These results together demonstrate that the costs of singing, as measured by their overall net effects on body reserves, can have a significant impact on the energetic state of daytime-singing birds.Ībstract Most bird species sing by day, with two distinct peaks of vocal activity-around sunrise and sunset. Our analyses suggested that this might have been due primarily to a reduction in food intake rate, rather than to the metabolic cost of the singing itself or a concurrent increase in locomotor costs. In all three parts of our study, birds gained less mass when they sang more. (iii) Manipulations of the song rate of aviary-housed robins using playbacks of conspecific song. (ii) Manipulations of the song rate of free-living robins using playbacks of conspecific song. In this paper we investigated the effect of variation in song rate on the body reserves of a typical daytimesinging bird, the European robin Erithacus rubecula, singing at different rates in three different circumstances: (i) Natural variation in song rate of free-living robins. However, it is not clear how such costs compare with those incurred by daytime-singing birds, which may forfeit foraging opportunities when they sing. Overnight loss of reserves has previously been found to increase with increasing song rates in nocturnally singing common nightingales Luscinia megarhynchos. Two potential costs are a metabolic cost of singing, and lost feeding opportunities, but such energetic costs will only be biologically important if they have a significant effect on the bird's body reserves. AbstractThe functions of bird song are well described, but empirical studies examining the costs of singing are scarce.
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