Measurements of the Ultrasonic Cries of Bats

Abstract

The ultrasonic sounds emitted by bats were analyzed with a system sensitive to frequencies from 1-150 kc. Echoes of these sounds are utilized by bats in detecting obstacles. The cues consist of pulses about 2 msec. in duration. Most of the measurements were made with the little brown bat, Myotis l. lucifugus. With this sp. the sound pressure at 40-50 kc., at 5-10 cm. from the mouth, averaged 60 dynes/sq. cm. The highest recorded intensity was 173 dynes/sq. cm. The frequency of the ultrasonic stimulus falls during each pulse by about 1 octave; the avg. frequency at the peak amplitude was 47.8 kc, while the avg. at the beginning of the pulse was 77.9 kc, and at the end 39.1 kc. Low frequency waves (about 10 kc.) accompany the pulse, but their amplitude is a very small fraction of the peak sound pressure at ultrasonic frequencies. The envelope form is variable, the emission is directional with most of the energy concentrated in the forward direction, and the pulses are commonly repeated at rates of 20-30/sec.