Male song of a promiscuous bird without paternal care is more complex than previously thought

Abstract

Abstract The Aquatic Warbler is one of the rarest European passerines, characterised by promiscuity, lack of pair-bonds and female-only parental care. This makes the species an important model for studying the function of avian courtship song. The song of the Aquatic Warbler consists of whistle and rattle phrases produced as discontinuous A-, B- and C-songs, which are built by a single rattle, a rattle and a whistle, and more than two rattle-whistle phrases, respectively. The A- and B-songs are aggressive signals in male-male interactions, while C-songs are important for female choice. Here, we analysed recordings of 40 individually marked males, and determined the enumerated and estimated repertoire size. The males sung 16–158 (mean 99) different phrases. The estimated repertoire size ranged between 18 and 300 (mean 155) and was significantly predicted by the number of C-songs. The rattle repertoire was larger than the whistle repertoire and both positively correlated with the number of C-songs. Our study indicates that in the Aquatic Warbler, the repertoire size is greater than previously believed, and the courtship song is flexible and efficient, enabling both female attraction through quick presentation of large repertoires, and rival deterrence through production of many short and simple A-and B-songs.