|Environmental Contaminants in Bald Eagles Nesting in Hood Canal|
The bald eagle (Haliaeetus leucocephalus) is currently listed as a federally threatened species in Washington. In July 1999, the U.S. Fish and Wildlife Service published a proposal to delist the bald eagle under the Endangered Species Act. At the time the species was listed, environmental contaminants were cited as the primary reason for its decline. Beginning in the 1940's, dichloro diphenyl trichloroethane (DDT) and other organochlorine pesticides became widely used as insecticides. In the late 1960's and early 1970's, it was determined that dichlorophenyl-dichloroethylene (DDE), the principal breakdown product of DDT, accumulated in the fatty tissues of adult female bald eagles and resulted in thin shells and reproductive failure (Wiemeyer et al. 1972, 1984; Grier 1982). Due to the bioaccumulative and persistent nature of DDT and the adverse reproductive effects elicited by DDT, particularly on birds, its use was banned in the United States in 1972. Restrictions on organochlorine pesticides combined with concerted efforts to protect and manage habitat and to stop persecution have resulted in recovery of bald eagle populations throughout most of the contiguous United States. Hood Canal is a deepwater fjord characterized by restricted circulation and extreme water depths in western Washington. Although the number of occupied bald eagles nests in Hood Canal have been increasing, there was concern because their productivity remained significantly below the Washington State's productivity average in most years and fluctuated more dramatically than the Statewide values. In 1992, a contaminants study was initiated to evaluate if contaminants were a possible cause of the lower productivity.
The primary study objectives were to: 1) evaluate productivity of the Hood Canal territories, 2) determine if elevated concentrations of dioxins, furans, polychlorinated biphenlys (PCBs), organochlorine pesticides, and metals were present in bald eagle eggs collected from nests near Hood Canal, and 3) evaluate whether the contaminant levels present could be significantly contributing to the reproductive failures seen in the bald eagles from Hood Canal. An additional objective was to evaluate if resident bottom fish could be a source of contaminants.
Results: Concentrations of PCBs and compounds with dioxin-like activity were elevated at levels of concern in the eggs from the Hood Canal nests. Overall, the PCB concentrations in the eggs collected early in the study were at higher levels than those collected later. New nests continue to be established in the Hood Canal area. As older birds with substantial contaminant burdens are replaced by younger birds, we would expect to see a decrease in the persistent environmental contaminants in eggs if a constant or new source of the environmental contaminants available to the eagles is not present. Evaluations of other environmental contaminants that were not analyzed for in this study, but which could be potentially adversely affecting the Hood Canal bald eagles, should also be considered if a contaminants study is reinitiated. Evaluations of other factors, such as disturbance and habitat alterations affecting either nesting territories or prey, possibly should also be included if productivity is impacted.
Learn More by Reading the Full Report:Mahaffy, M.S., Ament, K.M., McMillan, AK, and Tillit, DE, Environmental Contaminants in Bald Eagles Nesting in Hood Canal, Environmental Contaminants. USFWS, Olympia FWO. 2000.
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