Dolphin Vocal Mimicry and Vocal Object Labeling
Douglas G. Richards
Kewalo Basin Marine Mammal Laboratory,
University of Hawaii
Dolphins and other members of the cetacean order are among the most vocal of the nonhuman mammals and exhibit remarkable development of the sound production and auditory mechanisms. This paper reports on the training of a bottlenosed dolphin (Tursiops truncatus) to mimic a wide variety of computer- generated sounds and to vocally label displayed real-world objects using some of these same sounds. The description of the training results is followed by a consideration of the implications of the mimicry and labeling ability for cognition in dolphins, particularly in regard to the relation of mimicry to cognitive complexity, and to the potential use of a vocal response mode for two-way communication in an artificial language. Finally, I discuss the implications of a laboratory demonstration of mimicry for studies of the natural communication behavior of dolphins.
The bottlenosed dolphin in captivity produces two broad categories of vocalizations: (a) narrow-band, frequency-varying, continuous tonal sounds referred to as "whistles" and (b) broad-band pulsed sounds expressed as trains of very short-duration clicks of varying rates ( Evans, 1967; Lilly, 1962). The pulsed sounds are used for both communication and echolocation, and the whistles appear to be used primarily for communication ( Herman & Tavolga, 1980). Descriptions of vocalizations emphasizing either the whistles or the pulsed sounds have led to contradictory hypotheses in the literature concerning the communication system of the dolphin. Some descriptions concentrating on the whistle vocalizations of dolphins in captivity have stressed the stereotyped, individually specific nature of these sounds. It has been reported that individually