By Susan Milius
The power behind a ring dove’s trill belongs to the fastest class of vertebrate muscles known, reports a team of physiologists. This is the first demonstration of superfast muscles in a bird, the researchers say.
These muscles contract some 10 times as fast as the muscles that vertebrates typically use for running, says Coen Elemans of Wageningen University in the Netherlands. Concentrations of such high-speed tissue also occur in the rattlesnake’s tail and the toadfish’s swim bladder, which the fish uses to produce sound. Some vertebrates’ jaw and eye muscles have superfast fibers, but these muscles are slower than the superfast snake and fish muscles.
Elemans says that a dove’s trill, although fast, isn’t particularly fancy as birdsongs go. If people examine other birds’ vocal muscles, they are likely to find other examples of superfast contractions. “It’s probably all around us,” says Elemans.
Birdsong specialist Carel ten Cate of Leiden University in the Netherlands takes a similar viewpoint. He says that despite the known differences among birds’ muscle arrangements, “it would be surprising if it was only in the dove group that they evolved to become very fast.”
Elemans points out that people for centuries have been looking for the mechanisms behind birdsongs but that recent electronic and physiological advances have opened new frontiers. In the Sept. 9 Nature, he and his colleagues report on studies of ring doves (Streptopelia risoria), an African species domesticated by hobbyists.
Elemans and one of his coauthors, Franz Goller of the University of Utah in Salt Lake City, surgically implanted tiny electrodes into a bird’s sound-production system. The electrodes gave a rough indication of when particular muscles were active. The researchers found the muscles that contract repeatedly during cooing.
Those muscles control membranes located just above the junction where the bronchial airways from the lungs combine to form the trachea. To coo, the dove sends air up from its lungs and past the membranes, which then vibrate. The tension and position of the membranes determine the quality of the sound. The researchers propose that a coo’s rapid trill, clocked at 30 repetitions per second, requires fast muscle action.
For further testing, Elemans and his colleagues removed the pair of muscles that controls the membrane. In a laboratory setup, the muscles contracted and partly relaxed in just 9 to 10 milliseconds. A typical vertebrate’s locomotor muscle needs at least 100 milliseconds to contract.
Neurophysiologist Roderick Suthers of Indiana University in Bloomington says the paper “puts a new perspective” on the study of birdsongs. Song centers in bird brains have attracted much interest, but there’s been less attention to the vocal muscles.
Suthers suggests that researchers examine the muscles of songbirds, which have more-complex songs than doves do. A typical songbird’s vocal apparatus has two independent parts.
