Bird calls: their potential for behavioral neurobiology.

Birdsongs are always part of larger set of sound signals. Every bird uses a repertoire of calls for communication. Calls are shorter and simpler than songs, with a much larger range of functions. Whereas songs are specialized for application in reproduction and territoriality, calls also serve such functions as signaling about food, maintaining social cohesion, contact calls, synchronizing and coordinating flight, and the resolution of aggressive and sexual conflicts. Alarm calls of various kinds are a major component, including distress, mobbing, and hawk alarm calls. Call repertoires vary greatly in size, up to 20 or so distinct call types. Rough estimates for songbirds range between 5 and 10, but some birds, especially galliforms, may have twice as many. Call usage is often sexually dimorphic and commonly varies seasonally and with physiological state. Most calls appear to be innate, but more and more examples of developmental plasticity in bird calls are emerging. Some display well-defined local dialects. A case is made for the value to avian behavioral neurobiology of including bird calls in studies of the psychophysics and sensory physiology of signal perception. They may also help to extend the range of neurobiological investigations of the song system to include circuitry controlling such functionally related behaviors as aggression and reproduction.