Bats Hear Just Fine, Despite Noisy Lives

Prolonged exposure to intense sound levels doesn't harm their hearing, a new study finds.

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.

Did you know April 17 is bat appreciation day? And why not? These flying mammals, though they look a bit scary to some people, are actually most welcome critters, for all of the good they do. Bats are terrific pollinators and seed-dispersers of hundreds of plant species, and they eat tons of insects -- enough to match their own body weight on a good night of foraging. So on this day, appreciate them we will! Let's have a look at some more of these winged wonders.

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Bats love, love, love insects, but they'll also eat fruits, flower nectar, vertebrates, and -- yes, indeed -- blood.

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This female dwarf epauletted fruit bat is in a family way, at the moment. Pregnant bats usually carry just one child at a time. Once born, the moms will nurse the newbies until they're almost fully grown, as the little ones' wings need to be fully developed before they can hunt for food on their own.

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Bat colonies roost together, and can do so in unspeakably large numbers -- in the millions, in some cases and caves.

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And when they take wing at dusk, they do that together too, in huge swarms.

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There are more than 1,200 species of bat, the vast percentage of them insectivores.

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Bats have generally small teeth that will vary by species, but they're plenty well suited to tearing into bugs, fruit, or even skin if the bat is among the small group of species that dines on vertebrates such as frogs or birds.

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Bats' wings are a lot thinner than those of birds, which helps them move fast, with incredible precision. Of course their thinness makes them fragile and susceptible to tearing. But if the tears aren't too large, they heal quickly.

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Sadly, bats today are experiencing a health emergency that first came to light in 2006. In large numbers, they're being decimated by a condition called white-nose syndrome, a fungus that grows on the muzzles, ears, and wings and is fatal nearly 100 percent of the time. This northern long-eared bat in Illinois is affected by white-nose syndrome. While there has been some

encouraging research

into treatments, there is as yet no cure for the disease. Here's hoping one arrives soon, because we need bats!

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