Energetic cost of calling: general constraints and species-specific differences.

The energetic cost of acoustic signalling varies tremendously among species. Understanding factors responsible for this heterogeneity is important for understanding the costs and benefits of signalling. Here, we present a general model, based on well-established principles of bioenergetics, which predicts the energetic cost of call production across species. We test model predictions using an extensive database of resting and calling metabolic rates of insects, amphibians and birds. Results are largely supportive of model predictions. Calling metabolic rates scale predictably with body mass and temperature such that calling and resting metabolic rates are directly proportional to each other. The cost of acoustic signalling is approximately 8 times higher than resting metabolic rate in ectotherms, and approximately 2 times higher in birds. Differences in the increase in metabolic rate during calling are explained by the relative size of species' sound-producing muscles. Combined with published work, we quantify call efficiency and discuss model implications.