COMMUNICATION IN DOLPHINS
Jeanette A. Thomas
Life in the water governs many of the characteristics of cetacean communication and has resulted in the evolution of unique adaptations for signal production and reception in an aquatic environment. For example, sound travels about four-and-a-half times faster in water than in air and range is frequency dependent. Low-frequency sound of sufficient amplitude (e.g., that of large mysticetes), if not masked by ambient noise, may be detected hundreds of miles from the source. Odontocetes produce broadband and very high amplitude sounds associated with echolocation. Hearing abilities are similarly broadband, requiring that elaborate processing be used to interpret echolocation signals.
In contrast, odontocetes do not have a well-developed olfactory sense. Although Tursiops has perianal glands which could conceivably function in chemocommunication, they probably are not used to the same extent as in terrestrial mammals for communication. Chemical signals in a marine environment tend to diffuse rapidly and would not be appropriate for a site-specific signal.
Distinctive color patterns in toothed whales (e.g., Orca, Phocoenoides, and Lagenorhynchus) suggest that visual signals are used in communication. However, vision varies among cetaceans (it has been lost in some of the river dolphins), and its usefulness may be restricted to short distances. Visual abilities have probably evolved as a compromised system that can be used in both air and water.