Parrots can shape sound with their tongues.© Kathleen CarrEver wondered what makes parrots so good at mimicking human speech? It turns out that the feathered impressionists use their tongues to create vowel-like sounds, just as we do.
In human speech, noise is produced in the larynx and can then be modified by the movement of the tongue in the mouth. This helps us to make complex vowel and consonant sounds.
Until now, many researchers thought that birds produced and modified their song in the avian equivalent of the larynx, the syrinx, and that the tongue played no role at all.
But parrots are known to bob their fleshy tongues back and forth when they talk, so Gabriel Beckers from Leiden University in the Netherlands and colleagues decided to see whether these movements contribute to the birds' great talent for mimicry. Their results are published in Current Biology1.
The team studied five feral monk parakeets (Myiopsitta monachus), which had been caught and killed as part of a government pest control program in Florida. In each bird, they replaced the syrinx with a tiny electronic speaker and then used a hook to move the tongue around as the amplifier played bursts of sound.
Tongue movements of less than a millimetre made a big difference to the quality of emerging vowel-like sounds, called formants, the team found. "It is larger than the difference between an 'a' and an 'o' in human speech," says Beckers.
Beckers thinks that the birds' ability to manipulate their tongues to articulate vowel sounds probably underpins their talent as impersonators.
Look who's talking
Parrots are likely to use these sounds in natural communication, says Irene Pepperberg from the Massachusetts Institute of Technology, who studies bird vocalizations. "Subtle differences in sound are very important to these birds," she says.
Male songbirds, for example, tend to sing only at certain times of the year and for a specific reason: to attract females. But male and female parrots communicate all the time, says Pepperberg. They probably use formants and other vocalizations to convey complicated information, such as individual identity and predator threats.
The discovery "suggests that parrot communication may be more complex than we thought", says Beckers.
Pepperberg has first-hand experience in this area. Her team has studied an African Grey parrot, called Alex, in the lab for 27 years. Alex can articulate sounds for objects, shapes, colours and materials, knows the concepts of same and different, and bosses around lab assistants in order to modify his environment.
Pepperberg claims that the ability to form vowel-like sounds is no accident. She says that it contributes to the richness of parrot 'language'.
The recent study suggests that the ability to produce formants evolved at least twice, once in parrots and once in humans, says Beckers. Tongue articulation gives an extra dimension to vocal complexity, a phenomenon that must have proved useful to both species.
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