What is the whistle all about? A study on whistle songs, related male characteristics, and female song preferences in common nightingales

In many passerine species certain song structures have evolved to convey information to conspecific males or females. For example, in the common nightingale Luscinia megarhynchos, the ‘whistle part’ is a striking acoustic feature of some song types. Whistle songs have been suspected to be particularly well suited to attract females and/or to be important during female choice, but this has never been tested directly. In this study, we used a two-pronged approach for addressing the function of whistle songs in intersexual communication. First, we analysed relationships between whistle song features and male characteristics reflecting overall male quality. We found that the number of whistle songs produced and acoustic consistency of single whistle elements predicted male body measures, i.e., males who sang more whistle songs were heavier and larger, and produced whistle elements with higher consistency. Second, we conducted playback experiments with females either with or without whistle songs. Females responded more strongly to whistle songs by moving and vocalizing more during the whistle playback. We conclude that whistle songs might play an important role in nightingale mating, as they evoke high arousal in females, and different whistle song features may signal different aspects of male quality to females.