Recognition of Species of Insectivorous Bats by Their Echolocation Calls

The use of frequency, duration, and patterns of frequency change over time to identify 39 species of North American and African bats by their search phase echolocation calls is described. The data were obtained from an oscilloscope display of the cells presented by a zero-crossing period meter when the calls had been detected by a broadband microphone. Species using high intensity calls are more easily sampled than those using calls of intermediate intensity; bats using low intensity calls are not readily sampled by this system. Identification of bats in the field by their calls requires observation of known individuals under field conditions. The echolocation calls included frequency components from 8 to 210 kHz. At all sites, species using frequency modulated (FM) calls with frequencies from 25 to 65 kHz predominated; larger faunas exhibited greater variability in types of calls. The identification of echolocating bats by their calls depends upon the size of the bat fauna, the levels of bat activity, and inherent characteristics of the calls.