This Is What Bats Jamming Each Other’s Sonar Sounds Like

When two bats swoop in for a bit of food, they engage in a sonar dogfight.

Nov 6 2014, 9:41pm

Image: Nickolay Hristov

When a colony of one million Mexican free-tailed bats swoops in on unsuspecting insect prey, they don't do it quietly. The chorus of squeaks emitted by a group of bats is generally understood as being comprised of social calls and, perhaps more importantly, echolocating signals that allow them to navigate their environment. Researchers have just identified one more more call in bats' repertoire: a jamming signal that bats use to interfere with competitors' sonar and ensure that they snag their prey.

Here's what it sounds like, slowed down 20 times so humans can hear it:

It's kind of pretty.

The jamming signal was discovered by Aaron Corcoran and William Conner, biologists at Wake Forest University in Winston-Salem, North Carolina. During initial field observations, the pair noticed that a specific kind of call that they dubbed the "sinusoidal frequency-modulation" (sinFM) call, after the shape of its waveform. According to their paper, published today in Science, bats only made the sinFM call when another bat in close proximity was rapidly emitting echolocation calls right before they tried—and failed—to snag a bug.

The researchers tested their observations at two bat foraging sites in Arizona and New Mexico. At the first site, they collected data with a microphone array and low-light videography. During the second field test, they used those findings to generate sinFM calls as bats swooped in for a moth they set up as bait and recorded their reactions. The bats were 77.3 percent less likely to capture the moth in the presence of the jamming call.

Footage of a bat missing its prey when a sinFM signal is emitted. Audio and video is slowed down 20 times.

Corcoran and Conner discovered that bats engage in what amounts to a sonar dogfight while competing for food by reconstructing the bats' flight paths using audio they recorded at the first test site.

"SinFM calls do not cause bats to leave the foraging area or move away from prey, as has been shown for food defense social calls in other species," the authors wrote. "Instead, bats frequently circle back to the foraging area after missing prey while a competitor makes sinFM calls."

As competing bats swoop in, other bats emit sinFM calls, causing them to back off. The spurned bats then circle around and go in for another strike, hopefully jamming the other bats' sonar before they jam theirs. Although, the researchers note, the bats' behaviour indicates that they're more focused on capturing their meal than scaring other bats away.

The researchers' outdoor setup for capturing data on sonar jamming. Image: Aaron Corcoran

Corcoran and Connor suggest that the jamming signal works by stimulating the same auditory neurons that bats use to spatially locate their prey, effectively messing them up enough that they fly right by their target. The sinFM call's rapid frequency modulations are so quick that a full cycle occurs in the listening window between echolocation feeding calls. The lowest point of the modulation rate is close to that of a regular feeding call, leading to auditory confusion.

So, next time you see a swarm of bats—and, for your sake, I hope you don't because that shit would be terrifying—keep in mind that what you're likely seeing is a complex game of attack and counterattack, as bats swoop in for a bite of a tasty bug while trying to jam their competitors' sonar.