Corticosterone in relation to tissue cadmium, mercury and selenium concentrations and social status of male lesser scaup (Aythya affinis)

Combined lesser scaup (Aythya affinis) and greater scaup ( A. marila) populations have declined steadily from the 1970s. Accompanying the population decline have been two shifts in lesser scaup demographics: a decrease in the proportion of young birds and an increase in male to female ratio. In addition, there are concerns about potential effects of contaminants and trace elements. These metals may influence the stress response and corticosterone secretion. We examined impacts of cadmium, selenium and mercury on the stress response in relation to social status in male lesser scaup near Yellowknife, NWT May to June 2004 and 2005. Kidney cadmium and liver selenium and mercury ranged 0.78-93.6, 2.12-9.64, and 0.56-3.71 mu g/g, dry weight, respectively. Results suggest that corticosterone release may be influenced by complex contaminant interactions in relation to body condition and body size. When cadmium was high and birds were in good body condition, there was a negative relationship between liver selenium and corticosterone (R-2 = 0.60, n = 10, P = 0.008) but not in birds with poor body condition (R-2 = 0.07, n = 9, P = 0.50). Unfortunately we were unable to draw any conclusions about metals and social status in relation to corticosterone or glucose and T-4. This study emphasizes the complex nature of biological systems and the importance of considering interactions to characterize effects of metals.