Manipulating Environmental Clutter Reveals Dynamic Active Sensing Strategies in Big Brown Bats

Abstract

Vocalizing animals confront acoustically challenging conditions in which background noise (clutter) can mask or shift attention away from biologically relevant signals. Echolocating big brown bats (Eptesicus fuscus) are excellent comparative models for studying how animals differentiate between multiple sound sources in complex acoustic scenes. We trained four big brown bats to fly down an asymmetrical corridor producing distinct clutter echoes from the two sides. While in flight, they were presented with playbacks of exemplars of an echolocation call, a social communication call, or waterfall noise, from one or both sides of this corridor; a silence condition served as a control. We predicted that bats would perceive the playbacks, as indexed by modifications of their vocalizations and shifts in their head aim. Bats completed flights at a high rate of success in all conditions. Although bats produced calls in similar sized sonar sound groups in playback and silent trials, they emitted more echolocation calls and shortened the time intervals between calls in response to playbacks. These comparisons suggest the playbacks increased the perceptual difficulty of the task to some extent. Bats aimed their heads towards the left side of the corridor where clutter echoes were acoustically stronger but also sparser. Changes in head aim in response to playbacks were small. Our data suggest that big brown bats flying through clutter detect differences in the information content of surrounding acoustic scenes and alter their echolocation behavior accordingly.