Coordinated Control of Acoustical Field of View and Flight in Three-Dimensional Space for Consecutive Capture by Echolocating Bats during Natural Foraging.

Miwa Sumiya,Masaru Kondo,Emyo Fujioka,Shizuko Hiryu,Kazuya Motoi,Michael Smotherman

doi:10.1371/journal.pone.0169995

Abstract

Echolocating bats prey upon small moving insects in the dark using sophisticated sonar techniques. The direction and directivity pattern of the ultrasound broadcast of these bats are important factors that affect their acoustical field of view, allowing us to investigate how the bats control their acoustic attention (pulse direction) for advanced flight maneuvers. The purpose of this study was to understand the behavioral strategies of acoustical sensing of wild Japanese house bats Pipistrellus abramus in three-dimensional (3D) space during consecutive capture flights. The results showed that when the bats successively captured multiple airborne insects in short time intervals (less than 1.5 s), they maintained not only the immediate prey but also the subsequent one simultaneously within the beam widths of the emitted pulses in both horizontal and vertical planes before capturing the immediate one. This suggests that echolocating bats maintain multiple prey within their acoustical field of view by a single sensing using a wide directional beam while approaching the immediate prey, instead of frequently shifting acoustic attention between multiple prey. We also numerically simulated the bats’ flight trajectories when approaching two prey successively to investigate the relationship between the acoustical field of view and the prey direction for effective consecutive captures. This simulation demonstrated that acoustically viewing both the immediate and the subsequent prey simultaneously increases the success rate of capturing both prey, which is considered to be one of the basic axes of efficient route planning for consecutive capture flight. The bat’s wide sonar beam can incidentally cover multiple prey while the bat forages in an area where the prey density is high. Our findings suggest that the bats then keep future targets within their acoustical field of view for effective foraging. In addition, in both the experimental results and the numerical simulations, the acoustic sensing and flights of the bats showed narrower vertical ranges than horizontal ranges. This suggests that the bats control their acoustic sensing according to different schemes in the horizontal and vertical planes according to their surroundings. These findings suggest that echolocating bats coordinate their control of the acoustical field of view and flight for consecutive captures in 3D space during natural foraging.

Highlights

Echolocating bats have remarkable ultrasonic sensing abilities
Our recent study adopted a mathematical methodology to estimate parameters representing the flight attention of bats for their measured flight paths during the phase of approaching prey [17]. This represents the attention by the bat toward a certain target prey in terms of flight.) We found that the distribution of the flight attention parameters corresponded to the optimal value of the parameter set in the numerical simulation, which showed a high success rate of consecutive prey captures
We found that, in the case of short-interval capture, the bats simultaneously maintained both their immediate and subsequent prey within the horizontal and vertical beam width of the emitted pulse

Summary

Introduction

Echolocating bats have remarkable ultrasonic sensing abilities. They emit directional ultrasonic signals and listen to the echoes returning from objects. It has been reported that echolocating bats actively change the pulse direction depending on the situation in a flight chamber [2,7,8,10,12] or even in the field [4,5] They have been reported to expand the beam width adaptively before capturing target prey to retain a moving target within the acoustical field of view [11,13] or to narrow the beam width when entering a confined space [14]. These studies demonstrated that bats actively adjust both the pulse direction and the beam width, as well as traditional acoustic characteristics, such as time-frequency structure, sound pressure level, or interpulse interval (IPI) [15,16]

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