Replacement dolphins? Social restructuring of a resident pod of Atlantic bottlenose dolphins, Tursiops truncatus, after two major hurricanes



Environmental variations can influence the structure of ecological communities that in turn alter the grouping and association patterns of social communities. This study compares the social structure of bottlenose dolphins in the Bahamas before and after two major hurricanes. Approximately 30% of regularly seen individuals disappeared after the hurricanes, with an equal number of immigrants arriving afterwards. The primary goal of this study was to quantitatively describe social structure changes occurring after this large-scale emigration (or death) and subsequent immigration of individuals using the social analysis program, SOCPROG 2.3. The pre-hurricane results revealed one community with association patterns that were consistent with previous work on this population as well as other well-documented populations. Post-hurricane associations revealed that the community split into two distinct units, whose members associated highly within, but rarely between units. Association patterns varied between units. Immigrants assimilated well into the population, especially males. Over half of the post-hurricane associations involved immigrants, the majority between residents and immigrants, and primarily involving immigrant males. The costs/benefits of choosing to associate with an immigrant individual differ between males and females and may have been the driving force for the changes in social structure that occurred.