Marine mammals stand out among nonhuman mammals in their abilities to modify their vocalizations on the basis of auditory experience. While there is good evidence that terrestrial mammals learn to comprehend and use their calls correctly, there is much less evidence for modification of vocal production (Seyfarth & Cheney, Chapter 13). In contrast, vocal learning has evolved independently in at least two marine mammal taxa, the seals and cetaceans, and is widespread among the whales and dolphins. We concentrate our focus in this chapter on vocal learning and development in the bottlenose dolphin (Tursiops truncatus) because it is the marine mammal species in which vocal learning and imitation has been best studied.
Dolphins produce a variety of sounds. The two predominant sound types are clicks, which can be used for echolocation, and frequency-modulated whistles, which are used for social communication. In addition to whistles, dolphins produce short frequency upsweeps that have been called chirps (Caldwell & Caldwell 1970). The dolphin vocal repertoire also includes a variety of burst pulsed sounds and combinations of pulses and whistles.
Captive bottlenose dolphins of both sexes are highly skilled at imitating synthetic pulsed sounds and whistles (Caldwell & Caldwell 1972; Herman 1980). Once a dolphin learns to copy a sound, the novel sound can be incorporated into its vocal repertoire, and the dolphin can produce the sound even when it does not hear the model. Bottlenose dolphins may imitate sounds spontaneously within a few seconds after the first exposure (Herman 1980), or after only a few exposures (Reiss & McCowan 1993).