Body Size, Activity Budgets, and Diets of Sea Ducks Wintering in Newfoundland

Morphology, diets, and activity budgets of four co—existing sea ducks, Harlequin Ducks, (Histrionicus histrionicus), Oldsquaws (Clangula hyemalis), Black Scoters (Melanitta nigra), and Common Eiders (Somateria mollissima), were studied during the fall and winter of 1983—1984 at Cape St. Mary's, Newfoundland. The diets and behavior of these species were related to body size. The smaller species, H. histrionicus and C. hyemalis, had diets with higher energy densities and spent more time feeding than did the larger M. nigra and S. mollissima. Multiple regression models were used to determine how the proportion of time spent feeding varied with five environmental and two temporal variables; we found that the two smaller species showed little flexibility in adjusting their activity budgets. This could become critical to survival of these diurnal feeders during periods of severe winter weather or ice conditions. As suggested by Bergmann in 1847, closely related species, such as these syntopic sea ducks in a harsh marine environment, adjust their behavior and diets to compensate for the thermodynamic differences associated with body size.