"We show that songbirds adjust the size and shape of their vocal tract to 'fit' the changing frequency of their song," IU neurobiologist Roderick Suthers said. "This enables the bird to produce a more whistle-like, pure-tone song."
The finding supports a growing consensus that birds and humans make sound in much the same way -- although it is presumed these processes evolved independently of each other in birds and hominids. In 2004, Suthers reported in the journal Current Biology that monk parakeets use their tongues to shape sound. Other studies have implicated beaks, especially beak gape, in shaping the sound that birds produce. Similarly, humans move their tongues, alter the shape of their upper vocal tracts, and change the shape of their mouths when they sing, laugh, talk and groan.
"The bird's vocal tract, like the human vocal tract in speech, acts as a resonance filter that can control the sound coming from the mouth," Suthers said. "Beak movements during song also contribute to this filter, but are not as important as changes in the size of the internal vocal tract. Human sopranos use the same technique as the cardinal to increase the loudness of very high notes so they can be heard above the orchestra."
That birds' throats vibrate when they sing will come as no surprise to birdwatchers. The effect of these oscillations on the birds' sound production, however, was unknown.
The acoustics of sound-making are complicated. Most tones produced in nature are accompanied by a complex series of higher-pitched, quieter tones called overton
Contact: David Bricker