Are good ornaments bad armaments? Male chaffinch perception of songs with varying flourish length

Birdsong functions as both a territorial and a mate-attracting signal, and is therefore subject to inter- and intrasexual selection through male-male competition and female mate choice. Consequently, differences in song perception between males and females could potentially lead to conflicting selection pressures on song structure. Chaffinch, Fringilla coelebs, songs have two distinctive parts: a series of rapidly repeated notes (the trill) followed by a sequence of more complex and often nonrepeated elements (the flourish). Males often spontaneously sing incomplete songs consisting mainly of the trill part, but their communicative function is unclear. We tested the reaction of males to songs with and without the terminal flourish in a dual speaker playback design by measuring their approach to the speakers. Like female chaffinches tested with the same stimuli in a previous study, males responded more to songs with both trill and flourish than to those consisting of a trill only. However, although females had preferred songs with a relatively longer flourish, males showed the strongest reaction (closest approach to the speaker) to songs with longer trills and shorter flourishes. The results suggest that males and females may perceive aspects of chaffinch song structure differently, in which case it could be under conflicting pressure of intra- and intersexual selection. (C) 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.