TESTING THE BEHAVIORAL DOMINANCE AND DISPERSAL HYPOTHESIS IN POCHARD

Wintering flocks of diving ducks often show a great disparity in sex ratio with males predominating. The behavioural dominance and dispersal hypothesis explains this phenomenon by arguing that males dominate and exclude females from limited food sources, forcing them to migrate further south. Our study of a wild flock of Pochard Aythya ferina under manipulated feeding conditions, provides some support for this hypothesis. Male attacks were directed more at females (74%) than at other males (26%) even though the sex-ratio favoured males 4.7 to 1. Male dominance appeared to influence the timing of female foraging activity rather than foraging location. Females appeared to feed after the requirements of males were fulfilled. We suggest, that in the long run, feeding second may be energetically expensive to females and cause them to migrate further, where food supply may be more abundant and male competition less.