Singing is not energetically demanding for pied flycatchers, Ficedula hypoleuca

Male passerine bird song is a classic example of a sexually selected display. Theory predicts that such displays should be costly, but there are few empirical data on the potential costs of bird song. We measured the rate of oxygen consumption by male pied flycatchers, Ficedula hypoleuca, singing inside a respirometry chamber. Song is known to be important in mate choice by pied flycatchers, so we predicted that if passerine song is energetically costly, we should be able to measure the costs in this species. The metabolic rate of singing pied flycatchers (N=3) was 0.62+/-0.11 W, which was equivalent to 2.7+/-0.5 x basal metabolic rate. Metabolism during singing did not differ significantly from that during standing. A power analysis of this test showed that the metabolic rate of singing birds was less than 1.12+/-0.04 times that of standing birds. Comparing the maximum cost of song production with daily energy expenditure (DEE) during nestling rearing, each hour of singing rather than standing would increase DEE by 0.4%. Thus, song production appears to be energetically cheap in the pied flycatcher in relation to the overall daily energy budget. However, because birds cannot sing and eat at the same time, there could be an energetic constraint to song duration owing to the need to spend sufficient time foraging.