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Spatial unmasking in the echolocating Big Brown Bat, Eptesicus fuscus

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Abstract

Masking affects the ability of echolocating bats to detect a target in the presence of clutter targets. It can be reduced by spatially separating the targets. Spatial unmasking was measured in a two-alternative-forced-choice detection experiment with four Big Brown Bats detecting a wire at 1 m distance. Depth dependent spatial unmasking was investigated by the bats detecting a wire with a diameter of 1.2 mm in front of a masker with a threshold distance of 11 cm behind the wire. For angle dependent spatial unmasking the masker was turned laterally, starting from its threshold position at 11 cm. With increasing masker angles the bats could detect thinner wires with diameters decreasing from 1.2 mm (target strength −36.8 dB) at 0° to 0.2 mm (target strength −63.0 dB) at 22°. Without masker, the bats detected wire diameters of 0.16 mm (target strength −66.2 dB), reached with masker positions beyond 23° (complete masking release). Analysis of the sonar signals indicated strategies in the echolocation behavior. The bats enhanced the second harmonics of their signals. This may improve the spatial separation between wire and masker due to frequency-dependent directionality increase of sound emission and echo reception.

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Abbreviations

2AFC:

Two-alternative-forced-choice

SPL:

Sound pressure level

peSPL:

Peak equivalent sound pressure level

TS:

Target strength

RMS:

Root mean square

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Acknowledgments

We thank the whole ‘Bat Group’ of the Department of Animal Physiology for critical discussing the current topic. And we thank the Deutsche Forschungsgemeinschaft (SFB 550) for financial support.

Conflict of interest statement

The experiments reported here adhere to the “Principles of animal care” (publication no. 86–23, revised 1985 of the NIH) and also comply with the current German animal protection law. Bats were held in the animal facilities at the University of Tübingen (approved by the Regierungspräsidium Tübingen).

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  1. Lehrstuhl Tierphysiologie, Zoologisches Institut, Universität Tübingen, Auf der Morgenstelle 28, 72076, Tübingen, Germany

    Susan Sümer, Annette Denzinger & Hans-Ulrich Schnitzler

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  1. Susan Sümer
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  2. Annette Denzinger
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  3. Hans-Ulrich Schnitzler
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Correspondence to Hans-Ulrich Schnitzler.

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Sümer, S., Denzinger, A. & Schnitzler, HU. Spatial unmasking in the echolocating Big Brown Bat, Eptesicus fuscus . J Comp Physiol A 195, 463–472 (2009). https://doi.org/10.1007/s00359-009-0424-9

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