Thermal energetics of male courtship song in a lek-breeding bat

The use of songs for mate-attraction is common. Intensive songs may indicate high energetic investment, reflecting an individual’s resource-holding potential and attractiveness as a prospective mate. Consequently, there can be a direct relationship between song metrics and lifetime reproductive success. While singing is held to be energetically costly, quantitative studies in mammals are lacking. Here, we present an exploratory analysis of energetic costs in a singing bat ( Mystacina tuberculata ). We recorded the songs of 12 male bats and quantified skin temperature ( T sk ) responses using temperature telemetry to estimate energy expenditure. We hypothesised that singing would be energetically costly and predicted correlations between T sk and song duty cycle and between duty cycle and body size. Contrary to our expectations, we found estimated energetic expenditure while singing to be comparatively low. We also found no relationship between estimated energy expenditure and duty cycle, and neither estimated energy expenditure nor duty cycle was correlated with body size. Our results suggest that energetic costs of singing in bats may be lower than previously assumed, and that song output may convey only limited fitness information. Significance statement Song is commonly used to communicate information related to mate-attraction or territory defence. Some aspects of song production require more energy to produce, making them an honest signal of a singer’s investment. While our knowledge of bird song and its relationship to mating success is well developed, a similar understanding regarding mammalian song is severely lacking. Numerous bat species produce song, yet we know little about the energetics of song production in this large and diverse order. Using temperature telemetry, we estimate the costs of singing in a free-living lek-breeding bat. To our knowledge, this is the first study to estimate the energetic costs of song production in a mammal.