Echolocation call frequencies of bats vary with body temperature and weather conditions

Many animals vary their acoustic signals with weather conditions to ensure sufficient range of signal transmission as atmospheric attenuation increases (the atmospheric attenuation change hypothesis). However, few studies have considered the effects of weather conditions on the vocalizations of endotherms via the effects on their physiological condition (the physiological change hypothesis). In the present study, we directly linked weather conditions to changes in bats' body temperatures and to their echolocation call frequencies. We found a significantly positive correlation between body temperatures and call frequencies among individuals of the great leaf-nosed bat, Hipposideros armiger, in the wild. We then monitored changes in body temperature and call frequency of H. armiger over an hour at an ambient temperature of about 11 degrees C. The bats emitted echolocation calls of lower frequencies with decreasing body temperature caused by decreased ambient temperature, supporting the physiological change hypothesis. We also investigated changes in body temperature and echolocation call frequencies for H. armiger from summer to winter. The bats' body temperatures decreased with decreasing ambient temperature. However, echolocation call frequencies increased significantly. A linear mixed-effects model suggested that the change in atmospheric attenuation rather than body temperature had a significant effect on the call frequency, supporting the atmospheric attenuation change hypothesis. Overall, our results suggested that weather conditions can affect the echolocation signals of bats via the effects on their body temperature and on atmospheric attenuation. When both effects coexist, weather-induced adjustments in the echolocation signals could be more likely to be driven by the atmospheric attenuation effect. (c) 2021 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.