Signature whistles facilitate reunions and/or advertise identity in Bottlenose Dolphins

Abstract

Animals with stable relationships need mechanisms to stay in touch when separated. Five decades of research suggest that signature whistles are likely candidates for serving this contact-calling purpose in bottlenose dolphins. However, difficulties identifying the vocalizing individual and measuring inter-animal distances have hindered tests of call functions among wild dolphins. Moreover, signature whistles almost certainly serve a variety of functions, so that to focus on contact calling, it is useful to identify contexts where animals need to maintain cohesion. By simultaneously tagging pairs of mothers and calves to look at instances when the animals are separating and reuniting, we focus on testing specific contact functions of signature whistles. Drawing from the literature, we define three potential contact call functions for signature whistles, each with its own hypothetical signature whistle distribution during separations and reunions: location monitoring, reunion calls, and identity advertisement calls. To test these potential functions, we estimated the probability of an animal producing a signature whistle at different stages of temporary separation events. Using a binomial logistic regression model, we found that the data are consistent with signature whistles functioning as reunion calls or identity advertisement calls but not for location monitoring during separations and reunions.