Detection of atmospheric infrasound by homing pigeons

Homing pigeons (Columba livia) are sensitive to infrasounds at reasonable amplitudes. The testing procedure, using a conditional cardiac response (increased rate of beating), was similar to one used to test for sensitivity to barometric pressure changes. The pigeon was fitted with two ECG surface electrodes and two shock electrodes, restrained by a leather harness, and placed in a sound-insulated conditioning chamber 30 x 44.5 x 30 cm. Two methods of producing acoustic pressure oscillations were used--a motor driven piston and a loudspeaker driver. Homing pigeons can detect sound energy below 10 Hz at amplitudes well within the range of naturally occurring sounds at these frequencies. In fact, they can detect frequencies below 1 Hz. Unlike sounds easily audible to humans, atmospheric infrasounds can travel huge distances--often thousands of miles--without much attenuation; hence, such sounds could potentially provide birds with much useful information (storms, landmarks).