MARY LOUISE KELLY, HOST:
It's the stuff of nightmares.
(SOUNDBITE OF BATS SQUEAKING)
KELLY: Bats flying out of their caves by the thousands, sometimes tens of thousands. Across the world, it happens every night. And for the bats, you might think it was a nightmare, too - a traffic nightmare.
AYA GOLDSHTEIN: So they can be really close to each other. Usually, they are centimeter from one another when they just emerge.
AILSA CHANG, HOST:
Aya Goldshtein is a researcher at the Max Planck Institute of Animal Behavior, and she says the bats, they fly out fast. And they are packed together.
GOLDSHTEIN: Twenty-five bats a second emerge from the cave.
CHANG: But unlike our human highways, collisions are rare.
KELLY: Well, Goldshtein and her team wanted to know why. Their findings were published in Proceedings of the National Academy of Science. For starters, bats do use their eyes - they can see - but they also sense their environment with high-frequency sounds that echo off objects. That is echolocation.
GOLDSHTEIN: So when a bat emit an echolocation call, it wait to the reflected echo in order to get information about the object that is in front of it. And it can get information about the distance of the object, the size and the texture of the object, and it can say if this is an insect or a bat or a mountain in front of it.
CHANG: Normally, that is a navigation superpower, but imagine you're a little bat shooting out your ping, surrounded by thousands of your friends all doing the same thing. With so much sound bouncing back, how do you know which signal is yours?
GOLDSHTEIN: The bat will hear the echolocation of the other bat. It will not hear its own echo. And if you cannot hear your reflected echo of your echolocation, you don't have information.
CHANG: Just like other forms of signal interference, researchers call this jamming.
GOLDSHTEIN: We understood they probably cannot maneuver without colliding with this kind of severe acoustic interference, but we know that they do that. We know that they are rarely collide.
CHANG: So what's their secret?
KELLY: To find out, Goldshtein and her team staked out a cave in Israel, home to lots of greater mouse-tailed bats. The team attached tiny location trackers and microphones to their backs.
(SOUNDBITE OF ULTRASONIC SQUEAKING)
GOLDSHTEIN: These ultrasonic microphones that allow us to record the echolocation of the specific bat but also the other bats that fly around it.
KELLY: When the bats emerged, the team was able to record how they were moving and, crucially, how they were echolocating. And here is what Goldshtein found.
GOLDSHTEIN: At the moment that they leave the cave, there is, like, 94% jamming.
CHANG: But within seconds, they are able to reduce the jamming to 40%, and that's because they change how they echolocate.
GOLDSHTEIN: They increase a bit the frequency of the echolocation. The calls are shorter, and they're also weaker.
CHANG: That lets them focus right in on the bat in front of them.
GOLDSHTEIN: That's the most important information that they need.
KELLY: As long as they don't hit that bat, they tend not to hit anyone. Traffic jam averted. There is one other secret to their crash-free flying, Goldshtein says. Once they leave the cave...
(SOUNDBITE OF BATS SQUEAKING)
KELLY: ...They just spread out a bit.
(SOUNDBITE OF MUSIC) Transcript provided by NPR, Copyright NPR.
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