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.
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