Homophily in lagoon use-Namibian bottlenose dolphins

This data supports the research conducted in the following paper - Submitted to Animal BehaviourHomophily drives use of a risky shallow-water environment by common bottlenose dolphins (<i>Tursiops truncatus</i>) in NamibiaSocial mammals often associate with similar individuals, a tendency known as homophily. Homophily drives social structure in populations and provides fitness benefits by improving inter-individual cooperation and decreasing the cognitive effort required to evaluate collaborators. We investigated the factors (age class, sex, habitat preference, local space use overlap and stranding history) influencing the use of a high-risk tidal environment by a resident population of common bottlenose dolphins (<i>Tursiops truncatus</i>) from Walvis Bay, Namibia. We combined photographic mark-recapture with social network analysis and applied multiple regression quadratic assignment procedures to investigate homophily in this population. Bottlenose dolphins of the same age class, sex and habitat preference were more strongly associated, and the core of this population's social network was comprised of lagoon users (individuals regularly using both the Walvis Bay lagoon and bay habitats). Although males and subadults (of both sexes) were the most frequent users of this habitat, females with dependent calves also regularly utilised this habitat. Additionally, the majority of previously stranded dolphins (71%) were still observed using the lagoon habitat, despite having experienced the risks of potentially life-threatening stranding events. We suggest that the use of this potentially risky, but resource rich habitat may be socially learned, however the mode of transmission of this behaviour (vertically or horizontally) has yet to be investigated. Specialised foraging strategies such as this are often the first step towards separation of a population into behaviourally segregated communities, which may lead to fine-scale genetic differentiation over time.