Dynamic Echo Information Guides Flight in the Big Brown Bat

Abstract

Animals rely on sensory feedback from their environment to guide locomotion. For instance, visually guided animals use patterns of optic flow to control their velocity and to estimate their distance to objects (e.g., Srinivasan et al., 1991, 1996). In this study, we investigated how acoustic information guides locomotion of animals that use hearing as a primary sensory modality to orient and navigate in the dark, where visual information is unavailable. We studied flight and echolocation behaviors of big brown bats as they flew under infrared illumination through a corridor with walls constructed from a series of individual vertical wooden poles. The spacing between poles on opposite walls of the corridor was experimentally manipulated to create dense/sparse and balanced/imbalanced spatial structure. The bats’ flight trajectories and echolocation signals were recorded with high-speed infrared motion-capture cameras and ultrasound microphones, respectively. As bats flew through the corridor, successive biosonar emissions returned cascades of echoes from the walls of the corridor. The bats flew through the center of the corridor when the pole spacing on opposite walls was balanced and closer to the side with wider pole spacing when opposite walls had an imbalanced density. Moreover, bats produced shorter duration echolocation calls when they flew through corridors with smaller spacing between poles, suggesting that clutter density influences features of the bat’s sonar signals. Flight speed and echolocation call rate did not, however, vary with dense and sparse spacing between the poles forming the corridor walls. Overall, these data demonstrate that bats adapt their flight and echolocation behavior dynamically when flying through acoustically complex environments.

Echo-acoustic and optic flow interact in bats

“…5). This observation is consistent with previous observations that bats do not adjust flight velocity to the strength of echo-acoustic flow (Kugler et al, 2016;Warnecke et al, 2016).…”

“…Experimental and theoretical work has provided evidence that bats respond to echo-acoustic flow (Kugler et al, 2016;Lee et al, 1992;Müller and Schnitzler, 1999;Warnecke et al, 2018aWarnecke et al, , 2016. Although explicit information about the distance of objects is provided by echolocation through the delay between call emission and echo arrival time (Simmons, 1971), echo-acoustic flow is used to adjust the lateral distance along structured surfaces (Kugler et al, 2016;Warnecke et al, 2016). This behaviour is often observed, for example, in bats following the edges of vegetation in commuting flight (Holderied et al, 2006).…”

Sensing in a noisy world: lessons from auditory specialists, echolocating bats

“…The degree and direction of the shift depended on the sequence of pulses and echoes that were presented. This, and other recent neurophysiological (Beetz et al, 2016) and behavioral studies (Kugler et al, 2016;Warnecke et al, 2016), shows that bats are specialized for integrating the flow of echoes as they return from multiple sonar pulses.…”

Echo interval and not echo intensity drives bat flight behavior in structured corridors

“…Previous research has shown that echolocating bats navigate densely cluttered spaces with ease, adapting their flight and echolocation signal design to optimize information extracted from complex echo soundscapes (Falk et al, 2014(Falk et al, , 2015Hiryu et al, 2010;Petrites et al, 2009;Warnecke et al, 2016;Wheeler et al, 2016). Most studies investigating the bat's behavior in complex environments have challenged the animal to maneuver around obstacles that reflect uncontrolled echo-acoustic variables, which are difficult to quantify across individual subjects and trials (e.g.…”

“…Moss et al, 2014). Recently, we attempted to address this limitation by studying the bat's echolocation and flight behavior in an experimentally controlled corridor, in which we systematically manipulated echo-acoustic information (Warnecke et al, 2016). Specifically, we quantified the echolocating bat's flight trajectory and timing of biosonar signals in response to different echo flow patterns.…”