Song syllable variation tolerance and motor theory of song perception: the territorial reaction of cirl bunting Emberiza cirlus to homologue syllables.

The extent of syllable variation tolerance was tested using synthetic homologue syllables. A synthetic copy of a common syllable type of cirl bunting Emberiza cirlus song was used as control. Homologue syllables, in the same frequency range but shorter or longer, were created by multiplying (2/3, 5/3, 7/3) the time scale of the control syllable. By this way the specificity of homologue syllables inside (2/3) and outside (5/3 and 7/3) the syllable duration range (mean ± 2 SD) of the species were tested. Results do not support a hypothesis for syllable variation tolerance founded on motor perception theory. Processes free from production occur in syllable recognition.