Mexican free-tailed bat. Credit: Nickolay Hristov
Bats aren't just amazing—they're competitive. The winged mammals can jam the sonar of rival bats to keep them from catching prey, a in Science finds.
To pinpoint their targets, bats give off ultrasonic calls and listen to returning echoes. This talent for echolocation lets them hunt in complete darkness. Past research had shown that bats will change the frequencies of their ultrasonic calls to avoid interfering with their compatriots. But now, researchers say they have discovered that bats could be jamming competitors on purpose.
"This is the first time that anyone has seen sonar jamming in a competitive interaction," says study author William Conner, a biologist at Wake Forest University in Winston Salem, N.C.
Scientists investigated , which form the largest known bat colonies in the world—some caves house more than 1 million creatures. Social interactions among so many bats are complex, as you might imagine, involving at least 15 different kinds of calls. But there was one specific signal that scientists couldn't explain.
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To figure out the puzzle, they recorded video and audio of the bats as they competed for prey at two foraging sites. The scientists used an ultraviolet light to attract insects and feeding bats in a canyon in Arizona, and a street lamp to achieve similar results in a high school parking lot in New Mexico. That sounds like a lot of trouble, but it was easier than taking a bunch of equipment deep into a cave or high in a tree.
"Studying bats in the their natural environment is challenging — it requires high-speed infrared-sensitive video cameras and ultra-high-frequency microphones, and you have to get up pretty high to eavesdrop on Brazilian free-tails," Conner says. (Bat interactions were seen up to roughly 80 feet above the ground.)
The scientists discovered that the new signal is a jamming sound that bats give off when another bat emits a "feeding buzz," a fast call that gets faster as the bat goes in for the kill, helping it home in on insect prey during the final moments of a chase. The jamming signal sweeps across all the sound frequencies used in a feeding buzz, likely interfering with pinpointing a target's position. Competing bats often take turns jamming each other until one of them gives up.
Bats were up to 85.9 percent less likely to capture insects when rivals gave off jamming sounds. When the researchers played back recordings of jamming signals, prey capture success decreased by 73.5 percent.
"Bats have solved the puzzle of sonar jamming in one of the ways that sonar and radar engineers have used — bats just found the solution 65 million years earlier," Conner says.
And this isn't the only instance of sonar jamming in nature—previously, scientists found that moths can rub their genitals together to ward off bats. Bat biologist , a professor emeritus at Western University in Canada who did not take part in this study, says sonar jamming may be pervasive among species that echolocate.
"It may even go beyond bats," Conner says. "Toothed whales like dolphins also use echolocation."
Given that these bats might have to compete with as many as one million hungry roost-mates, it makes sense they might seek any edge they can get over their rivals. "Competition for food is found throughout the animal kingdom," Conner says. "It can mean the difference between life or death."