Reed bunting (Emberiza schoeniclus) males sing an 'all-clear' signal to their incubating females

Abstract

AbstractWhile sexual functions of birdsong have been intensively investigated, non-sexual functions have received less attention. After pair formation males may sing to communicate with their established mates. Song aimed at incubating and feeding females could serve as an 'all-clear' signal, showing that there is no risk of predation and that it is safe for the female to exit the nest or to feed the young. Females should therefore preferentially leave nests when mates are singing nearby. Additionally, a vigilant male near the nest site could protect the brood from potential risks like predation and females could stay away longer for foraging. In this study, we investigated aspects of male singing activity of reed buntings (Emberiza schoeniclus) during incubation and feeding of nestlings after pair formation. Exits of incubating females from the nest occurred significantly more often than expected during male song output. When their mates were singing at high rates, females stayed away longer for incubation breaks. During the nestling period we found a high variation in male song output. Males that sang more fed their young significantly less. This suggests that time devoted to singing limits other activities such as feeding of offspring. Male reed buntings could choose different strategies for paternal investment: They either feed at high rates or they sing more to signal their vigilance. Another reason for this trade-off might be a conflict between paternal investment and territory defence or extrapair behaviour. However, even if male song after pairing has additional sexual functions, we suggest that non-sexually selected functions may be more common than expected.