Terminal buzz gives bats their hunting edge

Bats owe their success to superfast muscles in their larynx, which allow them to make a series of rapid calls as they home in on insect prey. These calls are key to their ability to hunt at night ? something very few flying animals actually do.

Most bats navigate by echolocation. They produce a high-pitched call and listen for the echoes, which tell them how far away objects are and what they are. After a bat spots an insect it calls more frequently, eventually calling up to 160 times a second (160 Hertz) as it goes for the kill. This final sequence of calls has a rather appropriate name: the terminal buzz.

Calling faster means the bats get more information, but there has to be an upper limit, says Coen Elemans of the University of Southern Denmark in Odense. "It's the muscles that limit the rate," he says.

Elemans had previously shown that songbirds have superfast muscles, which control the pitch of their calls and enable them to sing complex songs. He has now found the same kind of muscles in the larynxes of Daubenton's bats (Myotis daubentoni).

Speedy bat

The bats' muscles are some of the fastest known to exist, able to contract and relax at frequencies up to 200 Hz. Human muscles barely manage 10 Hz, and even hummingbird wings can clock only around 40 Hz. However the superfast muscles of songbirds are the fastest, at around 250 Hz.

"When bats evolved around 50 million years ago, the skies were full of night-flying insects that nobody was eating," Elemans says. Echolocation by itself would not have been enough to hunt fast-moving insects in the dark, but the addition of superfast muscles and the terminal buzz could have given bats the advantage. "We think most bats that echolocate with their larynx probably have these muscles," Elemans says.

Echolocation is so crucial to bats' lifestyle that they probably evolved it before flight, says Brock Fenton of the University of Western Ontario in London, Canada. Without it, they would not have been able to prosper as nocturnal flying hunters.

That idea took a knock with the discovery in 2008 of a 52-million-year-old fossil bat that apparently flew without echolocation. Then, last year, Fenton took a closer look at the fossil and found evidence that it could indeed echolocate. He says well-preserved fossils should show clear traces of the superfast muscles, resolving the question once and for all.

Fenton says echolocation gives bats access to so many insects that they probably don't need to compete with each other for food. During a recent radio-tracking study he observed a 30-gram female bat leave her cave for just 20 minutes to hunt. "The next morning she produced about 5 grams of crap", around 17 per cent of her bodyweight, he says ? all from the insects she caught in those 20 minutes.

Journal reference: Science, DOI: 10.1126/science.1207309

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