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Interpulse interval modulation by echolocating big brown bats (Eptesicus fuscus) in different densities of obstacle clutter

Abstract

Big brown bats (Eptesicus fuscus) use biosonar to find insect prey in open areas, but they also find prey near vegetation and even fly through vegetation when in transit from roosts to feeding sites. To evaluate their reactions to dense, distributed clutter, bats were tested in an obstacle array consisting of rows of vertically hanging chains. Chains were removed from the array to create a curved corridor of three clutter densities (high, medium, low). Bats flew along this path to receive a food reward after landing on the far wall. Interpulse intervals (IPIs) varied across clutter densities to reflect different compromises between using short IPIs for gathering echoes rapidly enough to maneuver past the nearest chains and using longer IPIs so that all echoes from one sound can be received before the next sound is emitted. In high-clutter density, IPIs were uniformly shorter (20–65 ms) than in medium and low densities (40–100 ms) and arranged in “strobe groups,” with some overlap of echo streams from different broadcasts, causing pulse-echo ambiguity. As previously proposed, alternating short and long IPIs in strobe groups may allow bats to focus on large-scale pathfinding tasks as well as close-in obstacle avoidance.

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Acknowledgments

We thank H. Baqaen for assistance with Matlab programming, R. Bragg for assistance with bat training, E. Mullen for assistance with chain matrix construction, and M. Bates and M. Gonchar for assistance in data analysis. Work was supported by NIMH grant #R01MH069633 and ONR grant #N00014-0-1-0415 to J. A. Simmons. The experiment complied with the “Principles of Animal Care”, publication No. 86-23, revised 1985 of the National Institute of Health, and was approved by the Brown University IACUC.

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Correspondence to Anthony E. Petrites.

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Petrites, A.E., Eng, O.S., Mowlds, D.S. et al. Interpulse interval modulation by echolocating big brown bats (Eptesicus fuscus) in different densities of obstacle clutter. J Comp Physiol A 195, 603–617 (2009). https://doi.org/10.1007/s00359-009-0435-6

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Keywords

  • Bioacoustics
  • Echolocation
  • Interpulse interval
  • Clutter
  • Eptesicus fuscus