Female mate preferences and subsequent resistance to copulation in the mallard

In the majority of socially monogamous bird species, females solicit or accept copulations from males other than their partner. Females may gain direct benefits from extrapair males, such as greater access to resources, or indirect genetic benefits that will influence the future success of their offspring. However, one group of birds appears to be the exception to this general rule; in the wildfowl (Anseriformes), all extrapair copulations appear to be resisted by females. It has been suggested that resistance behavior may be a strategy to allow females a greater choice of mates, either at the precopulatory level (to promote choice of copulation partner) and/or the postcopulatory level (to promote multiple mating to increase their choice of sperm). This paper examines the function of female resistance behavior in one of the dabbling ducks, the mallard (Anas platyrhynchos). Observations on a marked population of wild mallard and experiments with captive birds found that although females showed a strong preference for particular males that are the first to molt into their breeding plumage, male attractiveness did not influence female responses to pair or extrapair copulation attempts. Female resistance decreased the likelihood that copulation attempts would end in successful insemination. The findings did not support the hypothesis that females resist copulations to promote female choice and the reasons why waterfowl may benefit from avoiding all extrapair copulations are discussed.