Year-to-year correlations in blood metal levels among individuals of two species of North American sea ducks.

Sea duck populations have declined in North America. Contaminants, especially metals, have been listed as possible contributing factors. Sea ducks are long-lived. Thus, individuals chronically exposed to elevated metal levels may be at greatest risk. Information about long-term exposure (> or =1year) of individuals to metals is absent. To address this information gap, we examined year-to-year correlations among individual White-Winged Scoters and King Eiders in levels of blood cadmium, lead, mercury and selenium. Positive correlations (r> or =0.43), were found in six, five, five and two of seven correlations for cadmium, selenium, lead and mercury. Thus, certain individuals of these species may be exposed over two or more years to higher levels of cadmium, selenium and lead (but apparently not mercury) than other individuals. Single blood samples are appropriate metrics of exposure for studies that examine long-term effects of certain metals on these birds.

Explaining co-occurrence among helminth species of lesser snow geese (Chen caerulescens) during their winter and spring migration.

The digestive tracts of 771 lesser snow geese (Chen caerulescens) collected from January to May 1983 from 12 locations (27 samples) were examined for helminth parasites to determine whether parasite species present in wintering geese or in spring migrants occurred independently of each other. Nine helminth species were identified. Seven had mean prevalences >5% and were the focus of this study. Six of those species were waterfowl generalists, one was a goose specialist. Our primary objective was to assess the potential contribution of factors, other than species interactions, in determining patterns of co-occurrence between helminth species. There were few negative relationships between helminth species, regardless of whether presence-absence or abundance data were used. However, some species pairs showed recurrent and significant co-occurrences. There were similar and significant effects of timing of sampling, host gender, and host age, on prevalence and mean abundance of particular species. Co-occurrences were found for those species that showed seasonal declines in prevalence, for those expected to have high colonizing ability based on host age profiles (using abundance data), and for abundant species that may have shared vectors or environmental conditions favorable for transmission. Thus, similarities between parasites in their abundance, transmission biology, and phenology seem sufficient to explain species co-occurrences without invoking other processes such as species interactions.