Modulation of acoustic navigation behaviour by spatial learning in the echolocating bat Rhinolophus ferrumequinum nippon

Yasufumi Yamada,Shizuko Hiryu,Yuya Yamamoto,Kentaro Ito,Yurina Mibe,Olga Heim

doi:10.1038/s41598-020-67470-z

Yasufumi Yamada, Shizuko Hiryu + Show 4 more

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https://doi.org/10.1038/s41598-020-67470-z

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Abstract

Using echolocation, bats receive acoustic information on their surroundings, which is assumed to help them sophisticatedly navigate complex environments. In this study, to understand spatial learning and acoustic sensing in bats, we investigated how flight and echolocation control changed in Rhinolophus ferrumequinum nippon as they learnt about their surroundings in an obstacle course that they flew through repeatedly. In these experiments, two testing environments (acoustically permeable and acoustically reflective) were prepared using chains and acrylic boards as obstacles to evaluate the interactive effects of spatial learning and flight environments. We found that bats reduced the meandering width of their flights and pulse emissions, and also seemed to reduce their shifts in pulse direction as they learnt more about their environments in both conditions. Throughout all our experiments, the bats with slower flight speeds tended to emit more pulses, which suggests that the number of pulse emissions reflects the echolocation tactics of each bat. The maximum flight speed was especially increased in the acoustically permeable condition, with frequent emissions of multiple pulses (≧triplets) in the early stages of flight, suggesting that bats adjust their flight plan based on how much of their surroundings they are able to sense in advance.

Highlights

Using echolocation, bats receive acoustic information on their surroundings, which is assumed to help them sophisticatedly navigate complex environments
Given that acoustic gaze is a parameter that may be used to investigate the spatio-temporal attention of an a nimal[9,21], we aim to examine how bats change the control of their spatio-temporal echolocation by focusing on the emission of multiple pulses, pulse directions, and flight paths
The obstacle layout was arranged to be a course which forced bats to fly with an S-shape flight path (Fig. 1b)

Summary

Introduction

Bats receive acoustic information on their surroundings, which is assumed to help them sophisticatedly navigate complex environments. Echolocating bats may shift their acoustic gaze i.e. the direction of their ultrasound pulses in terms of their flight path, given that their acoustic field of view with one transmitter and two receivers is spatially limited[8].For example, Japanese house bats (Pipistrellus abramus) emit pulses, towards their immediate target, and towards their intended target while chasing multiple prey[9] This indicates that bats plan their future flight paths by controlling the beam direction of their pulses in advance in environments with unpredictable s urroundings[10]. Previous studies for Eptesicus fuscus reported that these strobe groups increase when bats target an insect that moves unpredictably[12] and when bats fly in narrow spaces surrounded by multiple o bstacles[17,18,19] These studies concluded that the temporal pattern of pulse emission timings is affected by the difficulty in predicting the spatial properties of flight e nvironments[12,19]. Eptesicus fuscus were shown to reduce their pulse repetition rate and rapidly stabilise their flight path to Scientific Reports | (2020) 10:10751 |

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