Dwingt kleptoparasitisme Kuifeenden Aythya fuligula tot nachtelijk foerageren?

The question as to why Tufted Ducks Aythya fuligula prefer to feed by night during winter is discussed in the light of food stealing behaviour of Coot Fulica atra and gulls Larus spp.. Field observations of diving Tufted Duck, Goldeneye Bucephala clangula and Coot feeding on Zebra Mussels Dreissena polymorpha demonstrate that stealing of prey brought up to the surface may considerably reduce feeding efficiency (Tab. 1). The risk of loosing prey is high (Fig. 1), particularly when handling time before prey is swallowed is long. Tufted Ducks rely on tactile rather than visual cues when feeding on mussels (de Leeuw & van Eerden 1992) and may therefore prefer nocturnal feeding to avoid food stealing. It is argued that Goldeneye and Coot need visual cues for efficient feeding and are, therefore, day active despite the risk of food stealing. Swallowing prey under water (Goldeneye) and social feeding in dense flocks (Coot) are considered alternative tactics to avoid food stealing.