Effects of body condition and environmental variability on incubation behavior and nest success of arctic-breeding common eiders ( Somateria mollissima)

The effects of daily light, weather patterns, and body condition on the incubation behaviour of common eiders (Somateria mollissima sedentaria and S. m. borealis) were studied on Mitivik Island in East Bay, Southampton Island, Nunavut, Canada in 1998 and 1999. Females were trapped on the nest to determine the individual and population rate of mass loss. Females lost an average of 21 g day-1 (corrected for structural size), during incubation, for a cumulative loss of 28.7%. Nest attendance patterns of control and experimentally extended incubation females were monitored using behavioural watches (1998 and 1999) and devices placed in nests (Remote Incubation Monitoring System, 1999 only). Incubation constancy was high but decreased daily over the incubation period. Females took brief recesses every 1--4 days. Daylight was nearly continuous and no diurnal patterns of nest attendance were found. Therefore, weather was the primary environmental influence on the timing of incubation recesses. Extended incubation females demonstrated that eiders at this colony could increase their incubation effort when necessary. However, females used different incubation strategies: some utilized more reserves to maintain high incubation constancy, while others spent less time on the nest, thereby reducing the rate of mass loss. The latter were more likely to lose their clutches. These data provide baseline information for common eider nesting at East Bay, and the opportunity to compare reproductive characteristics with other eider populations to support current and future management and conservation efforts.