tlenosed dolphin and other cetaceans. Results of work on absolute thresholds, critical bandwidths, frequency discrimination, and sound localization all indicate that the dolphin auditory system is at least as good or better than the human system. This is in spite of the fact that sound travels five times as fast under water as it does in air (Popov et al. 1991). The bottlenosed dolphin in captivity produces two 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, as cited in Schusterman et al. 1986). The pulsed sounds are used for both communication and echolocation, and the whistles are found to be used primarily for communication (Herman & Tavolga, 1980, as cited in Schusterman et al. 1986). Descriptions in literature emphasizing either the whistles or the pulsed sounds have led to contradictory hypotheses concerning the communication system of the dolphin. It has been reported that individually specific whistles often make up over 90% of the whistle repertoire of captive bottlenosed dolphins (Popov et al. 1991). A number of observations of apparent vocal mimicry have been made, though with no systematic investigation of the degree of vocal flexibility. The observed variability in the whistles, combined with the difficulty of identifying individual vocalizing dolphins in a group, has led to speculation that the whistles might be a complex, shared system, in which specific meanings could be assigned to specific whistles. Consideration of vocal mimicry has been taken to understand its relation to cognitive complexity, and to the potential use of vocal response for communication in an artificial language. In one study done by McCowan, Hanser, & Doyle, (1999), the dolphin was able to learn to mimic a number of computer-generated model sounds with high fidelity and rel...
