Echolocation behavior of pairs of flying Eptesicus fuscus recorded with a Telemike microphone.

Abstract

Four big brown bats (Eptesicus fuscus) were flown singly and in pairs in a room containing a sparse array of vertically hanging plastic chains as obstacles. Each bat carried a lightweight radio telemetry microphone (Telemike) that recorded their emitted echolocation sounds without artifacts from Doppler shifts, directional effects, and atmospheric attenuation. The broadcasts of both bats were also recorded with two stationary ultrasonic microphones located at the far end of the flight room. The echolocation broadcasts of bats flying singly were compared to those emitted when the bats were flown together. The principal change was shifting of harmonic frequencies very slightly (<5 kHz) away from each other and from frequencies used when flying alone. In contrast, the duration of emissions was more stable between single and double bat flights. Changes in ending frequency have been associated with a jamming avoidance response in big brown bats and could indicate attempts to avoid interference while flying with conspecifics in an enclosed space. [Work supported by ONR and NSF.]