at the 
Rio Grande river in the Big Bend National Park. Thus, the western 
yellow-billed cuckoo DPS includes portions of the Rio Grande 
hydrological basin, and excludes the Pecos River drainage.
    The Rio Grande basin differs from the rest of the DPS in that it 
includes an area which drains to the Gulf of Mexico. However, its 
inclusion is consistent with the DPS in other respects. First, the DPS 
boundary follows the crest of the southeastern extent of the Rocky 
Mountains. This crest region encompasses a series of mountain ranges 
and other highlands above 1,800 m (6,000 feet), including the Sange de 
Cristo, Sandia, Manzano, San Andres, Sacramento, and Guadalupe 
mountains. In this region, the DPS boundary also includes as extensive 
desert basins, notable the Tularosa and Jornado del Muerto basins. 
Together, these highlands, mountains, and desert basins, centered on 
the ranges that divide the Pecos and Rio Grande rivers, form a broad 
zone that lacks suitable nesting habitat and is expected to separate 
the eastern and western cuckoo populations, as do the higher mountains 
along the crest farther north. Second, ecologically, the portion of the 
Rio Grande basin within the DPS has greater affinity with the western 
United States than with the area east of the Rocky Mountains (Graham 
1993; U.S. North American Bird Conservation Initiative (NABCI), in 
litt., 2000; Pashley et al. 2000), whereas regions east of the DPS 
(lower Rio Grande) have greater affinity for the Great Plains and other 
eastern ecological regions. The riparian habitats in the Rio Grande of 
New Mexico and west Texas are similar to those occupied by yellow-
billed cuckoos in other western regions, being dominated by Fremont 
cottonwood and willows, whereas most yellow-billed cuckoo habitat along 
the Pecos River in New Mexico historically lacked cottonwood forests, 
and today is dominated by non-native tamarisk trees, which have allowed 
an expansion of the cuckoo population along the Pecos River (W. Howe, 
pers. comm., 1999; Hunter et al. 1988; Ellis 1995). West Texas has been 
recognized by ecologists as part of a distinct ecological province or 
region, the Chihuahuan Desert, which is ecologically different from 
areas to the east which are not within the boundary of this DPS. In 
fact, the DPS boundary and Chihuahuan Desert boundary closely coincide 
in west Texas (e.g., see Chihuahuan Desert map at http://nasa.utep.edu/
chih/chihdes.htm). Third, as discussed elsewhere in this finding, 
cuckoos nesting along the Rio Grande of west Texas and New Mexico 
behave as do other western cuckoos in the timing of their spring 
migration, arriving on their breeding grounds at least 3-4 weeks later 
than their eastern counterparts (Bailey 1928; Bent 1940; Oberholser and 
Kincaid 1974; Hughes 1999; Sproul in litt 2000). For these reasons, the 
crest of the Rocky Mountains presents a clearer geographic and biologic 
separation in New Mexico and west Texas, than does the Continental 
    In general, the western Great Plains region lacks suitable habitat 
and contributes to the separation between eastern and western yellow-
billed cuckoos. However, the Great Plains are not a complete barrier to 
yellow-billed cuckoos because the species nests in riparian corridors 
that extend westward towards the Rocky Mountains along tributaries of 
the Mississippi and Missouri Rivers. These riparian corridors connect 
with extensive yellow-billed cuckoo habitat to the east that quite 
possibly support large yellow-billed cuckoo populations, notably in the 
bottomlands of the Mississippi River and its major tributaries. Thus, 
these corridors decrease the physical separation between yellow-billed 
cuckoos east and west of the Rocky Mountain crest. The effect of these 
corridors on gene flow and population interchange is unknown. Evidence 
from other bird species provide examples of boundaries between eastern 
and western taxa which meet and are maintained in the eastern Rocky 
Mountain-western Great Plains region (Gill 1989; Ehrlich et al. 1988). 
For example, the ranges of at least fourteen pairs of closely related 
eastern and western bird species meet in Great Plains, with minimal 
overlap between the species in most cases (Ehrlich et al. 1988). 
Although the yellow-billed cuckoo question does not involve separate 
species, this example suggests some underlying differences between 
eastern and western regions that may help maintain boundaries between 
species in the area of the Rocky Mountains-Great Plains.
    More relevant to the question of separation of yellow-billed cuckoo 
populations are bird species for which recognized eastern and western 
bird subspecies meet along a north-south boundary in the Rocky 
Mountain-western Great Plains region. These species include several 
which, like the yellow-billed cuckoo, migrate south to neotropical 
wintering areas: Bell's vireo (Vireo bellii) (AOU 1957; Sibley 2000), 
yellow warbler (Dendroica petechia), yellow-rumped warbler (D. 
coronata), and yellow-breasted chat (Icteria virens) (Dunn and Garrett 
1997). Of further interest and relevance to the question of 
separateness of western and eastern yellow-billed cuckoos is the 
evidence that eastern and western subspecies of several species of 
neotropical migrants winter in separate areas. These species include 
Bell's vireo (AOU 1957) and yellow warbler, orange-crowned warbler 
(Vermivora celata), Nashville warbler (V. ruficapilla), yellow-rumped 
warbler, Wilson's warbler, and yellow-breasted chat (Dunn and Garrett 
1997). These examples indicate that the Rocky Mountains-western Great 
Plains region does serve to separate populations of other neotropical 
migrant birds sufficiently to maintain measurable, subspecific 
    Little is known about the migratory paths of individual species or 
populations, but some evidence exists to support that eastern and 
western bird populations tend to follow different migratory paths. 
First, the primary migratory paths are north-south, parallel to the 
axis of the Rocky Mountains and most other western mountain ranges, and 
in general, bird migration in North America is primarily along four 
north-south routes or flyways (Pacific, Central, Mississippi, and 
Atlantic) (Ehrlich et al.

[[Page 38621]]

1988). Thus, eastern and western birds tend to follow distinct 
migration routes, with western (Pacific flyway) birds following 
different paths than Great Plains (Central Flyway) and eastern birds 
(Mississippi, Atlantic flyways). In addition, studies to date in Europe 
and North America indicate that migrating birds do respond to major 
topographic features such as mountain ranges (Walcott and Lednor 1983; 
Williams et al. 2001). We are not aware of migration route studies in 
the Rocky Mountains, but a recent study in the northern Appalachian 
Mountains found that southbound avian migrants oriented to topography 
(Williams et al. 2001). The authors of that study concluded that, as 
observed in the Alps of Europe, landforms have a significant guiding 
effect on migrating birds, with lower-flying birds tending to change 
course to fly parallel to mountain ridges, and to use passes when their 
migration route required crossing the axis of a range (Williams et al. 
    In our 90-day administrative finding for this petition (65 FR 
8104), we discussed the fact that the yellow-billed cuckoo is a mobile 
species, migrating to South America during the non-breeding season. 
This mobility raises the question of whether 240 km (150 mi) of 
mountains poses a barrier to movement between populations east and west 
of the crest of the Rocky Mountains. We are unaware of scientific data 
which would allow us to directly address the effectiveness of the 
mountains as a physical separation between yellow-billed cuckoo 
populations, but some evidence bears on the question. We have already 
described the observation that a broad area of unsuitable habitat 
largely separates suitable, occupied habitat east and west of the crest 
of the Rocky Mountains. Also, many other bird species migrate between 
Central/South America and North America and have maintained discrete 
populations or subspecies, which are separated by the Rocky Mountains 
(Pitelka 1947; Udvardy 1963; Johnsgard 1986).
    Data from movements of banded yellow-billed cuckoos provide no 
evidence of movement between eastern and western yellow-billed cuckoo 
populations, across the Rocky Mountain crest. Analyzing BBL banding 
data found that of a total of 8,673 banded yellow-billed cuckoos, of 
which 26 bands were recovered, no western birds were found east of the 
Rocky Mountain crest, nor eastern birds recovered west of the crest. 
While the data provide no evidence for movement between eastern and 
western yellow-billed cuckoo populations, the sample size is too small 
to adequately test the hypothesis that movement is limited between 
eastern and western regions. Only 251 yellow-billed cuckoos were banded 
in western States, with only one band recovery. Eight of the 26 
recovered birds were found in a State different from where it was 
banded. Of these, only one significant displacement occurred on an east 
to west axis, for a bird banded in Iowa and recovered in Pennsylvania.
    The extent to which yellow-billed cuckoos nesting in different 
regions of North America commingle during migration, or while 
overwintering, is unknown. Data provided by the BBL, from bird band 
returns to date is insufficient to determine migration or wintering 
patterns (BBL, in litt., 1998). While some scientists have provided 
information supporting the hypothesis that yellow-billed cuckoos 
breeding in the western United States winter in different regions of 
South America than do yellow-billed cuckoos nesting east of the Rocky 
Mountains (R. Ridgely, in. litt. 2000; J. Hughes in. litt. 2000; S. 
Laymon in. litt. 2000), the information available is not sufficient to 
test the hypothesis.
    Western yellow-billed cuckoos have historically occurred and/or 
still occur in several distinct ecoregions including the Great Basin, 
Sonoran Desert, Sonoran and Mohave Deserts, Northern Pacific 
Rainforest, Northern Rockies, Southern Rockies/Colorado Plateau, 
Coastal California, and Sierra Madre Occidental ecoregions (Graham 
1993; NABCI, in litt., 2000; Pashley et al. 2000). While these western 
ecoregions differ in many respects, they are joined by common factors, 
which also distinguish them from most eastern ecoregions within which 
yellow-billed cuckoos occur. Foremost among these is the fact that 
western yellow-billed cuckoo populations occur along narrow and patchy 
riparian corridors that provide suitable moist deciduous woodlands 
within otherwise unsuitable arid landscapes. By contrast, east of the 
Rocky Mountains, the yellow-billed cuckoo occurs in extensive 
bottomland forests in the Mississippi River and other drainages, as 
well in deciduous woodlands in non-riparian situations, including 
deciduous forests such as oak hickory forests, parks, and some suburban 
areas (Wilson 1999; Amundson et al., in litt., 2000).

Morphological, Physiological, Behavioral, and Genetic Discreteness

    Data collected from publications and other sources demonstrate, to 
varying degrees of certainty, the existence of morphological, 
physiological, and behavioral differences between eastern and western 
yellow-billed cuckoos.
    Based on the available information, the best evidence of 
behavioral/physiological differences between yellow-billed cuckoos 
populations west and east of the Rocky Mountain crest is differences in 
the timing of arrival during the spring migration, and the timing of 
nesting. Several authors have observed that western yellow-billed 
cuckoos arrive and nest substantially later than do eastern yellow-
billed cuckoos (Hughes 1999; Franzreb and Laymon 1993; S. Laymon in. 
litt. 2000), while an Arizona study found less of a pattern, but noted 
that Arizona yellow-billed cuckoos appeared to nest several weeks later 
than California yellow-billed cuckoos (Hamilton and Hamilton 1965). 
Franzreb and Laymon (1993) and Hughes (1999) concluded that the nesting 
season in western States begins a full three to four weeks later than 
it does east of the Rocky Mountains, and that western yellow-billed 
cuckoos arrive on their breeding grounds 4 to 8 weeks later than do 
eastern yellow-billed cuckoos at similar latitudes. One scientist has 
also suggested that the breeding season of western birds is shorter 
than for eastern birds, due to later spring arrival and earlier fall 
departure, and that is evidence of evolved behavioral differences 
between eastern and western yellow-billed cuckoos (Hughes, in. litt. to 
K. Suckling, 2000).
    We compared the timing of arrival on breeding grounds from several 
studies and concluded that there is at least a 3 to 4 week difference 
in the peak of migration and onset of nesting season, with eastern 
yellow-billed cuckoos being the earliest (Chapman 1903; Bent 1940; 
Franzreb and Laymon 1993; Hughes 1999; S. Laymon, in litt., 2000). In 
our 90-day finding for this petition (65 FR 8104), we speculated that 
differences in timing of arrival on breeding grounds and in breeding 
could be the result of genetically-similar birds responding to local 
environmental cues. We believe this remains as one hypothesis for 
timing of breeding (Hamilton and Hamilton 1965), although the 
difference could also reflect genetic-based differences. In the case of 
timing of arrival on breeding grounds, comments received in response to 
the 90-day finding (S. Laymon in. litt., 2000; J. Hughes in. litt. to 
K. Suckling, 2000; Amundson et al., in litt., 2000) provide a 
persuasive argument that timing of arrival is more likely the result of 
an evolved response to east-west differences, via mechanisms likely 
under genetic control.
    Other differences between yellow-billed cuckoos in the proposed 
western DPS and eastern yellow-billed cuckoos

[[Page 38622]]

exist and provide additional evidence of discreteness. For example, 
western yellow-billed cuckoos have larger egg size and weight (mass in 
grams), with thicker egg shells than the eastern yellow-billed cuckoo 
(Hughes 1999). This difference may correlate with potential higher egg 
water loss from hotter, dryer conditions in the west than the east 
(Hamilton and Hamilton 1965; Ar et al. 1974; Rahn and Ar 1974).
    Eastern juveniles have been reported to have yellow bills 
(Oberholser and Kincaid 1974), while western juveniles in California 
are reported to have all-black bills (Franzreb and Laymon 1993). 
However, since bill color in juveniles changes from grayish, to yellow 
and black around the age of 60 days (Hughes 1999), this reported 
difference needs to be verified, taking into account juvenile age.
    Western adult yellow-billed cuckoos have been reported to have an 
orange lower mandible, while eastern adults have a yellow lower 
mandible (Franzreb and Laymon 1993; S. Laymon, in. litt. 2000). No 
scientific data are available to verify this, and the reported 
difference has not been the subject of a published scientific study. 
However, Dr. Stephen Laymon has worked extensively with western yellow-
billed cuckoos and is a species expert.
    Western adults, on average, are larger and heavier than eastern 
adult birds. These differences are discussed above and in the 
literature (Banks 1988, 1990; Franzreb and Laymon 1993; Oberholser and 
Kincaid 1974), and are evidence of some degree of physical isolation. 
However, as discussed by Banks (1988, 1990), and in our 90-day 
administrative finding, the differences are not strong, and may be 
clinal. We believe that these differences merit further analysis, with 
greater sample sizes and using a greater number of morphological 
    From the analysis of two different mtDNA genes (control region and 
ATP8) totaling 736 base pair sequences, Dr. Fleischer concluded that 
there was significant divergence in haplotype (set of genes that 
determine different antigens) frequencies between eastern and western 
samples, which suggests that they may not currently be exchanging many 
migrants (Fleischer 2001).
    In view of the above information, we find that the available 
information supports the recognition of a western DPS of the yellow-
billed cuckoo, as described, based on the physical, ecological, and 
behavioral discreteness of the population segment.


    Under our DPS policy, once we have determined that a population 
segment is discrete, we consider its biological and ecological 
significance to the larger taxon to which it belongs. This 
consideration may include, but is not limited to, evidence of the 
persistence of the discrete population segment in an ecological setting 
that is unique for the taxon; evidence that loss of the population 
segment would result in a significant gap in the range of the taxon; 
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 its historic range; and evidence that the 
discrete population segment differs markedly from other populations of 
the species in its genetic characteristics. Significance is not 
determined by a quantitative analysis, but instead is a qualitative 
finding. It will vary from species to species and cannot be reduced to 
a simple formula or flat percentage. We have found substantial evidence 
that three of these significance factors are met by the discrete 
population segment of yellow-billed cuckoos that occurs west of the 
Rocky Mountain crest.
    Loss of the western yellow-billed cuckoo population segment would 
result in loss of the species from the United States west of the 
continental divide and the Rocky Mountain crest. This represents a loss 
of the species from about 28 percent of its historic range in the 
continental United States. If one assumes that the species is already 
extirpated from the States of Washington and Oregon, the loss would 
still exceed more than 20 percent of the species' current range, and 
recent records indicate that the species may still persist in small 
numbers in eastern Oregon. Because the proportion of the total suitable 
yellow-billed cuckoo habitat in the west is lower than the proportion 
of the range (because the cuckoo uses more narrowly circumscribed 
habitat types in the west than the east), we do not believe that loss 
of the species from the west would by itself require listing the 
species as a whole; however, we emphasize that the ``significant gap in 
the range'' analysis required for a DPS is different than the 
``significant portion of the range'' analysis required for a listing 
decision for the entire species. We believe that loss of the species 
from the United States west of the continental divide and the Rocky 
Mountain crest would result in a significant gap in the range of the 
species as a whole.
    We discussed above the manners in which the ecological setting used 
by western yellow-billed cuckoos differs fundamentally from that of 
eastern yellow-billed cuckoos, because of the western population 
segment's strong association with non-montane riparian woodlands, 
contrasting sharply with States east of the Rocky Mountains, where 
yellow-billed cuckoos nest across a much broader range of habitat 
conditions. In the western States, the yellow-billed cuckoo occurs 
primarily in arid regions where riparian woodlands, particularly those 
which include cottonwood trees as a dominant component, provide 
ecological conditions which are unique for the region. These conditions 
are essential to the survival of yellow-billed cuckoo in the west, as 
well as to the survival of many other riparian-dependent species 
(Hunter et al. 1987; Sanders and Edge 1998; Knopf and Samson 1994).
    The western yellow-billed cuckoo populations have persisted over 
long periods, despite the small number of breeding pairs which breed in 
relatively isolated areas. Although site fidelity and dispersal 
patterns have not been studied, a limited number of banding returns 
from the yellow-billed cuckoo population on the South Fork Kern River 
in California indicate that adult birds return to the same nesting 
areas in subsequent years (S. Laymon, in litt., 2000). Although the 
species is reported to have nomadic tendencies (Hughes 1999), the 
repeated return from South America each spring to relatively isolated 
breeding sites is strongly suggestive of site fidelity. A scenario of 
strong breeding site fidelity, and often isolated breeding populations, 
combined with most river reaches supporting very few (less than 20) 
breeding pairs, suggests that local western populations may constitute 
important isolated units. Under this same scenario, these units may 
contain important genetic and phenotypic diversity.
    While recent analysis of the genetic differences between the 
eastern and western population segments of yellow-billed cuckoos 
(Fleischer 2001) indicates that these differences may not rise to the 
level typical of different subspecies, they do suggest that eastern and 
western populations are not now exchanging many migrants. Furthermore, 
analysis of the pattern of variation suggests that yellow-billed 
cuckoos may have recently (since the last glacial retreat) spread from 
a refugial population, released by habitat changes as the climate in 
North America warmed (Fleischer 2001). We believe that the existing 
western discrete

[[Page 38623]]

population segment of yellow-billed cuckoos may represent an early 
stage of evolutionary differentiation. Loss of this discrete population 
segment would result in the loss of genetic differences from eastern 


    We have evaluated as a DPS the population of western yellow-billed 
cuckoos from the portion of the United States west of the Rocky 
Mountain crest, addressing the two elements which our policy requires 
us to consider in deciding whether a vertebrate population may be 
recognized as a DPS and considered for listing under the Act. In 
assessing the population segment's discreteness from the remainder of 
the taxon, we have described the physical separation, ecological 
discreteness, behavioral discreteness as reflected in the timing of 
migration and nesting, and morphologic data. We considered 
distributional data, ecological, behavioral, morphologic and genetic 
information, information from banding returns, and geographic and 
biogeographic patterns and have concluded that this population segment 
is discrete under our DPS policy. In assessing the population segment's 
significance to the taxon to which it belongs, we have considered the 
available information, including the large geographic area represented 
by the western DPS, its ecological distinctness, which is typified by 
cottonwood-willow riparian woodlands upon which the western DPS largely 
depends for breeding, its genetic differences from other cuckoo 
populations in the eastern United States, and other considerations and 
factors discussed above. We have concluded that loss of the species 
from the portion of the United States west of the Rocky Mountain crest 
would represent a significant gap in the species' range, the loss of 
the species from a unique ecological setting, and the loss of genetic 
differences from eastern yellow-billed cuckoos. Therefore, as the 
population segment meets both the discreteness and significance 
criteria of our DPS policy, the DPS qualifies for consideration for 
listing. An evaluation of the level of threat to the DPS based on the 
five listing factors established by the Act to determine if listing of 
the DPS follows.

Summary of Factors Affecting the DPS

    Section 4 of the Act and regulations (50 CFR part 424) promulgated 
to implement the listing provisions of the Act describes the procedures 
for adding species to the Federal lists. A species may be determined to 
be an endangered or threatened species due to one or more of the five 
factors described in section 4(a)(1). These factors, and their 
application to the yellow-billed cuckoo, are as follows:
    A. The present or threatened destruction, modification, or 
curtailment of its habitat or range. Principal causes of riparian 
habitat losses are conversion to agricultural and other uses, dams and 
river flow management, stream channelization and stabilization, and 
livestock grazing. Available breeding habitats for yellow-billed 
cuckoos have also been substantially reduced in area and quality by 
groundwater pumping, and the replacement of native riparian habitats by 
invasive non-native plants, particularly tamarisk (Groschupf 1987; 
Rosenberg et al. 1991). Estimates of riparian habitat losses include 
90-95 percent for Arizona, 90 percent for New Mexico, 90-99 percent for 
California, and more than 70 percent nationwide (Noss et al. 1995; 
Ohmart 1994). Much of the remaining habitat is in poor condition and 
heavily affected by human use (U.S. Department of Interior 1994; Almand 
and Krohn 1978). Fragmentation effects include the loss of patches 
large enough to sustain local populations, leading to local 
extinctions, and the potential loss of migratory corridors, affecting 
the ability to recolonize habitat patches (Hunter 1996).
    Dahl (1990) reviewed estimated losses of wetlands between 1780 and 
the 1980s in the Southwest: California is estimated to have lost 91 
percent, Nevada 52 percent, Utah 30 percent, Arizona 36 percent, New 
Mexico 33 percent, and Texas 52 percent. As much as 90 percent of major 
lowland riparian habitat has been lost or modified in Arizona (State of 
Arizona 1990). Franzreb (1987) noted that ``(B)ottomland riparian 
forests are the most highly modified of natural landscapes in 
    Much of the dramatic decline of the yellow-billed cuckoo in 
California has been directly attributed to breeding habitat loss from 
clearing and removal of riparian forest for agriculture, urban 
development and flood control (Gaines 1974; Gaines and Laymon 1984; 
Laymon and Halterman 1987b; Launer et al. 1990; Hughes 1999). Losses in 
the Central Valley alone have been relatively large, especially along 
the Valley's formerly free-flowing rivers such as the Sacramento where, 
under pristine conditions, broad overflow plains and dense riparian 
forests extended for up to 8 km (5 mi) from both banks (Service 2000). 
Following the most intense reclamation and development period, Kabitah 
(1984) estimated that Central Valley riparian forests had been reduced 
by more than 95 percent from historical condition and that a large 
proportion of remaining forests were in highly disturbed or degraded 
condition. A recent study of the San Joaquin River between Friant Dam 
and Merced River confluence found that between 1937 and 1993, the area 
of riparian forest and scrub decreased 28 percent, from 2,745 to 1,989 
ha (6,787 to 4,914 ac) (Jones & Stokes Associates, Inc. 1998).
    Suitable habitat for the yellow-billed cuckoo is very limited in 
Nevada with most areas of cottonwood riparian forests being fragmented 
(NDW, in litt., 2001). Studies from Great Basin National Park (NPS, in 
litt., 2001) in the South Snake Mountain Range determined that of the 
190 ha (469 ac) of existing riparian habitat only 3 ha (8 ac) was 
suitable for supporting yellow-billed cuckoo. Most of the suitable 
habitat along the Truckee, Carson, and Walker Rivers has been modified 
or destroyed (NDW, in litt., 1985, 1990).
    Loss and modification of southwestern riparian habitats have 
occurred from urban and agricultural development, water diversion and 
impoundment, channelization, livestock grazing, off-road vehicle and 
other recreational uses, and hydrological changes resulting from these 
and other land uses. Rosenberg et al. (1991) noted that ``it is the 
cottonwood-willow plant community that has declined most with modern 
river management.'' Loss of the cottonwood-willow riparian forests has 
had widespread impact on the distribution and abundance of bird species 
associated with that forest type (Hunter et al. 1987; Hunter et al. 
1988; Rosenberg et al. 1991).
    Overuse by livestock has been a major factor in the degradation and 
modification of riparian habitats in the western United States. The 
effects include changes in plant community structure and species 
composition, and relative abundance of species and plant density. These 
changes are often linked to more widespread changes in watershed 
hydrology (Rea 1983; General Accounting Office (GAO) 1988). Livestock 
grazing in riparian habitats typically results in reduction of plant 
species diversity and density, especially of palatable broadleaf plants 
like willows and cottonwood saplings, and is one of the most common 
causes of riparian degradation (Carothers 1977; Rickard and Cushing 
1982; Cannon and Knopf 1984; Klebenow and Oakleaf 1984; GAO 1988; Clary 
and Webster 1989; Schultz and Leininger 1990).
    Increases in abundance of riparian bird species have followed 

[[Page 38624]]

modification, or removal of cattle grazing. Krueper (1993) found the 
following increases in birds associated with cottonwood-willow habitat 
on Arizona's San Pedro River 4 years after the removal of livestock: 
yellow warbler, 606 percent; common yellow-throat, 2,128 percent; 
yellow-breasted chat, 423 percent. Bock et al. (1993) found that 40 
percent of the riparian bird species they examined were negatively 
affected by livestock grazing. As shady, cool, wet areas providing 
abundant forage, they are disproportionately preferred by livestock 
over the surrounding xeric uplands (Ames 1977; Valentine et al. 1988; 
A. Johnson 1989). Harris et al. (1986) believed that termination of 
grazing along portions of the South Fork of the Kern River in 
California was responsible for increases in riparian vegetation.
    Another likely factor in the loss and modification of the habitat 
for yellow-billed cuckoo is the invasion by the non-native tamarisk. 
Tamarisk was introduced into western North America from the Middle East 
in the late 1800s as an ornamental windbreak and for erosion control. 
It has spread rapidly along southwestern watercourses, typically at the 
expense of native riparian vegetation, especially cottonwood/willow 
communities. Although tamarisk is present in nearly every southwestern 
riparian community, its dominance varies. It has replaced some 
communities entirely, but occurs at a low frequency in others.
    The spread and persistence of tamarisk has resulted in significant 
changes in riparian plant communities. In monotypic tamarisk stands, 
the most striking change is the loss of community structure and 
diversity. The multilayered community of herbaceous understory, small 
shrubs, middle-layer willows, and overstory deciduous trees is often 
replaced by one monotonous layer. Plant species diversity has declined 
in many areas, and relative species abundance has shifted in others. 
Other effects include changes in percent cover, total biomass, fire 
cycles, thermal regimes, and perhaps insect fauna (Kerpez and Smith 
1987; Carothers and Brown 1991; Rosenberg et al. 1991; Busch and Smith 
    Disturbance regimes imposed by man (e.g., grazing, water diversion, 
flood control, woodcutting, and vegetation clearing) have facilitated 
the spread of tamarisk (Behle and Higgins 1959; Kerpez and Smith 1987; 
Hunter et al. 1988; Rosenberg et al. 1991). Cattle find tamarisk 
unpalatable. However, they eat the shoots and seedlings of cottonwood 
and willow, acting as a selective agent to shift the relative abundance 
of these species (Kerpez and Smith 1987). Degradation and, in some 
cases, loss of native riparian vegetation lowered the water table and 
has resulted in the loss of perennial flows in some streams. With its 
deep root system and adaptive reproductive strategy, tamarisk thrives 
or persists where surface flow has been reduced or lost. Further, 
tamarisk establishment often results in a self-perpetuating regime of 
periodic fires, which were uncommon in native riparian woodlands (Busch 
and Smith 1993).
    Manipulation of perennial rivers and streams has resulted in 
habitats that tend to allow tamarisk to out-compete native vegetation. 
Construction of dams created impoundments that destroyed native 
riparian communities. Dams also eliminated or changed flood regimes, 
which were essential in maintaining native riparian ecosystems (Vogl 
1980; Richter and Richter 2000). Changing (usually eliminating) flood 
regimes provided a competitive edge to tamarisk. In contrast to native, 
deep-rooted species, tamarisk does not need floods and is intolerant of 
submersion when young. Diversion of water caused the lowering of near-
surface groundwater and reduced the relative success of native species 
in becoming established. Irrigation water containing high levels of 
dissolved salts also favors tamarisk, which is more tolerant of high 
salt levels than most native species (Kerpez and Smith 1987; Busch and 
Smith 1993).
    Conversion to tamarisk typically coincides with reduction or 
complete loss of bird species strongly associated with cottonwood-
willow habitat, including the yellow-billed cuckoo (Hunter et al. 1987; 
Hunter et al. 1988; Rosenberg et al. 1991). While Brown and Trosset 
(1989) believed tamarisk may serve as an ``ecological equivalent'' to 
native vegetation, they noted that their study occurred where a 
tamarisk community became established where no native equivalent 
existed before. This is especially evident along the Pecos River in 
Texas (Hunter et al. 1988).
    Water developments also likely reduced and modified yellow-billed 
cuckoo habitat. The series of dams along most major southwestern rivers 
(Colorado, Gila, Salt, Verde, Rio Grande, Kern, San Diego, and Mojave) 
have altered riparian habitats downstream of dams through hydrological 
changes, vegetational changes, and inundated habitats upstream. New 
habitat is sometimes created along the shoreline of reservoirs, but 
this habitat (often tamarisk) is often unstable because of fluctuating 
levels of regulated reservoirs (Grinnell 1914; Phillips et al. 1964; 
Rosenberg et al. 1991).
    Diversion and channelization of natural watercourses are also 
likely to have reduced yellow-billed cuckoo habitat. Diversion results 
in diminished surface flows and increased salinity of residual flows. 
Consequent reductions and composition changes in riparian vegetation 
are likely. Channelization often alters stream banks and fluvial 
dynamics necessary to maintain native riparian vegetation (Vogl 1980; 
Richter and Richter 2000).
    River channelization, construction of levees close to the river, 
and riprap along the levees have fragmented riparian habitat along the 
Sacramento River and disrupted the ecological processes which both 
renew and restore riparian and aquatic habitats (Laymon and Halterman 
1987a; Halterman 1991; Service 2000). More than one-half of the 
Sacramento River's banks within the lowermost 312 km (194 mi) of river 
have been riprapped over the last four decades (Service 2000). The 
result is that much of the River's remaining riparian habitat now 
occurs in the form of narrow disconnected linear patches (Service 2000; 
Halterman et al. 2001), unsuitable for yellow-billed cuckoo nesting 
(Gaines 1974). This may be due to the loss of continuous migration 
corridors, lack of patches of adequate size for nesting, and the 
species' inability to use highly isolated patches (Halterman 1991). 
Exacerbating such problems is the fact that the yellow-billed cuckoo 
now, for unknown reasons, utilizes a narrower range of habitats in 
California, now predominantly cottonwood-willow complex, than it did 
historically (Laymon and Halterman 1987b).
    The yellow-billed cuckoo is considered very vulnerable from 
deforestation of its wintering grounds (Morton 1992), and while losses 
of neotropical forests and woodlands have been substantial and ongoing, 
particularly in Central America and northern South America (Hartshorn 
1992; Brown and Lomolino 1998), the relationship between overwintering 
habitat and yellow-billed cuckoo populations has not been studied or 
    B. Over-utilization for commercial, recreational, scientific, or 
educational purposes. We are unaware of threats resulting from 
    C. Disease or predation. We are unaware of any disease or predation 
that constitutes a significant threat to yellow-billed cuckoos. 
However, adults have been preyed upon by falcons (Hector 1985; Bob 
Altman, North American Bird Conservation Initiative,

[[Page 38625]]

Northern Pacific Rain Forests Region, Oregon, pers. comm., 2001), and 
nestlings have been taken by hawks, jays, grackles (Launer et al. 1990; 
Nolan and Thompson 1975), and by various snake and mammal species 
(Nolan 1963). In eastern Mexico, adults are frequently attacked by 
raptors during migration (J.K. Wilson, pers. comm., in Hughes 1999; 
Wilson 1999). In a recent study of 252 yellow-billed cuckoo nests in 
Arkansas, predation accounted for 91 percent of all nest failures, with 
small mammals, birds, and reptiles depredating the greatest proportion 
(Wilson 1999).
    D. The inadequacy of existing regulatory mechanisms. The Migratory 
Bird Treaty Act (MBTA) (16 U.S.C. Sec. 703-712) is the only current 
Federal protection provided the yellow-billed cuckoo. The MBTA 
prohibits ``take'' of any migratory bird, which is defined as: ``* * *  
to pursue, hunt, shoot, wound, kill, trap, capture, or collect, or 
attempt to pursue, hunt, shoot, wound, kill, trap, capture, or collect 
* * * .'' However, unlike the Endangered Species Act, there are no 
provisions in the MBTA preventing habitat destruction unless direct 
mortality or destruction of active nests occurs.
    The majority of the occupied areas west of the Continental Divide 
for the yellow-billed cuckoo lies within California, Arizona, and New 
Mexico (Hughes 1999). Only California classifies the yellow-billed 
cuckoo as endangered (California Department of Fish and Game (CDFG) 
2001). In Arizona, the species was formerly State-listed as threatened, 
but is now considered a Wildlife of Concern, a designation which the 
Arizona Game and Fish Department now uses for wildlife instead of 
``threatened''. Neither its past status as threatened nor its current 
status as a species of concern confers any protection to the species in 
Arizona. The bird has no special protective status in Wyoming, New 
Mexico, Colorado, Idaho, or Texas (Groschupf 1987), and habitat 
protection or protection of individuals is not provided beyond existing 
regulations on capture, handling, transportation, and take of native 
wildlife. Utah considers the yellow-billed cuckoo as threatened. In 
Nevada, the yellow-billed cuckoo is identified as critically imperiled 
due to extreme rarity, imminent threats, or biological factors, and is 
proposed for protection as threatened. The California Endangered 
Species Act (CESA) prohibits unpermitted possession, purchase, sale, or 
take of listed species. However, the CESA definition of take does not 
include harm, which under the Act can include destruction of habitat 
that actually kills or injures wildlife by significantly impairing 
essential behavioral patterns (50 CFR 17.3). CESA does require 
consultation between the CDFG and other State agencies to ensure that 
activities of State agencies will not jeopardize the continued 
existence of State-listed species (CERES, in litt., 2001). Yellow-
billed cuckoos have no State status in Oregon because it has not been 
considered an active breeding species since the 1940s (B. Alterman, 
pers. comm., 2001). In Washington, the yellow-billed cuckoo is 
considered critically imperiled (five or fewer occurrences). However, 
no active nesting has been documented since the 1930s. We believe that 
these, and other regulatory mechanisms, are inadequate to ensure the 
continued existence of the western DPS of yellow-billed cuckoo.
    E. Other natural or human caused factors affecting the DPS' 
continued existence. Environmental, demographic, and genetic 
vulnerability to random extinction are recognized as interacting 
factors that might contribute to a population's extinction (Hunter 
1996). The riparian habitat on which the yellow-billed cuckoo depends 
has been reduced and degraded throughout the western continental U.S. 
Its habitat rarity and small, isolated populations make the remaining 
yellow-billed cuckoo populations in this region increasingly 
susceptible to local extirpation through stochastic events such as 
floods, fire, predation, depredation, and land development.
    Brood parasitism by the brown-headed cowbird (Molothrus ater) has 
been documented only six times (Wilson, in litt., 1999; Friedmann 
1971), and less so by the bronzed cowbird (Molothrus aeneus) 
(Clotfelter and Brush 1995). With an incubation period of 10-13 days, 
and fledging in 10-11 days, the brown-headed cowbird requires more 
development time before fledging than the yellow-billed cuckoo. 
Therefore, successful parasitism of yellow-billed cuckoo nest by brown-
headed cowbird is unlikely (Ehrlich et al. 1988).
    In addition to destruction and degradation of riparian habitats, 
pesticides may affect yellow-billed cuckoo populations (Groschupf 1987; 
Hughes 1999). Although the evidence is too limited to evaluate this 
effect, it warrants further study. In areas where riparian habitat 
borders agricultural lands, such as in California's Central Valley, 
pesticide use may affect yellow-billed cuckoos indirectly by reducing 
prey numbers, or directly by poisoning nestlings if sprayed in areas 
where the birds are nesting (Laymon and Halterman 1987b).
    Accumulation of chlorinated hydrocarbon pesticides, particularly 
DDT, has affected other bird species, particularly top predators 
(Robinson and Bolen 1989). Although DDT use has been banned in the 
United States since 1972, yellow-billed cuckoos may be exposed to DDT 
on wintering grounds where DDT use has not been banned. Analysis of two 
eggs collected in California in 1979 showed very low levels of DDE, a 
stable metabolite of DDT, but eggshell fragments collected in 1985 from 
three nests along the South Fork of the Kern River in California 
averaged 19 percent thinner than pre-DDT era eggshells (Laymon and 
Halterman 1987b). DDT has caused eggshell thinning in other bird 
species, but its role in the Kern River observations is unknown.


    We have carefully assessed the best scientific and commercial 
information available regarding the past, present, and future threats 
faced by this species. We reviewed the petition, information available 
in our files, other published and unpublished information submitted to 
us during the public comment period following our 90-day petition 
finding, consulted with recognized yellow-billed cuckoo experts, avian 
molecular geneticists, and other Federal, State, and Tribal resource 
agencies throughout the country. On the basis of the best scientific 
and commercial information available, we find that listing the yellow-
billed cuckoo western DPS as threatened is warranted, but precluded by 
higher priority listing actions.
    In making this finding, we recognize that there have been declines 
in the distribution and abundance of yellow-billed cuckoos throughout 
the western States, primarily attributed to habitat loss, degradation 
and fragmentation, overgrazing, replacement of native riparian woodland 
species by tamarisk and other non-native plants, and river management, 
including altered flow and sediment regimes, and flood control 
practices, such as channelization and bank protection.
    We conclude that the overall magnitude of threats to the western 
yellow-billed cuckoo DPS is high, and that the overall immediacy of 
these threats is non-imminent. Pursuant to our Listing Priority 
Guidance (64 FR 7114), a DPS for which threats are high but non-
imminent is assigned a Listing Priority Number of 6. While we conclude 
that listing the western DPS of the yellow-billed cuckoo is warranted, 
an immediate proposal to list is precluded by other higher priority 
listing actions. During this fiscal year,

[[Page 38626]]

2001, we must spend nearly all of our Listing Program funding to comply 
with court orders and judicially approved settlement agreements, which 
are now our highest priority actions. The western DPS of the yellow-
billed cuckoo will be added to the list of candidate species upon 
publication of this notice of 12-month finding. We will continue to 
monitor the status of this species and other candidate species. Should 
an emergency situation develop with one or more of the species, we will 
act to provide immediate protection, if warranted.
    We intend that any proposed listing action for the yellow-billed 
cuckoo western DPS will be as accurate as possible. Therefore, we will 
continue to accept additional information and comments from all 
concerned governmental agencies, the scientific community, industry, or 
any other interested party concerning this finding. Before we proceed 
with listing the yellow-billed cuckoo we will solicit a scientific peer 
review of the DPS boundary.

References Cited

    A complete list of references cited herein, as well as others, is 
available upon request from the Sacramento Fish and Wildlife office 
(see ADDRESSES section).


    This document was prepared by the Sacramento Fish and Wildlife 
Office (see ADDRESSES section).


    The authority for this action is the Endangered Species Act of 
1973, as amended (16 U.S.C. 1531 et seq.).

    Dated: July 18, 2001.
Marshall P. Jones, Jr.,
Acting Director, U.S. Fish and Wildlife Service.
[FR Doc. 01-18560 Filed 7-24-01; 8:45 am]