Assessing Foraging Tradition in Wild Bottlenose Dolphins (Tursiops truncatus)

We analysed the association patterns of 22 bottlenose dolphins (Tursiops truncatus) identified as resident in the waters of the Archipelago de La Maddalena (Italy) to verify the existence of defined groups with a particular foraging strategy: to feed from fishing trammel nets. Two relatively well-defined communities were identified. Bottlenose dolphins that were observed feeding from trammel nets constitute one of these communities, and the other is mainly made up by individuals who have never been seen foraging from nets. The influence of sex, habitat, school size, location, and the presence of calves over the bottlenose dolphins' feeding behavior was also analyzed. Only the presence of calves shows a significant effect. It alone explains 23% of the variability in the foraging behavior. This percentage is not high enough to conclude that the presence of calves in a community of bottlenose dolphins is what determines their foraging behavior, but it seems that their presence does incite the net-foraging behavior by the adults. This study provides evidence for socially learned tradition in foraging tactics within a community of wild bottlenose dolphins, and it demonstrates the advantage of using the Ward's minimum variance method of hierarchical clustering to assess the existence of association patterns among individuals.