On-board telemetry of biosonar sounds from free-flying bats

Abstract

Analysis of the bat's reactions to relevant target echoes enables us to directly assess biosonar performance. Here, we recorded the sonar broadcast and its echoes the bat received during flight by using an on-board telemetry microphone (Telemike) mounted on the bat's back. Telemike recordings confirmed that flying bats adjust the amplitude and frequency of their sonar broadcasts to compensate for increases in echo amplitude and for Doppler-shifts. For insect capturing, the bat exhibited Doppler-shift compensation for echoes from the static target ahead, but not for echoes from the target moth even though the flying bat attended to the moth for capture. Positive and negative Doppler shifts (acoustic glints) caused by insect fluttering were observed in the constant-frequency component of observed echoes, which synchronized with wingbeat cycle of the moth. Combined frequency and amplitude compensation for the static target may be advantageous for detection of acoustic glints of target prey. We also constructed multiple-microphone arrays for tagging wild aerial-feeding insectivorous bats. Not only the location of the bat, but also direction and directivity of the bat's broadcast can be measured. This will allow us to investigate 3-D search algorithm of multiple targets by the bat. [supported by JSPS and ONR]