Disentangling Relations among Repertoire Size, Song Rate, Signal Redundancy and Ambient Noise Level in European Songbird

The majority of male songbirds have small repertoires and sing with eventual variety; that is, they present one song type several times before switching to the next one. Several hypotheses have been proposed to explain this phenomenon. The antiexhaustion hypothesis argues that song-type switching prevents muscle fatigue in the syrinx. The signal redundancy hypothesis suggests that repeating the same signal increases transmission success. Here, we have studied the song behaviour of the chaffinch, Fringilla coelebs, a common Eurasian species in which the males sing a few different song types and provide eventual variety. We tested different hypotheses to explain the temporal organisation of song output (repertoire size, song rate, bout duration, etc.) as a function of ambient noise by comparing birds from the same macrogeographic region in which the birds live either in a noisy town (n = 71) or in a quieter forest habitat (n = 68). Contrary to the prediction of the signal redundancy hypothesis and the results of earlier work on chaffinches living close to noisy streams, we found no significant differences in song characteristics between the town and forest populations. Our results support the antiexhaustion hypothesis because males with larger repertoires were able to sing with a significantly higher rate due to faster switching between different song types and producing shorter bouts. Sample size or population differences between our study and earlier investigations of the same species may explain the inconsistency with previous findings. Future studies should focus on determining the relations between song organisation and the directly measured quality of males and females' choice using, preferably, a longitudinal approach.