Female Pied Flycatchers <i>Ficedula hypoleuca</i> Can Discriminate Between Songs of Unmated and Mated Males and Avoid Being Deceived Into Polygyny

ABSTRACT A classic conflict of interest between the sexes occurs when males benefit from polygynous mating whereas females benefit from monopolising male parental care. In the pied flycatcher Ficedula hypoleuca , some males are polyterritorial, establishing a second territory far away from the first to attract a second female, apparently to deceive females into polygyny. Here, we focus on male song, addressing both the sender's and the receiver's perspective. We show that the individual males were singing shorter song strophes and increasing the syllable switching after they had become mated and were trying to attract a second female on a secondary territory. Thus, prospecting females may assess a male's mating status from his song. This was supported in mate choice experiments in large, outdoor aviaries where the songs from unmated and already‐mated males on secondary territories were broadcasted. The females spent most time with the male in the compartment where the song of an unmated male was broadcasted. However, this differential female response in favour of the song from an unmated male disappeared when the syllable switches of the broadcasted songs of the males were manipulated to resemble the song of a mated male. We suggest that an increased syllable switching between songs of mated males can be related to constraints of defending separate territories towards male intruders, including male neighbours and prospecting males. This is important because competition for suitable nest sites may be strong and because polyterritorial males must return frequently to the first territory to keep the nest site and the first female. Prospecting females may take advantage of the information from the song to assess male mating status and thereby avoid being deceived into polygyny.