Dispersal in bottlenose dolphins: Bisexual locational philopatry, male-biased mother-offspring disassociation, and the role of fission-fusion dynamics

Dispersal is an important life history process in which an individual moves from a site (locational dispersal) or group (social dispersal) to another site or group where it breeds. However, despite its importance, few have explicitly studied dispersal in cetaceans or in an open fission-fusion social system. In this study, we examined mother-offspring locational and social dispersal in Shark Bay bottlenose dolphins (Tursiops sp.). We found that both male and female dolphins maintained their natal home ranges as juveniles, and juvenile home ranges as young adults. Juvenile home ranges were also not different from that of their mother's. Despite substantial mother-juvenile overlap in ranging, offspring significantly decreased associations with their mothers after weaning, with sons associating less with their mothers compared to daughters. These data provide strong evidence for bisexual locational philopatry and mother-son disassociation in Shark Bay dolphins. While bisexual locational philopatry offers males and females the benefits of familiar social networks and foraging habitats, the costs of philopatry may be mitigated by mother-offspring disassociation, in which the risk of close inbreeding with sons and resource competition with daughters is reduced. As the first behavioral study of cetacean dispersal from birth to adulthood, our study highlights the advantages of having a society characterized by high fission-fusion dynamics, and emphasizes the need for clarity when describing dispersal in this and other species.