Ultrasonic Acoustic Surveys of State Endangered Northern Flying Squirrels in the Pocono Mountains, Pennsylvania

Surveying for flying squirrels by using traditional techniques produces extremely low detection rates compared with ultrasonic acoustics. Within Pennsylvania, the northern flying squirrel subspecies Glaucomys sabrinus macrotis is state listed as endangered due to habitat loss and parasite-mediated competition by and hybridization with the southern flying squirrel Glaucomys volans. 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 G. s. macrotis and G. volans, as well as successful field surveys with ultrasonic acoustic detectors in the southern Appalachian Mountains, highlight the potential use of this technique for determining the presence of G. s. macrotis. To confirm the feasibility of using this technique on declining populations of G. s. macrotis sympatric with G. volans, we conducted 108 nights of passive ultrasonic acoustic surveys for G. s. macrotis at six survey sites by using two detectors per survey site (N = 12 detectors) in June 2017. We considered sites high quality (“high”) or low quality (“low”) based on the number of physical capture records during the past 2 decades and the dominance of boreo-montane conifer tree species in the overstory. We detected G. s. macrotis at four study sites and G. volans at all six study sites. We found higher average probability of detection for G. s. macrotis in high vs. low sites (0.28 ± 0.06 [mean ± SE] and 0.09 ± 0.07, respectively), whereas probability of detection was similar for G. volans between high and low sites (0.13 ± 0.05 and 0.17 ± 0.05, respectively). We also found G. s. macrotis had lower latency of detection at high vs. low sites (2.7 ± 0.8 and 7.83 ± 1.5 nights, respectively) but G. volans did not vary in latency of detection between sites (5 ± 1.6 and 3.8 ± 1.5 nights, respectively). Our study shows acoustics can be successfully used to efficiently survey G. s. macrotis 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.