What Can Birds Hear?

For bids, hearing is second in importance only to vision for monitoring the world around them. ./\vim hearing is most sensitive to sounds from about 1 to 4 kHz, although they can hear higher and lower frequencies. No species of bird has shown sensitivity to ultrasonic frequencies (\u3e20 kHz). Sensitivity to frequencies below 20 Hz (dasound) has not received much attention; however, pigeons and a few other species have shown behavioral and physiological responses to these low frequencies. In general, frequency discrimination in birds is only about one-half or one-third as good it is for humans within the 1 - 4 kHz range. A problem that birds suffer that is similar to humans is damage to the auditory receptors (hair cells) from loud noises. The sound intensity that produces damage and the amount of damage produced differs depending on the species. Buds residing in the active areas of airports might be constantly subjected to sound pressure levels that damage their hearing. Thus, to effectively disperse birds using sound, auditory alerts must be at frequencies that can he detected by the damaged auditory receptors. Although some if not all species of birds have the abhty to repair damaged hair cells, continued exposure to loud noises would prevent recovety of their hearing. In this paper I review what is h o w about avian hearing and compare that to the operational charactenstics (frequencies, intensities, duration) of techmques and devices to disperse buds