Signature whistle use by temporarily restrained and free-swimming bottlenose dolphins, Tursiops truncatus

Abstract

Prior work on the signature whistles of bottlenose dolphins has focused on captive or temporarily restrained wild dolphins. Here we examine whistle production by free-ranging adult bottlenose dolphins. Whistles were recorded from each of 13 dolphins while they were restrained and free-swimming. Eleven of the 13 animals produced whistles while free-swimming that matched whistles produced while restrained. On average, 51% of the whistles an animal produced while free-swimming matched whistles recorded while that animal was gently restrained. Of those free-swimming whistles that matched restrained whistles, 76% matched signature whistles. A further analysis was conducted to determine the social contexts in which free-swimming dolphins produced signature whistles. An adult, allied male was most likely to produce signature whistles when voluntarily separated from his partner, and least likely to when together with his partner. These results suggest that wild bottlenose dolphins use signature whistles as contact calls, similar to captive dolphins. The majority of whistles produced by a pair of allied males in a consortship with a female were variant whistles. A final analysis showed that signature whistles appear individually distinctive, consistent with their use as contact calls, while variant whistles do not.