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.