Contaminant concentrations and reproductive rate of Lake Superior bald eagles, 1989-2001

We investigated the trend in contaminant concentrations in Lake Superior bald eagles (Haliaeetus leucocephalus) from 1989-2001, and examined the relationship of contaminant concentrations to eagle reproductive rate during that time. Concentrations of dichloro-diphenyl-dichloroethylene (DDE) and total polychlorinated biphenyls (PCBs) in nestling blood plasma samples decreased significantly from 1989-2001 (p = 0.007 for DDE, p = 0.004 for total PCBs). Mean contaminant concentrations in eaglet plasma, 21.7 mu g/kg DDE (n=51) and 86.7 mu g/kg total PCBs (n = 54), were near or below the estimated threshold levels for impairment of reproduction as determined in other studies. A preliminary assessment of polybrominated diphenyl ether (PBDE) concentrations indicated a mean of 7.9 mu g/kg total PBDEs in Lake Superior eaglet plasma (n = 5). The number of occupied bald eagle nests along the Wisconsin shore of Lake Superior increased from 15 to 24 per year, between 1989 and 2001 (p < 0.001, r(2) = 0.70, n 13 years). Eagle reproductive rate did not increase or decrease significantly between 1989 and 2001 (P = 0.530, r(2) = 0.037, n = 13 years, mean productivity = 0.96 young per occupied nest). The lack of correlation between reproductive rate and contaminant concentrations, as well as the comparison of contaminant concentrations to the estimated thresholds for impairment of reproduction, suggest that DDE and PCBs no longer limit the reproductive rate of the Lake Superior eagle population in Wisconsin.