The effect of mouth gape angle on beam size for echolocating Eptesicus fuscus

Abstract

The sonar beamwidth of mouth-emitting echolocating bats is hypothesized to change according to mouth gape angle, with a narrowing of the beam predicted with wider mouth openings. To investigate the relationship between mouth gape angle and beam size, we recorded both the emitted sonar beam as well as the mouth opening for four bats during a target detection task. Sonar signals were recorded with an array of microphones, and bat mouth dynamics was recorded with an action camera recording at 240 frames per second. The video frames corresponding to each pulse emission were extracted and the mouth gape angle was measured. Sound intensity, −3 dB beam angle, and frequency characteristics were calculated from the microphone array and compared to the mouth gape angles to determine the influence of mouth opening on echolocation signals.