Implications of mercury and lead concentrations on breeding physiology and phenology in an Arctic bird / J.F. Provencher, M.R. Forbes, H.L. Hennin, O.P. Love, B.M. Braune, M.L. Mallory, and H.G. Gilchrist.

Includes bibliographical references (pages 1021-1022).

Although physiological traits and phenology are thought to be evolved traits, they often show marked
variation within populations, which may be related to extrinsic factors. For example, trace elements such
as mercury (Hg) and lead (Pb) alter biochemical processes within wildlife that may affect migration and
breeding. While there is a growing understanding of how contaminants may influence wildlife physiology,
studies addressing these interactions in free-living species are still limited.We examined how four
non-essential trace elements (cadmium, Hg, Pb and selenium) interacted with physiological and
breeding measures known to influence breeding in a free-living population of common eider ducks
(Somateria mollissima). We collected blood from female eiders as they arrived at a breeding colony in
northern Canada. Blood was subsequently assessed for baseline corticosterone (CORT), immunoglobulin
Y (IgY), and the four trace elements. We used model selection to identify which elements varied most
with CORT, IgY, arrival condition, and arrival timing. We then used path analysis to assess how the top
two elements from the model selection process (Hg and Pb) varied with metrics known to influence
reproduction. We found that arrival date, blood Hg, CORT, and IgY showed significant inter-annual
variation. While blood Pb concentrations were low, blood Pb levels significantly increased with later
arrival date of the birds, and varied negatively with eider body condition, suggesting that even at low
blood concentrations, Pb may be related to lower investment in reproduction in eiders. In contrast, blood
Hg concentrations were positively correlated with eider body condition, indicating that fatter birds also
had higher Hg burdens. Overall, our results suggest that although blood Hg and Pb concentrations were
below no-effect levels, these low level concentrations of known toxic metals show significant relationships
with breeding onset and condition in female eider ducks, factors that could influence reproductive
success in this species.