CONTEXT-SPECIFIC USE SUGGESTS THAT BOTTLE-NOSED-DOLPHIN SIGNATURE WHISTLES ARE COHESION CALLS

Studies on captive bottlenose dolphins, Tursiops trumcatus, have shown that each individual produces a stereotyped, individually specific si gnature whistle; however, no study has demonstrated clear context-depe ndent usage of these whistles. Thus, the hypothesis that signature whi stles are used to maintain group cohesion remains untested. To investi gate whether signature whistles are used only in contexts that would r equire a mechanism to maintain group cohesion, we examined whistle typ e usage in a group of four captive bottlenose dolphins in two contexts . Individuals were recorded while they were separate from the group an d while they all swam in the same pool. Separations occurred spontaneo usly when one animal swam into another pool. No partitions were used a nd no aggressive interactions between dolphins preceded separations. C alling animals were identified by an amplitude comparison of the same sound recorded in the two pools. Each dolphin primarily produced one s tereotyped signature whistle when it was separated from the group. Sim ilarly the remaining group in the other pool also used primarily their signature whistles if one animal was in a separate pool. If all anima ls swam in the same pool almost only nonsignature whistles were used. Signature whistle copying was rare and did not initiate reunions pr sp ecific vocal responses. The results strongly support the hypothesis th at signature whistles are used to maintain group cohesion. (C) 1998 Th e Association for the Study of Animal Behaviour