ALREADY MATED FEMALES CONSTRAIN MALE MATING SUCCESS IN THE EUROPEAN STARLING

Most models explaining polygyny in birds have concentrated on variatio n in male or territorial quality, ignoring the role of females in main taining monogamy. Although field observations have suggested that alre ady mated females may maintain monogamy by either behaving aggressivel y toward prospecting females or by interupting male mate attraction be haviour, no experiments have been done to test if already mated female s constrain the mating success of their mates. In this study of the Eu ropean starling (Sturnus vulgaris), the possibility for already settle d females to defend their mating status was manipulated by changing th e distance between their mates' potential breeding sites. Solitary bre eding males were given an extra nest site at different distances from their present one: less than 2 m, 2-5.5 m and 7.5-15 m. The distance b etween nest sites was the most important determinant of male mating su ccess; few males became polygynous when nest sites were close together whereas most became polygynous when nest sites were further apart. In addition, secondary females were able to lay earlier in relation to t he primary females when their nest sites were further away from the pr imary females' nests. These results support the hypothesis that alread y mated females constrain the mating success of their mates.