DISSERTATION RESEARCH: Playback Experiments to Examine Contextual Usage of Shared Whistles by Allied Male Bottlenose Dolphins, Tursiops Truncatus

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

PLAYBACK EXPERIMENTS TO DEMONSTRATE CONTEXTUAL USAGE OF SHARED WHISTLES BY ALLIED MALE BOTTLENOSE DOLPHINS, TURSIOPS TRUNCATUS. Peter L. Tyack and Stephanie L. Watwood Biology Department, Woods Hole Oceanographic Institution. Woods Hole MA 02543. Dolphins and whales (known to biologists as the cetaceans) constitute one of the few mammal groups that demonstrate highly developed vocal learning abilities. Dolphins not only learn to produce an individually distinctive signature whistle as infants, but adults retain the ability to imitate sounds. There has been growing interest in the role of vocal matching during the formation of social bonds in birds and humans, and dolphins provide an opportunity for studying this issue in a mammal that independently evolved abilities of vocal learning (Tyack 2000). Call imitation is used in bird species primarily between individuals with close social relationships or between territorial competitors. Most evidence suggests dolphins match calls either to initiate an interaction with another individual, or as a "badge" of group membership. When dolphins are interacting, they may imitate the individually distinctive whistle of an animal with whom they share a strong bond. Smolker and Pepper (1999) described whistle convergence in socially interacting male dolphins which formed a close-knit alliance, suggesting that whistle sharing is important for individuals with close relationships. This study proposes to examine the use of convergent or imitated whistles by allied male bottlenose dolphins in naturally occurring reproductive contexts or other social contexts. Playback experiments will test whether allied male bottlenose dolphins use shared whistles to attract potentially receptive females or to guard females from competitor non-alliance males. It has been difficult to study the individual vocal responses of free-ranging animals until recently. This study uses a small, towed linear array that can determine the direction from which sounds are produced in the water column, allowing for the identification of individual signalers (Tyack and Miller 1998). The research will be carried out in Sarasota Bay, Florida, where a community of individually identifiable dolphins has been studied for 30 years. Playback stimuli will be generated from high-quality recordings from a variety of age-sex classes recorded during temporary capture-release events during the last 15 years. Analyses of these recordings for alliance males demonstrated a high degree of similarity between the whistles of alliance partners. This proposal makes use of recent developments in acoustic localization to obtain identified whistles from free-ranging, socially interacting bottlenose dolphins. The combination of focal behavioral sampling, acoustic localization, and playback experiments presents a new way to understand the role of imitation in social communication. Playback experiments have been invaluable in deciphering the use of specific vocalizations in birds and primates. The proposed research presents an opportunity to examine acoustic social behavior in cetaceans on a much finer scale than previously attempted with free-ranging animals. The results from this study will be much more comparable to similar studies in terrestrial species.