Comparing Bat Detector Deployments at Different Heights, In

Comparing Bat Detector Deployments at Different Heights, In
Comparing bat detector deployments at different heights, in different
orientations, and using different microphone types
1
Chenger
2
Tyburec
J.D.
and J.D.
1Bat Conservation and Management, Inc.; 2Janet Tyburec Consulting/Tucson
Do time-tested protocols for deploying bat detectors in the field
apply equally to the new array of full-spectrum detectors and
microphone types now available for acoustic inventories?
Protocols for bat detector deployments have been based largely on
results from frequency-division, AnaBat™ detectors1,2. These
protocols have been repeated faithfully, not only for other AnaBat
studies3, but also endorsed for inventories using full-spectrum
detectors4,5,6.
In this study, we question the blanket application of bat detector
protocols to modern full-spectrum detectors, especially since both
laboratory and field experiments have recently shown uneven
frequency responses and probabilities of detection amongst many
of these different detectors7.
Materials and Methods
5 States
7 Counties
8 Locations
11 unique deployments
12 different bat detector models and/or microphones tested
Results
Conclusions
Eight of 9 trials comparing directional D500x microphones and
omni-directional Wildlife Acoustics SMX-US microphones returned
results with the omni-directional microphones routinely detecting
up to three times more echolocation calls. However, the omnidirectional microphones collected between 10 and 35% fewer
recordings that could be confidently identified to species.
Focus
Discussion
Height
Place mic at least 5-meters agl to collect
high-quality recordings that can be
confidently identified to species.
If deploying at < 2-meters, use a 45° angle
Orientation
up orientation to increase detections.
Weather-proofing applied to full-spectrum D500x microphones, e.g.,
a snorkel or tube protecting the microphone element from rain,
returned the fewest number of recordings, and smallest percentage
of recordings that could be identified to species by our autoclassifier when compared to similar microphones in unprotected
deployments at the same site.
Don’t use
Weatherproof
“Tubes”
Weatherproofing reduces performance of
any ultrasonic mic8, and high sample rates
of full spectrum show more distortion. A
modern mic is weather resistant if aimed
so moisture doesn’t sit on the element, so
little or no added shielding is needed.
Mic. Type
Use a high-quality mic with an even
frequency response from the lowest to the
highest expected frequencies (15-110
kHz); as it will return more recordings that
can be confidently identified to species.
Mic.
Direction
An omni-directional mic will collect more
recordings; a directional mic will collect
more recordings that can be more
confidently identified to species.
Two trials, one in PA and one in KY, testing microphone height
above ground using a high-quality Pettersson D500x external mic,
oriented at 45-degrees above horizontal, resulted in between 8-19%
more bat passes that were confidently identified to species with the
“High” mic than with the “Low” mic.
Table 1.
Total identifiable bat passes recorded by mics at different heights
D500x Mic. @ 45°
PA Location
KY Location
Low (1.5 meters)
1,115
817
39 nights of trials with successful consecutive monitoring
40 gigabytes of data analyzed using SonoBat 3.2.0 classifiers
380 hours of paired recordings
High (6 meters)
1,203
973
Figure 2.
Nine paired deployments with a directional (D500x) vs. omnidirectional (Wildlife Acoustics SMX-US) mic show relative difference
in % of recordings ID’d to species by the SonoBat auto-classifier.
100.0#
90.0#
80.0#
70.0#
60.0#
50.0#
40.0#
30.0#
20.0#
10.0#
0.0#
AZ1#
AZ2#
AZ3#
AZ4#
High v. Low
Priceless amount of information learned!
+ 88 (8%)
KY1#
KY2#
PA#
UT#
OmniAdirec:onal#
+ 156 (19%)
Literature Cited
5Morris,
CA#
survey locations
Direc:onal#
16,000 files collected
R.E., W.L. Gannon, and S. Haymond. 2000. The efficacy of
acoustic techniques to infer differential use of habitat by bats. Acta
Chiropterologica, 2(2): 145-153.
2Weller, T.J. and C.J. Zabel. 2002. Variation in bat detections due to
detector orientation in a forest. Wildlife Society Bulletin, 30(3):
922-930.
3Rodhouse, T.J., K.T. Vierling, and K.M. Irvine. 2011. A practical
sampling design for acoustic surveys of bats. Journal of Wildlife
Management, 75(5): 1094-1102.
4Biscardi, S., J. Orprecio, M.B. Fenton, A. Tsoar, and J.M. Ratcliffe.
2004. Data, sample sizes, and statistics affect the recognition of
species of bats by their echolocation calls. Acta Chiropterologica, 6(2):
347-363.
Our findings suggest that full-spectrum microphone and detector
configurations require the following considerations to perform the
most effective acoustic surveys:
In all 5 trials where the Wildlife Acoustics SMX-UT and/or EM3
microphones were tested, they performed worse than the SMX-US
microphone for recording high-quality bat passes that could be
identified to species. Moreover, they detected fewer species than the
SMX-US and all other microphones tested.
17 months
1Sherwin,
Figure 1.
Eight detector microphones deployed during a 1-night trial in CA.
% of recordings ID’d to species
Introduction
A.D., D.A. Miller, M.C. Kalcounis-Rueppell. 2010. Use of
forest edges by bats in a managed pine forest landscape. Journal of
Wildlife Management, 74(1): 26-34.
6U.S. Fish and Wildlife Service, 2014 Range-wide Indiana Bat
Summer Survey Guidelines. Accessed 15 January 2014
(http://www.fws.gov/midwest/endangered/mammals/inba/
inbasummersurveyguidance.html)
7Adams, A.M., M.K. Jantzen, R.M. Hamilton, and M.B. Fenton. 2012.
Do you hear what I hear? Implications of detector selection for
acoustic monitoring of bats. Methods in Ecology and Evolution, 3:
992-998.
8Corben C. and K. Livengood. 2014. Weather Protection for AnaBat
Detectors. Northeast Bat Working Group Poster Presentation, 10
January 2014, Clinton NJ.
During these trials, we shared our preliminary results with detector
manufacturers, and they have been intrigued by our findings. Now
in addition to the Binary Acoustic Technology miniMIC and the
Pettersson M500, there will be new Wildlife Acoustics microphones
and detectors to test beginning in early 2014, which may address
some of the performance concerns raised by our 2012-2013 trials.
Acknowledgements
Further Information
Special thanks to: AnaBat™, Chris Corben; Arizona Game and Fish
Department, Tim Snow; Binary Acoustics Technology, LLC, Mark
Jensen; Kentucky Department of Fish and Wildlife Resources, Brooke
Hines; Mammoth Cave National Park, Rick Toomey and Steve
Thomas; Normandeau Environmental Consultants, Crissy Sutter; Park
Mammoth Resort, Nick Noble; Pettersson Elektronik AB, Lars
Pettersson; SonoBat™, Joe Szewczak; and Wildlife Acoustics, Ian
Agranat and Sherwood Snyder - for providing detectors, microphones,
software and/or deployment assistance, advice, and troubleshooting
services to assist with this project.
A 53-image, PDF document describing each deployment in this
trial, along with an extensive narrative explaining the results and
conclusions, is available for viewing or download at:
http://batmanagement.com/Ordering/acoustic/reviews/
2013MicComparisons.pdf
Complete results from bat detector microphone comparisons,
including spectrographs of paired recordings, can be viewed at:
http://www.batmanagement.com/Ordering/acoustic/reviews/
bdcompared1.html
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