Mechanisms of American English Vowel Production in a Grey Parrot (Psittacus erithacus)

ABSTRAC.-Parrots are known for their capacity to reproduce the sounds of human speech, but few studies have investigated their mechanisms for producing such vocalizations. Using three methods of noninvasive video imaging (Super VHS video, infrared, X-ray radiography), we examined correlations between several elements of a Grey Parrot's (Psittacus erithacus) vocal-tract configuration and the bird's production of two vowels, /i/ ("eat") and /a/ ("rock"). This parrot uses mechanisms that both resemble and differ from those used by: (a) humans to produce English speech; and (b) some avian species to produce conspecific vocalizations. This Grey Parrot, for example, uses its vocal apparatus in some but not all of the ways used by humans to produce vowels. Although our Grey Parrot, like some oscines, appears to use beak opening to modify the characteristics of sound, the specific sound-modification properties of beak opening may or may not be similar to those of nonpsittacids. We describe a first-order model that, although simplistic, may aid our understanding of the mechanisms that enable a parrot to reproduce human speech. Received 5 December 1994, accepted 19 June 1995.