Vocal performance during spontaneous song is equal in male and female European robins

The song of male birds is implicated in mate attraction and territory defence and assumed to evolve through sexual selection. Song production is hypothesized to represent a biomechanical challenge under physical, respiratory and neural limitation, leading to trade-offs. Although both sexes sing in numerous species, vocal performance has been little studied in females. European robins, Erithacus rubecula, of both sexes sing in autumn and winter to defend exclusive individual territories. We recorded robins singing spontaneously, that is, when not engaged in overt territorial interactions. We identified a trade-off be-tween two acoustic parameters: (1) the frequency ratio between successive song elements and (2) the duration of gaps between these elements. This trade-off might represent a vocal production limit. To compare vocal performance between the sexes we used two measures: vocal gap deviation (the dif-ference between how the bird sings and the theoretical performance maximum according to the putative vocal production limit we had identified) and sound density (the proportion of the song over which sound is present). Males and females did not differ in these two measures of vocal performance sug-gesting that the territory defence function of the song is used in social competition with members of either sex. In both sexes, vocal performance was not correlated with morphometric measures and repeatability coefficients were very small. Thus, vocal performance probably does not convey informa-tion about the signaller's body size or body condition, at least in spontaneous song of robins. These results inform the debate on selection forces driving female song.(c) 2022 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Automated summary

This study investigated the vocal performance of male and female European robins and found no significant differences between them. This suggests that song plays a similar role in territory defense and social competition for both sexes. Additionally, vocal performance was not correlated with morphometric measures or body condition.