MOTOR CONSTRAINTS ON VOCAL DEVELOPMENT IN A SONGBIRD

The development and evolution of bird songs may be influenced by the m echanisms that underlie sound production, although the nature of this influence is not well understood. Here it is shown experimentally that vocal development in songbirds can be affected by physical limits on how birds are able to sing. Young swamp sparrows, Melospiza georgiana, were presented with conspecific song models modified such that rates of syllable repetition were increased above normal rates. Imitations o f these songs were inaccurate in ways that indicated motor constraints on vocal performance and that did not indicate perceptual or memory-b ased constraints. Some song imitations were deficient in trill tempo a nd/or syllable composition, and others were produced with a species-at ypical 'broken' syntax, in which pauses were interspersed within songs . These results illustrate how the development and evolution of trill structure can be limited by motor constraints on vocal production, and also identify a possible mechanism for the evolution of a novel form of song syntax. (C) 1996 The Association for the Study of Animal Behav iour.