Surveying for flying squirrels using traditional techniques produces extremely low detection rates compared to ultrasonic acoustics. Within Pennsylvania, northern flying squirrels Glaucomys sabrinus macrotis (NFS) are state listed as endangered due to habitat loss and parasite-mediated competition by and hybridization with southern flying squirrels Glaucomys volans (SFS). This subspecies is isolated from adjacent populations in West Virginia and New York, and has experienced drastic population declines. The discovery and characterization of ultrasonic vocalizations of NFS and SFS, as well as successful field surveys using ultrasonic acoustic detectors in the southern Appalachian Mountains, highlights the potential use of this technique for determining presence of NFS. To confirm the feasibility of using this technique on declining populations of NFS sympatric with SFS, we conducted 108 nights of passive ultrasonic acoustic surveys for NFS at six survey areas using two detectors per survey area (N=12 detectors) in June 2017. We considered sites high quality ‘High’ or low quality ‘Low’ based on number of physical capture records during the last two decades and the dominance of boreo-montane conifer tree species in the overstory. We detected NFS at four study areas and SFS at all six study areas. We found higher average probability of detection (POD) for NFS in High vs. Low sites (0.28±0.06 SE and 0.09±0.7, respectively), whereas POD was similar for SFS between High vs. Low sites (0.13±0.05 and 0.17±0.05, respectively). We also found NFS had lower latency of detection (LTD) at High and Low sites (2.7±0.8 nights and 7.83±1.5, respectively), whereas LTD for SFS did vary not between sites (5±1.6 nights and 3.8±1.5, respectively). Our study shows acoustics can be successfully used to efficiently survey NFS in Pennsylvania, where populations are small and monitoring these populations more effectively is critical to determining changes in persistence due to climate- and disease-induced factors.

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