Behavior and psychophysics of hearing in birds

Abstract

Psychophysical investigations of hearing in a number of avian species over the last decade have added significantly to our knowledge of hearing capabilities characteristic of this vertebrate group. Behavioral measures of absolute auditory sensitivity in a wide variety of bird species show a region of maximum sensitivity between 1 and 5 kHz with a rapid decrease in sensitivity at higher frequencies. On the basis of this general measure, birds fall between two other major vertebrate groups: reptiles and mammals. Discrimination and masking data from birds include measures of frequency, intensity, and duration difference limens; critical ratios, critical bands, and psychophysical tuning curves. There are also data on temporal summation, temporal resolving power, and temporary threshold shift from noise exposure. Taken together these data suggest that, in the region of 1–5 kHz, birds show a level of hearing sensitivity similar in most respects to that found for the most sensitive members of the class Mammalia with avian performance clearly inferior above and below this range of frequencies. Possible exceptions to this general picture must include the echolocating oilbird and growing evidence that pigeons are sensitive to infrasound at moderate intensity levels. The relation among critical ratio, critical band, and intensity difference limen measures in the parakeet is similar to that described for the human, but the pattern of masking as a function of frequency is dramatically different from that observed in mammals. Examples of a correspondence between hearing sensitivity and vocalizations can be demonstrated in a number of species.