The costs of singing in nightingales

The costs of singing in birds are poorly understood. One potential type of cost is a metabolic cost of singing. Previous studies have measured short-term changes in oxygen consumption associated with bouts of vocalizations, with equivocal results. In this study, I used an alternative approach to measuring the metabolic cost of singing, by measuring overnight loss of body mass, in male common nightingales, Luscinia megarhynchos, singing at night at different rates. Nightingales were shown not to forage at night. They reached a higher mass at dusk prior to singing more at night, and lost more mass overnight when dusk mass and overnight song rate were high. These results show that singing at night is associated with increased overnight consumption of body reserves, which represents a significant metabolic cost of singing at night. However, the correlation between dusk mass and overnight song rate makes it impossible to determine whether these costs arise from the energetic costs of the singing itself, or from the metabolic costs of the additional body reserves laid down at dusk on nights when song rate was high. There are also likely to be costs associated with accumulating and carrying these extra body reserves during daylight, as well as other potential costs of singing such as an increased risk of predation. These results are consistent with those models of signalling in biology that predict or assume that honest signals are costly. (C) 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.