Rapid jamming avoidance in biosonar

TLDR

Bats and dolphins possess sonar systems that outperform man‑made sonar and radar, with sensitivity to noise and jamming being a key factor; prior work suggested bats adjust call structure to avoid jamming, but relied on behavioural correlations rather than controlled experiments. The study aims to provide the first experimental evidence of jamming‑avoidance responses in bats. The experiment presented Tadarida brasiliensis with playback stimuli of recorded echolocation calls at six different frequencies. Bats exhibited rapid jamming‑avoidance responses by shifting their call frequencies away from the playback, including upward shifts even when initially below the playback frequency, with spectral shifts occurring within less than 200 ms in the first call after a stimulus change.

Abstract

The sonar systems of bats and dolphins are in many ways superior to man-made sonar and radar systems, and considerable effort has been devoted to understanding the signal-processing strategies underlying these capabilities. A major feature determining the efficiency of sonar systems is the sensitivity to noise and jamming signals. Previous studies indicated that echolocating bats may adjust their signal structure to avoid jamming (‘jamming avoidance response’; JAR). However, these studies relied on behavioural correlations and not controlled experiments. Here, we provide the first experimental evidence for JAR in bats. We presented bats ( Tadarida brasiliensis ) with ‘playback stimuli’ consisting of recorded echolocation calls at one of six frequencies. The bats exhibited a JAR by shifting their call frequency away from the presented playback frequency. When the approaching bats were challenged by an abrupt change in the playback stimulus, they responded by shifting their call frequencies upwards, away from the playback. Interestingly, even bats initially calling below the playback's frequency shifted their frequencies upwards, ‘jumping’ over the playback frequency. These spectral shifts in the bats' calls occurred often within less than 200 ms, in the first echolocation call emitted after the stimulus switch—suggesting that rapid jamming avoidance is important for the bat.