Mate choice and competition for mates in the boat-tailed grackle

Behavioural studies have implicated both female choice of mates and male competition for access to mates as proximate mechanisms of sexual selection. Few studies have examined the interactions between these mechanisms in a natural setting. In this study, I explored how dominance interactions between male boat-tailed grackles, Quiscalus majordetermine the mating success of males and how the behaviour of female boat-tailed grackles influences this process. Male grackles defended colonies of females and performed courtship displays to females that were building nests. These conspicuous displays incited dominance interactions between males, with the result that dominant males interrupted subordinate males' attempts to copulate. Female grackles were receptive only to males that performed courtship displays, but their receptivity to males did not vary with male dominance rank or tail length. Females were more likely to be receptive in a colony than away from a colony, and females became receptive asynchronously during the breeding season. The timing and spacing of females' receptivity to males permitted dominance interactions between males to determine male mating success. By establishing the conditions for male competition, females indirectly chose high-ranking males. Recent studies have emphasized discrimination among potential mates as a behavioural mechanism for mate choice. The results reported here, however, demonstrate that other aspects of females' behaviour can produce mate choice, indirectly rather than directly.1997The Association for the Study of Animal Behaviour