Jamming avoidance by the echolocating bat during flight with multiple conspecifics

It remains mystery how echolocating bats extract their own echoes from an acoustic jamming caused by vocalizations of multiple conspecifics flying together. Here, we first successfully recorded echolocation pulses of each animal during four-bat group flight by individually mounted on-board microphones, allowing us to assess vocalization in a jamming environment. We used Miniopterus fuliginosus which emit downward frequency-modulated (FM) ultrasounds. The bats experienced both single and group flights in an experimental chamber. As a result, each bat of the group significantly expanded differences in terminal frequency (TF) of pulses from the neighboring bat from 0.6 ± 0.6 (mean ± SD) kHz in single flight to 1.2 ± 0.6 kHz in group flight (Tukey’s HSD test, P < 0.05). Although the difference in TF observed in group flight was much smaller than the bandwidth of pulses (approximately 40 kHz), computation of cross-correlation providing an index of similarity of two signals demonstrated that the difference is useful to distinguish own signal from others. These results suggest that innate FM signal of bats is jamming-tolerant, and FM bats flying in group highlight differences in TF to avoid or reduce jamming from conspecifics in a closed space, as implied by previous studies.