Adaptive control over sonar field of view by the big brown bat, Eptesicus fuscus, during prey capture
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1
University of Maryland, College Park, Institute for Systems Research, United States
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2
University of Maryland, College Park, United States
Echolocating bats face the task of navigating a complex world through acoustic signals. They use information extracted from returning sonar echoes to adjust subsequent sonar call parameters for the purposes of navigation and prey capture. Previous research has examined how the bat modifies the features of its sonar calls (i.e. amplitude, duration, rate, and direction), but coordinated changes in the direction of the sonar beam and body positioning have not yet been measured in bats tracking objects in space. The purpose of this project is to understand how the bat orients its head, ears, and sonar beam during prey capture. We trained echolocating big brown bats to rest on a platform and track a tethered insect approaching at different speeds. The spatial extent of the bat’s sonar beam was recorded using a 30 channel wideband ultrasonic microphone array (20-100 kHz) while concurrent measurements of the head and ear positions were recorded with a high speed motion capture system (Vicon). Preliminary analysis of the sonar beam shape reveals an increase in the width of the bat’s sonar beam when the insect makes an unexpected change in velocity. Increasing the width of the sonar beam opens the angle of the bat’s acoustic view. We also found motion of the bat’s ears that was adapted to target distance and velocity. In general, the bat increases the distance between its ears as the target approaches, presumably to capture a larger extent of its acoustic scene. Furthermore, if the insect makes an unexpected change in velocity, the distance between the bat’s ears also increases. We hypothesize that the bat adjusts its ear position in response to uncertainty of the insect’s trajectory, and increasing the distance between its ears ensures that returning echoes fall within its acoustic view. The changes in ear position complement the changes observed in sonar beam width, suggesting that the bat increases its field of view of the acoustic scene when target motion is less predictable. The results of this study shed light on the complex coordination of vocalizations and body orientation during prey capture in an echolocating bat, and motivate further experiments analyzing behavioral changes for more complicated prey trajectories and the influences of cluttered acoustic scenes.
Acknowledgements
The authors wish to thank Dr. Ed Smith for help in designing the microphone array , Joe Kasnadi and Delphia Varadarajan for help in building the array hardware. Thanks to Prof. Timothy Horiuchi for helpful suggestions and mentoring.
Keywords:
bat sonar,
Beam pattern,
Echolocation,
sensorimotor integration
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster Presentation (see alternatives below as well)
Topic:
Sensorimotor Integration
Citation:
Krishnan
L,
Wohlgemuth
M,
Cox
O and
Moss
C
(2012). Adaptive control over sonar field of view by the big brown bat, Eptesicus fuscus, during prey capture.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00013
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Received:
01 May 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Ms. Lakshmi Krishnan, University of Maryland, College Park, Institute for Systems Research, College Park, MD, United States, lakshmik@umd.edu