Productivity, diet, and environmental contaminants in bald eagles nesting near the Wisconsin shoreline of Lake Superior
Bald eagles (Haliaeetus leucocephalus) nesting in the Apostle Islands National Lakeshore and along the Wisconsin shoreline of Lake Superior produced an average of 0.8 young/occupied nest and had an average nest success of 57% during 1983–1988, compared to 1.3 young/occupied nest and 77% nest success in inland Wisconsin. Contaminant levels in nestling bald eagle carcasses collected from nests near Lake Superior were higher than those collected inland, suggesting local contamination. Prey remains collected at nests consisted of fish (50%); birds, primarily herring gulls (Larus argentatus) (48.4%); and mammals (1.2%). Organochlorine and polychlorinated biphenyl (PCB) residues were present at low levels (DDE: ¯x=0.07 μg/g wet wt, PCB:¯x=0.21 μg/g wet wt) in fish. Herring gulls contained higher concentrations (DDE∶x=5.5 μg/g wet wt, PCB∶¯x=16.95 μg/g wet wt) and appear to be the major source of elevated contaminant levels in bald eagles nesting near Lake Superior.