Local Distribution, Food Choice and Food Consumption of Diving Ducks on a South Swedish Lake

The local distribution, food choice and food consumption of Aythya fuligula, A. ferina and Bucephala clangula in relation to available food resources were studied on a south Swedish lake that was used by these species and Mergus merganser during migration and by A. fuligula and B. clangula for moult. A. fuligula had a diet markedly dominated by chironomid larvae and Pisidium spp., the latter taken in larger proportion than their share of the bottom fauna. B. clangula mainly fed on larvae of chironomids and Trichoptera, whereas A. ferina took seeds and chironomid larvae. From early August to late November, the west Lake Ringsjodn was exploited by 125,800 bird-day units with an assumed consumption of 200 g/day per bird or 26 metric tons, compared to a total standing crop of food species in September of 82 tons. An increase in the standing crop was noted during the period., except in Pisidium spp., the preferred food of A. fuligula.