Sex and tool use status affect bottlenose dolphin (Tursiops aduncus) activity budgets and social network structure

Formation of associations within complex social groups varies between species, but sex is generally the greatest predictor of how individuals interact. Additionally, sex often determines the role of an organism it its group, and thus the time spent on different activities. Though, other features like tool use, in especially ‘intelligent’ species may also contribute to the social ties formed within a network and alter activity budgets. Within a large bottlenose dolphin (Tursiops aduncus) population in Shark Bay, Western Australia some individuals attach marine sponges to their rostra for protection, while scouring the seafloor for prey. The effect of tool use and sex, on social network structure and activity budgets within this population was explored, via photo-id surveys. Sex and tool use status were combined into a single variable, to determine whether the two features interact. Tests of difference were performed on activity budget and node level metric data. Tool use and sex both affected the associations of individuals, and their activity budgets. Sex and tool use interacted minimally within the activity budget data, and to a greater degree within the node level metrics. Thus, individual behavioural differences, in addition to sex, affect the behaviour and association decisions of bottlenose dolphin individuals. Further exploration of clique formation, in relation to other individual differences, is advised.