How do bats avoid collisions while exiting a cave in thousands?

Bats do not fatally crash into each other every night, even in colonies of hundreds of thousands of them, squeezing out of caves to forage. Bats perceive their world mostly through echolocation. Many bats echolocate at once when a whole colony emerges from a cave. As a result, the calls of others are drowned out. Scientists call this loss of acoustic information “jamming”. When exiting the cave, bats experience a cacophony of calls, with 94% of echolocation being jammed. Yet, aerial accidents outside caves are so rare. Within five seconds of leaving the cave, bats significantly reduced the echolocation jamming. Researchers found that bats made two important behavioral changes — first, they fanned out from the dense colony core while maintaining the group structure; and second, they emitted shorter and weaker calls at higher frequency. Bats changed their echolocation to a higher frequency despite more calls only increasing the problem of jamming. The reason: a bat needs to know only about the bat directly in front. So the bats echolocate in such a way that gives them the most detailed information about only the bat in front. Though most of the information available is missed because of jamming, it does not matter because bats only need enough detail to avoid crashing into the bat in front. In other words, bats change the way they echolocate to gain detailed information about their near neighbours — a strategy that ultimately helps them to successfully manoeuver and avoid collisions.