Relationship of Diets and Environmental Contaminants in Wintering Bald Eagles

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Abstract
We investigated the relationship between diets and potential hazards in contaminants of wintering bald eagles, (Haliaeetus leucocephalus) in the Klamath Basin of northern California [USA] and southern Oregon. We studied diets by identifying remains of 913 prey items found at perches, examining 341 castings collected from communal night roosts, and observing foraging eagles. We determined residues of organochlorine compounds, lead (Pb), and mercury (Hg) in bald eagles and their prey by analzying eagle blood samples and carcasses and 8 major prey species. Bald eagles fed largely on waterfowl by scavenging cholera-killed ducks and geese and on microtine rodents during mid- to late winter. Residues of organochlorine pesticides and Hg in prey were low, and polychlorinated biphenyls (PCB''s) were detected in low concentrations in 9% of prey samples. Mean Pb concentrations in prey concentrations in prey ranged from 0.15 to 4.79 ppm. Mercury was detected in all eagle blood samples, and Pb was detected in 41% of the bald eagle samples. Mean Pb concentration in livers of dead eagles was 2.09 ppm and ranged as high as 27 ppm in an eagle that died of Pb poisoning. Prey of the eagles were relatively free of contaminants with the possible exception of embedded Pb slot in waterfowl, which may present a potential for Pb poisoning of eagles.