The muscular, nimble tongue of parrots may help explain their uncanny ability to mimic human speech, scientists have concluded. The birds can modulate the sound coming from its voice box by adjusting their tongue--the only animal known to do this other than humans. Researchers believe the finding represents a new example of convergent evolution.
Birds and humans share the ability to make complex vocalizations. But what's different about humans is that their vocal tract filters the sound produced by the vocal cords, helping to enable speech. The vocal tract emphasizes certain pitches, called formants. That's the stuff of vowels. In addition, the tongue can change sounds by altering its shape and position.
By contrast, scientists thought bird vocalizations were modulated mainly by their sound-producing organ, the syrinx. But because parrots move their tongues when vocalizing, some scientists suspected that parrot tongues help create their oohs and aahs, as in humans. In the latest issue of Current Biology, neuroethologist Gabriël Beckers of Leiden University in the Netherlands and colleagues at Indiana University, Bloomington, set out to test this idea in Monk parakeets, Myiopsitta monachus.To do so, the team experimented with five dead Monk parakeets. First, the scientists removed the animals' syrinx and replaced each one with a small speaker, which they attached to the vocal tract. Then they recorded what came out of the beak while holding the tongue in various positions. The sound was clearly louder at certain pitches, a sign of formants. Moreover, repositioning the tongue altered the pitch and loudness of the formants. That's analogous to the way people talk, Beckers says. Formants help parakeets mimic human speech, and formant-like patterns are also found in parakeet calls, suggesting that their real role is in chatting with one another. This suggests that use of the tongue in vocalizations evolved at least twice, the researchers say.By clarifying how parrots make sounds, the study tackles the "key first issue" in studying vocal imitation, says bioacoustics expert Tecumseh Fitch of the University of St. Andrews in Fife, U.K. The fundamental issue, he adds, is what's going on in the parrot's brain.Related sites
Gabriël Beckers' home page
Background on formants
Information on parrots