The role of signature whistle matching in bottlenose dolphins, Tursiops truncatus

Abstract

The addressing of individuals with learned signals is inherent to human social interactions. It allows individuals to solicit the attention of a particular social companion or to direct information towards an intended recipient. The ability to address individual conspecifics with learned signals is not limited to humans, however. In songbirds, the selective addressing of individuals is facilitated by song type matching but is very much a signal of aggressive intent. The matching of learned signals is also observed in bottlenose dolphins, which will match one another's highly individualized signature whistle. Copying in dolphins occurs between close associates, which suggests that it is an affiliative signal. It could, however, also serve to manage aggression. We investigated the valence of signature whistle matching by performing interactive playback experiments. We waited until an animal produced its signature whistle and then either played back a synthetic version of its own whistle (match) or a different signature whistle (control). A total of 110 playback experiments were conducted with seven different animals from two managed groups of dolphins. The responses to the playback treatments were significantly different. Animals produced a consistent vocal response to being vocally matched, by returning the match, with no associated signal of aggression and did not respond to control playbacks in the same way. There was also an optimum time interval (<1 s) in which a match was most successful in eliciting a vocal response. Our results show that signature whistle matching is an affiliative signal that allows bottlenose dolphins to address social companions. Furthermore, these matching exchanges are driven by temporal associations, which appear to be essential in allowing animals to direct signals to particular individuals in large communication networks.