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. oder aber gar keine Pfeifstrophen enthielten. Dabei reagierten die Weibchen eindeutig stärker auf die Gesänge mit hohem Pfeifstrophenanteil. Aufgrund dieser Befunde kommen wir zu der Schlussfolgerung, dass der Pfeifstrophengesang der Nachtigall in der Tat eine wichtige Rolle in Verpaarungskontexten übernimmt, da er zum einen stimulierend auf die Weibchen wirkt und zum anderen als Indikator für diverse Qualitätsaspekte der Männchen fungieren kann.

BackgroundSexual ornamentation may be related to the degree of paternal care and the ‘good-parent’ model predicts that male secondary characters honestly advertise paternal investment. In most birds, males are involved in bringing up the young and successful reproduction highly depends on male contribution during breeding. In passerines, male song is indicative of male attributes and for few species it has been shown that song features also signal paternal investment to females. Males of nightingales Luscinia megarhynchos are famous for their elaborate singing but so far there is only little knowledge on the role of male song in intersexual communication, and it is unknown whether male song predicts male parenting abilities.ResultsUsing RFID technology to record male feeding visits to the nest, we found that nightingale males substantially contribute to chick feeding. Also, we analyzed male nocturnal song with focus on song features that have been shown to signal male quality before. We found that several song features, namely measures of song complexity and song sequencing, were correlated with male feeding rates. Moreover, the combination of these song features had strong predictive power for male contribution to nestling feeding.ConclusionsSince male nightingales are involved in chick rearing, paternal investment might be a crucial variable for female mate choice in this species. Females may assess future paternal care on the basis of song features identified in our study and thus these features may have evolved to signal direct benefits to females. Additionally we underline the importance of multiple acoustic cues for female mating decisions especially in species with complex song such as the nightingale.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0390-5) contains supplementary material, which is available to authorized users.

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Male songbirds often maintain territories throughout the breeding season, and one of the main functions of song is to deter invaders. Therefore, the distance of an unknown singing rival should play a crucial role within territorial singing interactions of males. This distance is expected to be assessed as more threatening the closer the rival approaches. Here, we tested this assumption by conducting nocturnal playbacks from two different distances in territorial Common nightingales (Luscinia megarhynchos). Immediate vocal responses of birds were examined by analysing changes in song structure as well as temporal response features. The next morning, follow‐up playbacks from an intermediate distance allowed us to investigate longer‐lasting effects of nocturnal playbacks. We found that the distance of a simulated rival had an effect on both immediate and later vocal responses of territorial male nightingales with different song parameters being affected during nocturnal and diurnal singing. This indicates that birds perceive intruder distances and adjust their response behaviour both immediately and in later interactions.

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