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Fastest Known Muscles Found in Songbirds' Throats

Matt Kaplan
for National Geographic News
July 10, 2008
 
The fastest muscles known lie within the throats of songbirds, according to new research on how birds vibrate their vocal cords.

Experts have long wondered whether bird song is caused by passive interactions as air moves between the vocal muscles or direct neuromuscular control.

"I had been looking at the muscles in a pigeon species and was amazed by how fast they were moving," said lead study author Coen Elemans at the University of Utah in Salt Lake City.

"[Pigeons] have really boring, slow songs, and it made me wonder what the muscles in songbirds were like, so I decided to find out."

What Elemans and colleagues discovered is that zebra finches and European starlings can change their tunes at frequencies as high as 250 hertz via direct muscle control.

This means that they are moving their muscles a hundred times faster than a blink of the human eye.

(Related story: "Salamander Tongue Is World's Most Explosive Muscle" [March 9, 2007].)

The research is described this week in the journal PLoS One.

Fast Twitch

To find out how songbirds make their quick-fire modulations, the researchers first measured muscle activity in freely singing starlings and found that muscle motion corresponded to changes in song tone.

The team then exposed vocal muscle fibers from starlings and zebra finches to electrical stimulation in the lab to see just how fast the muscles can expand and contract.

The vocal muscles of male and female starlings both conntracted at about 3.2 milliseconds. Male zebra finch muscles, meanwhile, twitched at roughly 3.7 milliseconds while females' moved at 7.1.

Tiny twitching muscles on either side of rattlesnake rattles, along with muscles in the swim bladders of some fish, have been recorded approaching these speeds. (See photos of rattlesnakes in action.)

But Elemans's team concludes that songbird vocal cords move faster than any muscle in any other known vertebrate.

Since most songbirds have the same general type of vocal cords, the discovery could mean that extremely fast-moving muscles are more common in nature than was previously thought.

Synchronized Chorus

Daniel Margoliash, a biologist at the University of Chicago who was not involved with the study, called the paper "as elegant as it is exciting."

"We've been fascinated by bird songs for so long, and this gives us a very important insight into the vocal organs behind them," he said.

"We had no idea muscles could work at these superfast rates," he added. "That they can and do is just amazing."

Daniel Mennill, an avian biologist at the University of Windsor in Canada, noted that fieldwork has shown songbird vocalizations to be among the most precisely timed behaviors in the animal kingdom.

"The synchronized duets and choruses of wrens, for example, are the most highly coordinated animal behaviors ever recorded," he said.

"These [new] results explain a lot about how birds actually achieve such amazing technical feats."

Study leader Elemans said he is keen to continue his search for creatures with superfast muscles, and he thinks bats will be good candidates.

"Bats echolocate with an auditory sweep that rapidly moves from very high pitch to very low," he said.

"I'm convinced that there are fast-moving muscles behind this sonic sweep."
 

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