Signature Whistles

Abstract

The signature whistle is defined as the most common whistle type that an individual uses when in isolation. Signature whistles have now been documented in more than 300 individual bottlenose dolphins, Tursiops truncatus, in a variety of locations, both captive and wild, and there is evidence for them in four other delphinid species. Melba and David Caldwell in the 1960s first described signature whistles for several species of captive delphinids. They found that individual dolphins, while isolated for medical attention, produced primarily one stereotyped individually distinctive whistle contour. Signature whistles function both in individual recognition and in maintaining group cohesion. In playback experiments conducted during brief capture-release events in Sarasota Bay, FL, dolphins responded more strongly to whistles of related than non-related individuals. In addition to discovering signature whistles, Caldwell and Caldwell were the first researchers to investigate vocal development in bottlenose dolphins. They found that young dolphins produce tremulous, quavery whistles, and then gradually converge on a stereotyped whistle contour during their first year of life. However, little is known about what factors govern the “choice” of whistle contours by calves. Again, studies that utilize acoustic localization with concurrent behavioral observations promise to shed light on this interesting question. Signature whistles are an important class of vocalizations produced by bottlenose dolphins. Much work remains to be done in order to learn how these whistles develop and how they are used in the natural communication system of dolphins.