Bats live noisy lives, often surrounded by sound, but they're not complaining: They're unaffected by the din, according to a new study out of Brown University on bat hearing.
The furry fliers use echolocation to make a nocturnal living, emitting high-frequency sounds and using the returned echoes off of objects to both navigate and hunt at night, mapping the world in front of them – whether tasty insects or physical obstacles - with "pictures" created out of sound.
That can get pretty loud, if you're a bat.
"They are naturally exposed to continuous, intense sound levels from their own and neighboring sonar emissions while foraging, orienting, and emerging from their roosts," wrote the authors of the study, just published in the Journal of Experimental Biology.
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On their own bats can emit up to 100 decibels, say the scientists, and in foraging groups that noise level can reach 140 decibels – the equivalent for humans of jackhammers or jet engines, respectively, for several hours at a stretch.
As anyone who's ever attended a rock concert sans earplugs knows, prolonged exposure to loud sounds can leave hearing diminished once the music stops.
The Brown University scientists wanted to know if bats had the same sort of thing happen to them - after, say, a night of foraging among their fellow bats.
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First they caught wild big brown bats (Eptesicus fuscus) and placed them in a lab, where the animals learned, via food rewards, how to move toward a natural spectrum of bat sounds played through a speaker.
Then, the researchers established a baseline sound level – the quietest sound the bats could still hear that would send them toward the speaker for a treat.
Baseline levels in hand, the scientists exposed the bats to a long period to the kinds of bat sounds they would hear out in the bat world.
Finally, they re-tested the bats' hearing after the noise exposure to see how much sensitivity the creatures had lost.
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It turned out that the bats' sensitivity remained largely the same – barely any hearing loss. Imagine a human going to a Metallica concert, without ear protection, and then leaving the show without a hint of "Huh?? What??" hearing loss and you get the idea.
For now, the scientists can only document the bats' ability to dodge deafness. They still don't know how the animals work their magic.
"We hypothesize that the bat's inner ear may have some special adaptations that allow it to protect itself from loud noises," said study co-author Andrea Simmons in a statement.
The researchers have more than just bat physiology on their minds. They hope a better understanding of the creature's hearing could help in the design of future devices and implants for human ears.