Seven-year impact of white-nose syndrome on tri-colored bat (Perimyotis subflavus) populations in Georgia, USA

Abstract

White-nose syndrome (WNS) has emerged as the most serious threat to North American cave-dwelling bat species, with an estimated mortality of over 6 million since it was first documented in the USA in 2006. Tri-colored bat Perimyotis subflavus is one of the species most affected, with hibernaculum counts at caves in WNS-positive regions reduced by >90% from previous counts. While declines have been documented in hibernaculum surveys, long-term monitoring programs during active seasons provide a unique opportunity to examine population trends and impact of population declines post-WNS. We developed generalized linear mixed models using data from a state-wide, long-term (2011-2020) mobile bat acoustic monitoring program in Georgia, USA, to better understand P. subflavus population trends before and after disease detection and between WNS-negative and WNS-positive regions. We recorded 5046 P. subflavus passes across all acoustic routes during the 10 yr time period. We detected a significant decrease in activity 2 yr after disease detection in the WNS-positive region, whereas activity in the WNS-negative region remained stable over time. Understanding changes in bat populations as WNS spreads and measuring the magnitude of population declines to assess disease impacts is crucial for providing appropriate guidance for management. Our results provide evidence of the critical status of P. subflavus in the southernmost WNS-positive region, but also emphasize the importance of monitoring WNS spread to new regions, as those that remain WNS-free could provide refugia for the species and a potential source of recolonization to WNS-affected areas.

A decade of hibernating bat communities along the periphery of a region of white‐nose syndrome

“…Population declines in tricolored bat hibernaculum counts in our study are consistent with patterns in other WNS-positive regions of the eastern United States (Langwig et al 2012, Powers et al 2015, Frick et al 2017, Loeb and Winters 2022. Trends are similar to those found during hibernation (Loeb and Winters 2022) and activity patterns during summer obtained from acoustic monitoring (Perea et al 2022) along the periphery of the white-nose syndrome endemic region. Our results indicated a decline of approximately 90% in the first 3 years after WNS detection, followed by stabilization, as has been documented in hibernating populations of tricolored bats in other regions (Frick et al 2017, Loeb andWinters 2022).…”

“…Differences in population decline following the introduction of Pd have been documented over time periods ranging from 1 to 5 years, varying by species and region (Bernard and McCracken 2017, Frick et al 2017, Barr et al 2021). In a long‐term acoustic monitoring study in Georgia, Perea et al (2022) observed declines in relative activity of tricolored bats 2 years after WNS detection, with activity reaching a stable minimum 3 years after the disease was first documented in northern Georgia (USFWS 2019).…”

“…Our study documents temporal trends in overwintering bat populations along the periphery of the white-nose syndrome endemic region. As WNS continues to spread and invade new regions of North America, examining population trends will be important for designing strategies to address similar scenarios in the future(Bernard et al 2019(Bernard et al , 2020Perea et al 2022). While the stable population of gray bats at the most southeastern limit of its range may indicate that its current habitat and conservation efforts are effective, the decline of northern long-eared bats suggests that urgent action is needed to prevent its extinction.…”

Literature review of tri-colored bat natural history with implications to management

“…Bats in hibernacula infected with WNS have more activity than noninfected hibernacula, including flights over the landscape in cooler temperatures (Bernard and McCracken, 2017). In addition to observed fatalities at hibernacula, WNS has also been linked to decreased regional populations (Turner et al, 2011;Ingersoll et al, 2013;Ingersoll et al, 2016;Perry and Jordan, 2022), cave-bat abundance in summer habitats (Dzal et al, 2010;Brooks, 2011;O'Keefe et al, 2019, Deeley et al, 2021Johnson et al, 2021;Loeb and Winters, 2022;Perea et al, 2022) as well as winter hibernacula (Lacki et al, 2015;Powers et al, 2015;Perry and Jordan, 2020).…”