Ecology and Vulnerability

Hoary Bat

Little information was found about the biological responses of the Northeast’s bat RSGCN to climate change. However, bats in the northeastern U.S. will likely be especially sensitive to climate change because much of their biology, including reproduction and hibernation, is closely related to temperature (Loeb and Winters, 2013). For instance, increasing winter temperatures will likely cause warmer microsites where bats hibernate (Boyles et al., 2017), and variation in ambient microsite temperature increases energy expenditure by hibernating bats (Boyles and McKechnie, 2010). Hibernacula near cave entrances are quickly affected by outside temperatures, as opposed to sites deeper in more shielded caves (Boyles et al., 2017). However, even small temperature variations can significantly increase energy expenditure across winter (Boyles and McKechnie, 2010), so areas with a large range of microclimates may hold on to their bat populations while those with a more limited range may not (Boyles et al., 2017). Despite that, some evidence suggests that ambient temperature may not be the most important factor in energy conservation during hibernation, as behavior, humidity, and initial fat mass were also important factors for Tricolored Bats (McGuire et al., 2021) and Tricolored Bats experimentally held in varying temperatures during hibernation showed no difference in metabolic rate when hibernation ended (Boyles et al., 2022).

Shift in Range, Elevation, or Depth

Experimental evidence suggests that bat species that roost in warmer microhabitats, such as Hoary Bats in foliage, have a higher heat tolerance than those that roost in more protected areas, like Little Brown and Silver–haired Bats that roost in tree crevices (Noakes et al., 2021). Hoary Bats are known to only roost in Eastern Hemlock (Tsuga canadensis; Veilleux et al., 2009), which is experiencing drastic declines in the Northeast due to the Hemlock Wooly Adelgid (Adelges tsugae), which will expand farther in the Northeast due to climate change (Paradis et al., 2008; Ellison et al., 2018). This Wooly Adelgid expansion and subsequent die-off of Eastern Hemlock may effectively destroy much of the Hoary Bat’s roosting habitat.