Testing a new passive acoustic recording unit to monitor wolves

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Shannon M. Barber-Meyer, USGS, Ely, MN, Vicente Palacios, ARCA, People and Nature, S.L. and ACNHE, Association for the Conservation of Nature in Human Environments, Spain, Barbara Marti Domken, ACNHE, Association for the Conservation of Nature in Human Environments, Spain and Lori Schmidt, International Wolf Center, Ely, MN

Background/Question/Methods
As part of a broader trial of noninvasive methods to research wild wolves (Canis lupus) in Minnesota, USA, we explored whether wolves could be remotely monitored using a new, inexpensive, remotely-deployable, noninvasive, passive acoustic recording device, the AudioMoth. We tested the efficacy of AudioMoths in detecting wolf howls and factors influencing detection by placing them at set distances from a captive wolf pack and compared those recordings with real-time, on-site howling data between May 22 – June 17, 2019.
Results/Conclusions
We identified 1531 vocalizations that we grouped into 428 vocal events (236 solo howl series and 192 chorus howls). The on-site AudioMoth correctly recorded 100% of chorus and solo howls that were also documented in real-time. The remote array detected 49.5% of chorus and 11.9% of solo howls (at least one unit detected the event). The closest remote AudioMoth (0.54 km, 1/3 mi) detected 37% of choruses and 8.9% of solo howls. Chorus howls (9.4%) were detected at even the farthest unit (3.2 km, 2 mi). Favorable wind (carrying source howls to the remote units) and calm (no wind) conditions increased detectability and detection distance of chorus howls. Temperature was inversely related to detection. Given the detection distances we observed, AudioMoths are probably most useful in studying specific sites during periods when wolves move less frequently (e.g., during late spring and summer at homesites or potentially during winter at kill sites of very large prey). AudioMoths would also be useful in a passive sampling array (e.g., occupancy studies), especially when in concert with other methods such as camera trapping (Garland et al. 2020). Additional research should be conducted in areas with different environmental variables (e.g., wind, temperature, habitat, topography) to determine performance under varying conditions and also when fitted with a parabolic dish.