Activity Patterns of Cave-Dwelling Bat Species during Pre-Hibernation Swarming and Post-Hibernation Emergence in the Central Appalachians

Abstract

In North America, bat research efforts largely have focused on summer maternity colonies and winter hibernacula, leaving the immediate pre- and post-hibernation ecology for many species unstudied. Understanding these patterns and processes is critical for addressing potential additive impacts to White-nose Syndrome (WNS)-affected bats, as autumn is a time of vital weight gain and fat resources are largely depleted in early spring in surviving individuals. Our study sought to examine autumn and spring bat activity patterns in the central Appalachian Mountains around three hibernacula to better understand spatio-temporal patterns during staging for hibernation and post-hibernation migration in the post-WNS environment. From early September through November 2015 and 2016, and from early March through April 2016 and 2017, we assessed the effects of distance to hibernacula and ambient conditions on nightly bat activity for Myotis spp. and big brown bats (Eptesicus fuscus) using zero-crossing frequency division bat detectors near cave entrances and 1 km, 2 km, and 3 km distant from caves. Following identification of echolocation calls, we used generalized linear mixed effects models to examine patterns of activity across the landscape over time and relative to weather. Overall bat activity was low at all sample sites during autumn and spring periods except at sites closest to hibernacula. Best-supported models describing bat activity varied, but date and ambient temperatures generally appeared to be major drivers of activity in both seasons. Total activity for all species had largely ceased by mid-November. Spring bat activity was variable across the sampling season, however, some activity was observed as early as mid-March, almost a month earlier than the historically accepted emergence time regionally. Current timing of restrictions on forest management activities that potentially remove day-roosts near hibernacula when bats are active on the landscape may be mismatched with actual spring post-hibernation emergence. Adjustments to the timing of these restrictions during the spring may help to avoid potentially additive negative impacts on WNS-impacted bat species.

Female little brown bats require both building and natural roosts in a mountainous environment with short summers

“…These results are consistent with unfavorable conditions delaying juvenile development due to maternal use of torpor (e.g., Burles et al, 2009;Racey & Swift, 1981). Despite reproductive delays, we did not acoustically detect little brown bats later than early October, consistent with hibernation in Alberta beginning in mid-to late September (Schowalter et al, 1979), approximately one month earlier than in more southern locations (e.g., Humphrey & Cope, 1976;Muthersbaugh et al, 2019). The challenges of successfully reproducing in a short season are apparent in our estimated reproductive rate of 30%, which is among the lowest values in the literature (e.g., Barclay et al, 2004;Frick et al, 2010;Loeb et al, 2014) and is in stark contrast to southern locations where rates consistently approach 100% (e.g., Humphrey & Cope, 1976;O'Farrell & Studier, 1975).…”

White‐nose Syndrome and Environmental Correlates to Landscape‐Scale Bat Presence

“…However, other acoustic studies have documented a similar lack of relationship between basal area and bat detection (Hein et al 2009), and other fine-scale vegetation measurements may be more appropriate (Ford et al 2005). Precipitation often can have a negative impact on nightly bat activity and detection (Erickson and West 2002, Yates and Muzika 2006, Muthersbaugh et al 2019b), yet we generally found no effect. Bats are known to forage in light rain (Erkert 1982) and only delayed emergence minimally when rain noises were played outside roosts (Geipel et al 2019).…”

Seasonal roost selection and activity of a remnant population of northern myotis in Pennsylvania

“…During the swarm, bats are thought to evaluate potential hibernacula while spending the day in roosts such as trees, buildings, and rock crevices outside of hibernacula [19,20]. Although swarming is well-known to include a noticeable increase in activity at hibernacula [21], little is known about the roosts used by bats during this time. This knowledge gap may hinder management of seasonally important habitats, a matter of increasing importance as species receive protected conservation status.…”