Contaminants and Birds
Monitoring Contaminants in Arctic and American Peregrine
Falcons in Alaska
Arctic and American peregrine falcons (Falco peregrinus tundrius
and F. p. anatum) were listed as endangered under the Endangered
Species Preservation Act (1969) in 1970, and later, in 1973,
under the Endangered Species Act. At the time of listing,
some local populations of American peregrine falcons in the
eastern United States had disappeared, and populations in
western and northern North America had been reduced by 80
percent or more. Organochlorine pesticides such as DDT and
its breakdown product DDE were identified as the cause of
the decline. The peregrines accumulated these chemicals in
their tissues by feeding on birds that had eaten DDT-contaminated
insects or seeds. These chemicals prevented normal calcium
deposition during eggshell formation, and caused females to
lay thin-shelled eggs that often broke before hatching. The
use of DDT was restricted in the United States and Canada
in the early 1970s, and by the late 1970s, populations of
peregrine falcons were beginning to recover.
After Arctic and
American peregrine falcons were listed, recovery plans
for four different geographic areas were prepared.
For the Alaska populations, the Recovery Plan identified
specific "index" areas (areas representative of interior
and northern Alaska) to survey, and specific recovery criteria
to be achieved prior to reclassification. These criteria
included number of pairs occupying territories, number
of young produced,
amount of DDE residue in eggs, and eggshell thickness for
each of the index areas.
In the early 1980s, biologists in Region 7's Endangered Species
and Contaminant Divisions initiated a contaminant monitoring
program for peregrine falcons in Alaska. This program has
continued throughout the 1990s. The monitoring plan focused
on DDE and eggshell thinning, as identified in the Recovery
Plan, and called for collecting and analyzing a minimum of
10 eggs from each subspecies every five years. Unhatched eggs
were also collected when visiting nests to color band falcons
for mortality and movement studies. We began the program in
1984, and repeated the effort in 1989 and 1995. During this
monitoring effort, 153 eggs were collected, 87 from American
peregrine falcons and 66 from arctic peregrine falcons.
Analysis of eggs collected during these three periods showed
a clear downward trend of DDE concentrations in eggs. In the
late 1960s, DDE residues in the range of 20-40 ppm (parts
per million) and eggshell thinning in excess of 20 percent
were observed for peregrine falcons in Alaska (Peakall et.
al 1975). Peakall (1976) reported that DDE residues in eggs
in the range of 15 to 20 ppm would likely result in a declining
peregrine falcon population. By 1995, DDE levels had declined
to 2 to 3 ppm. Eggshell thickness also increased following
the 1972 restrictions on DDT, although this increase appears
to have leveled off at about 10 to 12 percent thinner than
pre-DDT levels. Although current egg shells are still thinner
than pre-DDT levels, reproductive success has been good. We
are unsure why, with continuing declines in DDE, egg shell
thickness has not continued to improve. We will continue to
investigate other possible causes, including other contaminants.
During this monitoring effort, we were able to gain insight
into other specific aspects of contaminants: four banded females
were sampled twice during the study period, which provided
insight on how residue levels in specific individuals change
over time; and 15 adult females, whose age was known because
they were color-banded as young, were sampled once. In addition,
in the early 1990s, a migration study using satellite telemetry
was undertaken and some of these tagged birds (four females),
with known wintering locations, were sampled. While DDE residues
varied among winter locations, none of the residue levels
of eggs from these four females were particularly high.
monitoring program in Region 7 has been one of the most
thorough ever, even for a species as well studied
as the peregrine falcon. With data collected during this
program, we were able to monitor the major threat to this
and we were able to base our reclassification decisions (delisting
of the Arctic peregrine falcon and the American peregrine
falcon) on very detailed and scientifically credible data.
As the FWS considers implementing post-delisting monitoring
plans, we will be developing a contaminant monitoring program
similar to the one we conducted in Alaska for lower 48
States' peregrine populations.
Skip Ambrose, Northern
Alaska Field Office, Fairbanks, Alaska
Peakall, D. B. 1976. The peregrine falcon (Falco peregrinus)
and pesticides. Canadian Field Naturalist 90:301-307.
Peakall, D. B., T. J. Cade, C. M. White, and J. R. Haugh.
1975. Organochlorine residues in Alaskan peregrines. Pesticide
Monitoring Journal 8:255-260.