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 that needed 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.

Our contaminant 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 species (DDT), 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.

Last updated: February 13, 2013