Bats and moths: extremely high pitch

02 July 2019

Interview with 

Heather Jameson, Naked Scientists

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Heather Jameson has been looking at the highest sounds and highest hearing on record...

The highest note ever sung by a female is often attributed to Mariah Carey's song Emotions, in which she hits a G7, that's a G note in the seventh octave. But the record for the highest note hit by a male tumps that by nearly a full octave. In December 2017, Wang Zhou Ling reached an E8, that's higher than most pianos go up to, but whether the sounds could actually be described as singing is another matter.

This pales in comparison to the highest notes in the animal kingdom though. That record is claimed by the clear winged woolly that which can reach a maximum frequency of 250 kHz, that’s almost 50 times the human record. And where Mariah Carey is famous for having an impressively large vocal range, the bats can sweep through a frequency range of up to 170 kHz, which is over 50 times Mariah's range. These bats also share the record of world's fastest chatterers with many other bat species. They make repeated calls at a rate of up to one every 5 milliseconds, that's 12,000 every minute. But the bats aren't just gossiping, they're searching for food using sound. They listen carefully to the echoes to work out how far away an object is, what direction it is in, and how big it is. Why does such a high pitch help with this?

Well, the clear winged woolly bats live in tropical forests so they need to track bugs and other prey in the dense undergrowth. The high frequencies make the bats sonar being very focused and short ranged, but scientists believe this may help the bats scan the foliage bit by bit and to concentrate on a small spot where prey is, while suppressing distracting background echoes from the vegetation. The bats calls are way above the hearing range of humans, but moths have evolved to be able to hear the calls of bats in order to avoid being lunch.

The two have been locked in an arms race throughout the ages as evolution in bats raises the pictures of their call higher to avoid being overheard. Evolution in moths pushes the upper limit of their range up to match. But one species of moth, the greater wax moth, has seemingly outrun the competition by a wide margin. Scientists were perplexed to discover that this moth could hear sounds up to 300 kHz, that's higher than any animals is known to make, bat or otherwise. Scientists don't know why the moth would have evolved to detect such high frequencies, and the mystery is driving them batty.

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