Monitoring organochlorines in blood of sharp‐shinned hawks (Accipiter striatus) migrating through the great lakes

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Abstract
Blood samples from sharp‐shinned hawks (Accipiter striatus) were collected from 1985 to 1989 during the fall migration at Hawk Cliff, Ontario, and during the spring migration at Whitefish Point, Michigan, and analyzed for organochlorine contaminants. The study was designed to investigate the potential of using blood samples from birds of prey trapped by banders as a means of estimating the organochlorine exposure of migrant birds on their breeding and wintering grounds. Mean plasma levels averaged over the entire sample were highest forp,p′‐DDE (0.28 mg/kg, wet weight), followed by total polychlorinated biphenyls (PCBs) (0.08 mg/kg, wet weight). Mean levels of DDE, mirex, oxychlordane, heptachlor expoxide, dieldrin, hexachlorobenzene, and PCBs increased significantly in hatch‐year birds from their first southward migration to their return flight the following spring as second‐year birds. Thereafter, mean residue levels of the more persistent chemicals, including DDE, oxychlordane, and PCBs, did not change significantly between seasons in adult age classes. In contrast, dieldrin and heptachlor epoxide, which have a shorter half‐time in the body, increased significantly in the blood of all age classes after each winter and decreased significantly after each breeding season. The results were interpreted in terms of the clearance rates of the compounds as well as the diet of the birds on the breeding grounds. The sharp‐shinned hawk is a useful indicator species for contaminant‐monitoring programs involving birds of prey.