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Effects of Environmental Clutter on Synthesized Chiropteran Echolocation Signals in an Anechoic Chamber

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Department of Fish and Wildlife Conservation, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
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Engineering Mechanics Program, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
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Department of Mathematics, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
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Virginia Cooperative Fish and Wildlife Research Unit, U.S. Geological Survey, Blacksburg, VA 24061, USA
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West Virginia Division of Natural Resources, Elkins, WV 26241, USA
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Roanoke City Public Schools, Roanoke, VA 24012, USA
*
Author to whom correspondence should be addressed.
Academic Editor: C. W. Lim
Acoustics 2021, 3(2), 391-410; https://doi.org/10.3390/acoustics3020026
Received: 26 February 2021 / Revised: 6 June 2021 / Accepted: 7 June 2021 / Published: 11 June 2021
Ultrasonic bat detectors are useful for research and monitoring purposes to assess occupancy and relative activity of bat communities. Environmental “clutter” such as tree boles and foliage can affect the recording quality and identification of bat echolocation calls collected using ultrasonic detectors. It can also affect the transmission of calls and recognition by bats when using acoustic lure devices to attract bats to mist-nets. Bat detectors are often placed in forests, yet automatic identification programs are trained on call libraries using echolocation passes recorded largely from open spaces. Research indicates that using clutter-recorded calls can increase classification accuracy for some bat species and decrease accuracy for others, but a detailed understanding of how clutter impacts the recording and identification of echolocation calls remains elusive. To clarify this, we experimentally investigated how two measures of clutter (i.e., total basal area and number of stems of simulated woody growth, as well as recording angle) affected the recording and classification of a synthesized echolocation signal under controlled conditions in an anechoic chamber. Recording angle (i.e., receiver position relative to emitter) significantly influenced the probability of correct classification and differed significantly for many of the call parameters measured. The probability of recording echo pulses was also a function of clutter but only for the detector angle at 0° from the emitter that could receive deflected pulses. Overall, the two clutter metrics were overshadowed by proximity and angle of the receiver to the sound source but some deviations from the synthesized call in terms of maximum, minimum, and mean frequency parameters were observed. Results from our work may aid efforts to better understand underlying environmental conditions that produce false-positive and -negative identifications for bat species of interest and how this could be used to adjust survey accuracy estimates. Our results also help pave the way for future research into the development of acoustic lure technology by exploring the effects of environmental clutter on ultrasound transmission. View Full-Text
Keywords: acoustics; anechoic chamber; angle; bats; environmental clutter; lure; ultrasonic acoustics; anechoic chamber; angle; bats; environmental clutter; lure; ultrasonic
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MDPI and ACS Style

Freeze, S.R.; Shirazi, M.; Abaid, N.; Ford, M.; Silvis, A.; Hakkenberg, D. Effects of Environmental Clutter on Synthesized Chiropteran Echolocation Signals in an Anechoic Chamber. Acoustics 2021, 3, 391-410. https://doi.org/10.3390/acoustics3020026

AMA Style

Freeze SR, Shirazi M, Abaid N, Ford M, Silvis A, Hakkenberg D. Effects of Environmental Clutter on Synthesized Chiropteran Echolocation Signals in an Anechoic Chamber. Acoustics. 2021; 3(2):391-410. https://doi.org/10.3390/acoustics3020026

Chicago/Turabian Style

Freeze, Samuel R., Masoud Shirazi, Nicole Abaid, Mark Ford, Alexander Silvis, and Dawn Hakkenberg. 2021. "Effects of Environmental Clutter on Synthesized Chiropteran Echolocation Signals in an Anechoic Chamber" Acoustics 3, no. 2: 391-410. https://doi.org/10.3390/acoustics3020026

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