Temporal variation in chaffinch Fringilla coelebs song: interrelations between the trill and flourish

The description of within-population variation of a signal is an important first step when studying its communicative function. In chaffinches Fringilla coelebs all song types consist of two structurally different parts: the trill (a series of two to five phrases of repeated syllables) followed by a more complex end phrase, the so-called flourish (a shorter sequence of mostly non-repeated syllables). The relative durations of the two song parts have been reported to affect male and female responses in playback studies. While this suggests a communicative function of relative trill and flourish duration, within-population variation of these parameters has not yet been quantified. We recorded 3084 songs of 108 different song types from 79 individuals and measured the song, trill and flourish duration. This revealed substantial variation in duration of the two main song parts. An analysis of the variance components showed that trill duration was more variable within song types and between birds than flourish duration, but less variable between song types. Moreover, the more different phrases there were in the trill, the longer was its duration. There was more variation in trill duration within song types with relatively short flourishes. Possible communicative functions of the observed variation are discussed in the light of previous evidence from playback experiments.