Abstract:

The manner in which bats process their echolocation calls involves two main components: (1) producing and transmitting the signals; and (2) receiving and analyzing them [Fenton and Brock, Bats, Facts On File (1992)]. The high-frequency signals constituting these calls consist of constant frequency (CF) sounds and frequency modulated (FM) sounds. CF components were found to be used for prey detection and identification; FM components were found to be utilized to update distance information. The Doppler shift also helps in detection of targets and gauging the speed of moving targets. Thus, combining the pulses and the resultant echoes enables the bat to determine object distances, sizes, and shapes. Bats were found to have their own call frequencies and are insensitive to a wide range of potential jamming sounds, which allows them to clearly distinguish their own calls amidst environmental cacophony. Experiments have shown that only when entire CF/FM simulations were used did the bats perform discrimination tests badly [J. D. Altringham, Bats: Biology and Behavior (Oxford U.P., New York, 1996)]. This indicates that the echolocation process may be essentially a series processing of CF/FM signals rather than parallel processing of both types.