Reproduction, organochlorines, and mercury in northwestern Ontario Bald Eagles

A yearly census of Bald Eagles (Haliaeetus leucocephalus) in northwestern Ontario revealed a significant decline (P < 0.05) from 1966 through 1973 in the percentage of potential breeding areas that actually produced nestlings (range of 74% to alow of 36%).The average number of young per nest with young (1.5 overall) did not vary significantly during this period.Residue levels of several toxic chemicals except mercury were high in addled eggs, averaging on a dry-weight basis 94 ppm p,p'-DDE, 5.2 ppm dieldrin, 434 ppm PCB, and 2.5 ppm mercury.The shells of these eggs were significantly thinner (P < 0.05) than those of eggs collected before 1947.Toxicant residue levels of eagle eggs in this region are substantially higher than in the tissues of a dead nestling eagle or in the eggs of Ospreys (Pandion haliaetus) in the same region.The high PCB values suggest that the eagles are acquiring the toxicant burden outside of the nesting region.