Behaviourally specific preferred associations in bottlenose dolphins, Tursiops spp.

We investigated association patterns of 52 photographically identified, free-ranging bottlenose dolphins (Tursiops spp. Gervais, 1855) across four behavioural states (rest, travel, social, and foraging/feeding) to investigate how behavioural state influences patterns of association. Group composition and behavioural data were extracted from 2178 encounter surveys collected over 3 years. Analyses revealed three general types of association: (1) affiliates, which consistently demonstrate preferred associations across all behavioural states; (2) acquaintances, which never form preferred associations but still associate in at least one behavioural state; and (3) behavioural associates, which form preferred associations in at least one, but not all behavioural states. The majority of associations in Shark Bay, Australia, are acquaintance type (38.2%), with affiliates (5.7%, principally between adult males) and behavioural associates (28.9%, principally between juveniles) being relatively rarer. Permutation tests identified behaviourally specific preferred associations during all behavioural states. Although behaviourally specific preferred associations appear to exist within the Shark Bay social structure, it seems that the social organization and mating system constrain the social relationships for the majority of males and females in differing ways which prevent them from having behavioural associates, leaving juveniles free to associate based on short-term expediency and behavioural specific needs.