Oceanographer’s Choice

Not oceanic, but very cool acoustics-related story nonetheless: Researchers at Wake Forest University have determined that tiger moths actively jam bat sonar to avoid being eaten.

Bats, famously, use ultrasonic pulses to hunt insects using echolocation. Moths, also, have been recorded emitting ultrasonic noises when being hunted, but scientists previously did not know what purpose they served—startling the bats, signalling to the bats they taste bad (à la bright colors in other insects), or actually interfering with the bats’ echolocation. To find out, these researchers organized a bat v. moth cage fight: they tethered tiger moths (Bertholdia trigona) in a room and let big brown bats (Epitesicus fuscus) try to hunt them, recording the ensuing smackdown with infrared video and ultrasonic audio.

The bats, who had not hunted this kind of moth before, did not get better at it over time, as they would if the moth clicks were meant to startle them (they would have gotten used to the clicks eventually). Nor did their hunting success decline, as it presumably would if the moth noises were advertising bad taste (the bats would have learned that’s what the moths meant, and would have stopped hunting them). Instead, the bats had a consistently bad record of capturing the moths. Coupled with the audio and video recordings, it appeared that the moths were actively jamming the bat’s echolocation, timing their clicks extremely precisely to interfere with the bats’ hunting pulses.

I would be fascinated to know if marine prey species do anything similar to jam the sonar of predators like dolphins and whales.

Videos of a bat failing to capture a clicking moth, and succeeding in capturing a silenced one.

Wired news story here.