Anyone who has ever been in the presence of a bunch of bats knows that they can be chatty little things; even though we can't even hear all the noises they emit, they make quite a concert. Scientists already know that Mexican free-tailed bats, for example, have at least 15 types of social calls. But now a new study finds that bats can also use their calls in a rather nefarious manner.
When bats are hunting insects in the dark, they emit a series of rapid ultrasonic calls that echo back the bug’s exact location. Known as the "feeding buzz,” the sounds are necessary for hunting, but they also send out a “Hey, food here!” alert to other hungry bats, thereby increasing competition for the food. You might think that the bat initially honing in on the prey would have the advantage, but alas, no. As it turns out, nearby bats can send out a jamming signal that causes the hunter to miss its meal, allowing the interfering bat to swoop in for the kill. Clever creatures.
The possibility of this jamming signal first came to light for Dr. Aaron Corcoran, a biologist at Wake Forest University in Winston-Salem, North Carolina, while he was recording bat-moth interactions in Arizona.
"One bat was trying to capture an insect using its echolocation. The second bat was making another sound that looked to me like it might be trying to jam or disrupt the echolocation of the other bat," said Corcoran. "Most of the time when another bat was making this jamming call, the bat trying to capture the moth would miss," he added.
Cocoran and other researchers recorded bats on video along with ultrasonic microphones, and then compared the bats’ calls to their flight paths. They made a 3-D reconstruction and concluded that indeed, hunters make the feeding buzz, and competitors emit a blocking signal. Corcoran and William Conner, a biologist at Wake Forest University, realized that the bats were more competitive than cooperative, readily using their disruptive jamming call, reports the journal, Science. “They use it at the moment of truth, when the hunter is zeroing in on its prey,” Conner says.
“It’s a thrilling finding,” says Mirjam Knörnschild, a bat vocalization expert at the University of Ulm in Germany. “Sonar interference has always been an exciting possible explanation … for the fact that certain bat species are highly vocal, and this elegantly designed study is a convincing demonstration.”
The blocking signal works by overlapping the initial hunter’s final feeding buzz, creating sound waves that jumble the auditory processing and reduces the ability to target the insect’s position with its echolocation. But even once the first hunter’s signals has been jammed, there’s nothing stopping that bat from turning around and blocking the interloper’s feeding buzz. Ultimately, they can go back and forth sabotaging each other’s hunt until one of them gives up.
"Nobody has seen anything like this in any other animals which echolocate. It's not necessarily surprising that they're competing with each other, but the fact that they've evolved this jamming signal is quite new,” Corcoran told the BBC.
While there’s still so much to understand about the social calls of bats, the jamming signal is “cool,” says Connor. “We think engineers are pretty clever when they use a signal to jam sonar and radar. But bats came up with this idea 65 million years earlier.”
Watch (and hear!) the bats in action in the video below:
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