Multiple mating and cooperative breeding in polygynandrous alpine accentors. I. Competition among females

The reproductive strategy of female alpine accentors, Prunella collaris, was studied on the summit of Mt Norikura in Japan. Alpine accentors formed polygynandrous groups consisting of three to six males and three to five females; however, each female laid eggs in her own nest. Within each group, females were organized in stable, linear hierarchies based on age. All females were sexually active but high-ranking females copulated more frequently with several males from the group. In contrast, the degree of multiple mating and frequency of copulations of low-ranking females was lower because their sexual activity was interrupted by more dominant females. All copulations were preceded by female solicitation. When the young hatched, males helped to feed the chicks of several females with whom they had copulated. The main factor influencing reproductive success was the amount of parental care that was available for feeding the chicks. High-ranking females had paternal help from two or more males and secured a high provisioning rate for the brood, which increased fledging success and nestling weight. The reproductive success of low-ranking females was lower because the brood did not receive sufficient paternal investment and so often starved to death early in the nestling period. These results suggest that the greatest potential benefit females might obtain from multiple mating is the subsequent assistance of several males in caring for the offspring. I discuss the implications of these observations with the idea that competition among females for males brings about multiple mating as a female reproductive strategy. Copyright 1998 The Association for the Study of Animal Behaviour.