Object selection by head aim and acoustic gaze in the big brown bat

Abstract

Echolocating bats use their biosonar to locate, discriminate and capture their prey. Insectivorous bats face the additional challenge of tracking and pursuing a moving target. Often foraging in cluttered environments, these bats rely on head aim to determine their prey's location throughout an entire capture sequence. By directing their sound emission structures and acoustic gaze toward their target, bats keep prey in their acoustic field of view with the highest angular resolution and flattest incident sound spectrum. Although bats can perform head aim based tracking with an accuracy of a few degrees, acoustic tracking to such a degree would be unnecessary given the extremely broad beam widths. The likely explanation is that bats are not using conventional beam width as resolution and instead are performing spectral based pattern matching for localization. We investigated this strategy in a big brown bat (Eptesicus fuscus) using a 224 element microphone array. This array allows for fine scale, independent, variable frequency measurements of the beam with a high signal-to-noise ratio. Bats were trained to echolocate while remaining stationary of a platform. We recorded the beam pattern and head aim during echolocation to characterize the dynamics of echolocation.