Are current contaminant concentrations in eggs and breeding female Lesser Scaup of concern?

摘要

One of the proposed explanations for the recent continental decline in Lesser Scaup (Aythya affinis) populations is that females experience lower survival or reproduction resulting from exposure to contaminants in their diet of exotic bivalves during migration and over winter. In 1999, we collected eggs and females from five sites in the boreal forest of Canada and Alaska and four sites in Canadian parkland. We analyzed eggs from 60 clutches and ten nesting females for toxic metals, selenium, 19 pesticides and other organochlorines, and 43 polychlorinated biphenyl (PCB) congeners. The highest organochlorine concentration we measured was 1.5 mug g(-1) ww of DDE in eggs. The highest mercury concentration was 1.8 mug g(-1) dw in liver. The highest cadmium concentration was 6.2 mug g(-1) dw in kidney. The highest selenium concentrations measured were 1.6 mug g(-1) ww in eggs, and 5.3 mug g(-1) dw in liver. All are well below thresholds known to cause embryotoxic and other effects in other bird species. Though sample sizes were small and did not include the entire breeding range or nonbreeders, our results provide no evidence to support the hypothesis of contaminant-induced effects on egg hatchability and female health. However, recently published concentrations of selenium in zebra mussels (Dreissena polymorpha) and Asian clams (Potamocorbula amurensis), predominant foods on staging areas, are sufficient to induce other sublethal effects, and possibly mortality if eaten by scaup for extended periods.