A mechanism for antiphonal echolocation by Free-tailed bats.

Bats are highly social and spend much of their lives echolocating in the presence of other bats. To reduce the effects of acoustic interferences from other bats' echolocation calls, we hypothesized that bats might shift the timing of their pulse emissions to minimize temporal overlap with another bat's echolocation pulses. To test this hypothesis we investigated whether free-tailed bats (Tadarida brasiliensis) echolocating in the lab would shift the timing of their own pulse emissions in response to regularly repeating artificial acoustic stimuli. A robust phase-locked temporal pattern in pulse emissions was displayed by every bat tested which included an initial suppressive phase lasting more than 60 ms after stimulus onset, during which the probability of emitting pulses was reduced by more than fifty percent, followed by a compensatory rebound phase, the timing and amplitude of which were dependent on the temporal pattern of the stimulus. The responses were non-adapting and were largely insensitive to broad changes in the acoustic properties of the stimulus. Randomly occurring noise-bursts also suppressed calling for up to 60 ms, but the time-course of the compensatory rebound phase was more rapid than when the bats were responding to regularly repeating patterns of noise bursts. These findings provide the first quantitative description of how external stimuli may cause echolocating bats to alter the timing of subsequent pulse emissions.