Detection of atmospheric infrasound by homing pigeons

ACOUSTIC waves of frequencies below 10 Hz are common in the atmosphere. They are generated by various sources, including wind, thunderstorms, weather fronts, magnetic storms, aurorae, ocean waves, earthquakes, and many of man's mechanical devices 1–3 . Many of these atmospheric oscillations are of high amplitudes (frequently well above 100 dB SPL at frequencies below 5 Hz, and above 120 dB below 1 Hz) but because they are outside the normal limits of human hearing they usually go unnoticed (although humans can detect extremely loud artificial infrasounds generated in test chambers, these sounds are louder than most natural infrasounds and verge on the threshold for pain) 4,5 . It has been suggested, however, that migrating and homing birds might make use of the cues provided by such infrasounds 6 . During our ongoing study of the sensory basis of avian orientation, we investigated this possibility. We report here that homing pigeons ( Columba livia ) are sensitive to infrasounds at reasonable amplitudes.