Proceedings of the Vertebrate Pest Conference

For birds, hearing is second in importance only to vision for monitoring the world around them. Avian 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 (>20 kHz). Sensitivity to frequencies below 20 Hz (infrasound) 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. Birds 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 be detected by the damaged auditory receptors. Although some if not all species of birds have the ability to repair damaged hair cells, continued exposure to loud noises would prevent recovery of their hearing. In this paper I review what is known about avian hearing and compare that to the operational characteristics (frequencies, intensities, duration) of techniques and devices to disperse birds.