Echolocation at high intensity imposes metabolic costs on flying bats.

The costs of echolocation during flight were thought to be negligible for bats, but here it is shown that this is true only below a certain intensity threshold. Above 130 dB, the costs of sound production become too expensive for small bats. Vocalizations are of pivotal importance for many animals, yet sound propagation in air is severely limited. To expand their vocalization range, animals can produce high-intensity sounds, which can come at high energetic costs. High-intensity echolocation is thought to have evolved in bats because the costs of calling are reported to be negligible during flight. By comparing the metabolic rates of flying bats calling at varying intensities, we show that this is true only for low call intensities. Our results demonstrate that above 130 dB sound pressure level (SPL, at a reference distance of 10 cm), the costs of sound production become exorbitantly expensive for small bats, placing a limitation on the intensity at which they can call.