Echolocating bats modify biosonar emissions when avoiding obstacles during difficult navigation tasks

Abstract

Big brown bats modulate their biosonar emissions in both time and frequency when flying through acoustically cluttered environments. We challenged single bats or bats in pairs to fly along a narrow U-shaped corridor 7 m in path length formed by rows of vertical plastic chains, while also avoiding additional interspersed horizontal chains. Bats emitted calls in complex sonar sound groups in all flight conditions. When no added horizontal obstacles were present, each bat’s flight success rates averaged 80%; introducing horizontal obstacles decreased success rates to 45-65%, with little improvement over several days. When two bats flew simultaneously from opposite ends of the U-shaped path, they rarely collided, instead swerving closely past or keeping farther apart in elevation. They increased call rate and call amplitude, while decreasing terminal FM broadcast frequency, as they approached near the middle of the U-shaped path. Increases in call amplitude persisted throughout the remainder of the flight while call rate and terminal frequency returned to baseline levels. These data show the limits of call modifications during difficult maneuvers in dynamic conditions. They demonstrate the bat’s effective awareness not only of the continuously distributed clutter but also of another, moving bat. [Work supported by ONR.]