Food-Seeking Activity of South Swedish Diving Ducks in the Non-Breeding Season

Abstract

Aythya maria, A. fuligula and A. ferina were mainly night-active in coastal areas of southern Sweden except during colder periods when they were partly day-active. On the lakes A. fuligula and A. ferina showed a higher daytime feeding intensity than at the coast. Bucephala clangula, Clangula hyemalis, Somateria mollissima, Mergus merganser, M. serrator, and M. albellus were day-active. The highest food-seeking intensities were found in the smallest species and in B. clangula the smaller females generally had a higher food seeking intensity than the larger males. B. clangula and A. fuligula showed a significant correlation between decreasing temperatures and increased food-seeking intensity. Especially the females of B. clangula reached very high food-seeking intensities during the coldest periods and they were then also found to leave the areas in larger numbers than the males. The flights between the resting places and the feeding grounds in both the day-active B. clangula and the night-active A. fuligula were correlated with sunset and sunrise and occurred at lower light intensities in late autumn and winter compared to early autumn and spring.