Productivity, diets, and environmental contaminants in nesting bald eaglesfrom the Aleutian Archipelago

We studied productivity, diets, and environmental contaminants in nesting b ald eagles from the western Aleutian Islands, Alaska, USA, during the summe rs of 1993 and 1994. Productivity on Adak, Tanaga, and Amchitka Islands ran ged from 0.88 to 1.24 young produced per occupied site and was comparable t o that of healthy populations in the lower 48 United States. However, produ ctivity on Kiska Island was depressed, averaging 0.67 young per occupied si te. The lower reproductive success on Kiska was associated with elevated le vels of dichlorodiphenyldichloroethylene and other organochlorine pesticide s. Many of the organochlorine pesticides were elevated in bald eagle eggs f rom the four islands, but concentrations of these contaminants and Hg were significantly higher in eggs from Kiska Island than in eggs from the other islands. In contrast, polychlorinated biphenyl concentrations were higher i n eggs from Adak, Amchitka, and Kiska (where military facilities have been installed) than in those from Tanaga (which has had little military activit y). The most likely source of these contaminants in bald eagles was from th eir diets, which were variable spatially and temporally. Fish made up most (56%) of the eagles' diet on Adak and Tanaga Islands, followed by birds (25 %) and mammals (19%). In contrast, birds comprised the majority (60%) of ba ld eagle diets on Amchitka and Kiska Islands, followed by mammals (30%) and fish (10%). The high proportion of seabirds in the diet of eagles from Kis ka Island could be the major source of organochlorine and Hg contamination. Elevated concentrations of organochlorines in bald eagle eggs from the Ale utian Archipelago was surprising, because of the distance to agricultural a reas. The results indicate that these contaminants can be transported long distances and affect wildlife populations in remote and pristine areas. We also discuss potential sources and transport mechanisms of these contaminan ts to the Aleutian Islands.