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Bats out of hell: it's official, bats are louder than a Meatloaf concert

Sun, 4th May 2008

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Scientists studying the sounds produced by bats has shown that they are amongst the loudest creatures on earth, pumping out 140 dB.

A Big Brown BatThankfully, because it's in the ultrasound range, we can't hear it, but if we could it would certainly be an uncomfortable experience.  The threshold for human noise-induced pain is about 130dB and, according to the Guinness Book of Records, the loudest ever rock concert was a gig by The Who which notched up a deafening 126 dB.

But writing in this week's PLoS One, Annemarie Surlykke and Elisabeth Kalko have found that some bats literally roar, producing sounds of 140dB.  The researchers made the discovery when they recorded the nocturnal hunting habits of 11 species of insect-eating bats in Panama.

The bats use high-frequency sounds like the airborne equivalent of sonar, and find their way around and hunt for food by listening to echoes of the sounds they produce bouncing back from nearby objects.  Measurements by the scientists show that the bats were producing sounds ranging from 25kHz to 70kHz and 125-140dB.  The highest frequency that can be heard by a human is about 20kHz, which is why we're not aware of the racket.

The researchers also found that, on average, the higher the frequency used by the bats the louder the noise they produced.  This is to be expected because higher frequency sounds are more rapidly damped-down as they travel through the air, which is why fog horns and other warning signals tend to use low pitches, which travel long distances more easily.

Overall, say the scientists, all of the animals had roughly similar ranges for their echolocation - up to about 10 metres - and they all cut down the intensity of the sound as they get nearer to their targets, so they do have a conscience when it comes to disturbing the neighbours!

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