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RETURN TO THE WORLD SCIENCE HOME PAGE Secret of parrots' talking ability revealedPosted
Sept.
7,
2004
Scientists say they have learned part of the secret of parrots' remarkable ability to talk: like humans, they use their tongues to shape sound. Most bird species weren't previously known to do this. "Control of tongue movements is an important part of [parrot] communication, just as it is in humans," said Roderick Suthers of Indiana University at Bloomington, who participated in the research. Most birds were previously thought to rely only on a sound-making organ called the sirinx, above the lungs, to produce sound. Researchers and bird enthusiasts have long noticed that parrots bob their tongues back and forth while they vocalize, but it wasn't known whether the tongue motions contributed significantly to sound-making. The report by Suthers and biologists Gabriel Beckers and Brian Nelson in the Sept. 7 issue of the research journal Current Biology shows that even tiny changes in the position of a parrot's tongue can lead to big differences in sound. Bird song is an close analogue of human speech and can be studied to understand how communicative abilities develop, Beckers said. "Song is something that has to be learned, and it can only be learned by listening. Very specific areas of the bird's brain aid song and imitation. Humans have language centers. Before, we used to think all the complexity of parrot communication was because of the syrinx. Now we think it's likely the tongue is involved, just like with human speech." Beckers, the study's lead author, is now a research fellow at Leiden University in the Netherlands. The scientists used five monk parakeets, small parrots native to South America. While a speaker swept through a series of tones, from 500 to 11,000 Hz (from the B above a piano's middle C to a high-pitched F beyond the keyboard's range), the researchers measured how much the birds' tongue position influenced the outgoing sound. They found that a change of just a fraction of a millimeter in tongue position could significantly affect the qualities of the emerging sound. "By analogy, it's larger than the difference between an A and an O in human speech," Beckers said. The scientists also believe they are the first to identify four acoustic "formants" in parakeet sounds. Formants are small ranges of frequencies that remain strongly audible as sound travels past the throat, tongue, mouth and nasal cavities. The geometry of these passages deadens some frequencies but leaves others relatively unaffected. What's left distinguishes the character of a sound -- in this case, the voice of a parakeet. Human voices also have formants. Because of differences in genetics, development and behavior, these fingerprint-like formants vary greatly from individual to individual. By studying parrots, Beckers, Suthers and Nelson hope to learn more about what structures are responsible for that variation in both birds and humans. * * * * * Send us a comment about this story
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