Bats use superfast vocal muscles to find their way and their prey in the dark, researchers at the University of Southern Denmark and the University of Pennsylvania have found.
"We discovered that Daubenton's bat (found throughout Eurasia) controls its echolocation calls with the fastest-contracting muscle type described," says Coen Elemans, lead author on the study.
Elemans and his colleagues are publishing their findings in the Sept 30 edition of the journal Science.
Superfast muscles have amazing adaptations making them capable of contractions about 100 times faster than our normal body muscles and up to 20 times faster than human's fastest muscles: those that move our eyes. These extreme performing muscles were previously known only from the sound-producing organs of rattlesnakes and several fish. "But recently we also found them in birds who use them to sing their beautiful songs. And now we have discovered them in mammals for the first time," Elemans adds, "suggesting that these muscles -- once thought extraordinary -- are more common than previously believed."
Just before capture, bats position flying insects using echolocation calls produced at rates up to 190 calls per second. This final phase of attack is called the terminal buzz. "It was unknown how bats are able to produce calls so quickly," explains John Ratcliffe, senior author on the study. "We figured that this rate would be limited by the bats ability either to process the returning echoes or produce the calls themselves," he adds.
The biologists measured when echoes are returning to the bats' ears in free flying bats. "Our data suggest that bats could theoretically produce calls much faster -- up to 400 calls a second -- before the returning echoes would become confusing to the bat," says Ratcliffe.
Next, they looked at how bats make their calls and measured the performance of their vocal muscles. "We determined the power the muscles can deliver, much like how you measure a car's performance," Elemans explains. "We were surprised to see that bats have the superfast muscle type and can power movements up to 190 Herz (times per second), but also that it is actually the muscles that limit the maximum call rate during the buzz," he adds.
"Before the bats evolved more than 50 million years ago, the night skies were full of flying moths and other insects," Elemans explains. "Next to flight and echolocation, we now think that it is the buzzes powered by superfast muscle that allowed bats to better track the often erratic movements of insects in the dark and made them so successful," Ratcliffe concludes.
- C. P. H. Elemans, A. F. Mead, L. Jakobsen, J. M. Ratcliffe. Superfast Muscles Set Maximum Call Rate in Echolocating Bats. Science, 2011; 333 (6051): 1885 DOI: 10.1126/science.1207309
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