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Non‐Vocal Shaping of Avian Song Development: Parallels to Human Speech Development

Vocal development in young male cowbirds (Molothrus ater) is sensitive to acoustical stimulation from males, but also to social feedback from female cowbirds, even though females do not sing. Juvenile males show different vocal trajectories if housed with local or distant population females. The major goal of the present study was to identify differences in the form and timing of non-vocal cues from females during the period in early spring when juvenile males begin to sing stereotyped song and to finalize their repertoires. We housed juvenile males with either local or distant population females and no adult males. We found significant differences between the two groups of females in the use of wing stroking and in male reactions to wing strokes and gapes. There were also differences between the groups in male song performance. To understand further the potential consequences of these differences, we correlated measures of male and female responsiveness to results reported in Smith et al. (2000) on vocal ontogeny and song potency. We found that wing stroking by females was associated with a faster rate of song development and tended to relate to differences in song potency. The non-vocal shaping seen here may represent a general mechanism for the development of vocal communication, as similar processes influence phonological development in human infants.