Ecology and Vulnerability

Indiana Bat

There was not much information about the biological responses to climate change of the Northeast’s bat RSGCN identified in the literature search. 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 caves, which are more shielded (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). 

Variations in precipitation patterns that lead to increased drought and more extreme storms will likely affect foraging conditions for bats. Insect populations often decline during drought (Hawkins and Holyoak 1998), resulting in increased foraging costs and decreased annual survival for bats (Loeb and Winters 2013). Most insectivorous bats must drink to maintain water balance, and water needs increase considerably during pregnancy and lactation (Kurta et al., 1989, 1990; Adams and Hayes 2008). As such, severe droughts, especially when combined with unusually cold or hot temperatures, will likely lead to lower reproductive success rates (Bourne and Hamilton-Smith 2007; Adams 2010). 

Changes in precipitation patterns are already contributing to more severe wildfires across North America, specifically in boreal forests (Stephens et al., 2014). The increased risk that wildfires may impose on bat populations is not well known (Jung 2020); though, studies evaluating the effect of smaller, prescribed burns have shown burned areas benefit bats in creating better roosting and foraging opportunities (e.g., Ford et al., 2016, O’Keefe and Loeb 2017). While smaller prescribed burns may increase bat activity in some areas, larger wildfires can have negative impacts on some species (e.g., Snider et al., 2013, but see Buchalski et al., 2013). For example, after a “megafire” in the boreal forest of Yukon, Canada, despite creating more open areas for Little Brown Bats to forage, bat activity in the burned areas was much lower than in nearby unburned areas, with almost no activity occurring in burned upland areas (Jung 2020). Importantly, sites of “megafires” in eastern Canada in the summer of 2023 may provide a good opportunity to work with Canadian colleagues to explore post-fire habitat usage.

There is still much to learn about how these ecologically important species that provide valuable ecosystem services as consumers of nuisance insects (CITE) are and will be impacted by climate change. Much of the research on these bat species has focused on roosting and hibernating site selection and how these sites may influence energy budgets. However, since bats are highly mobile, one particularly large data gap exists in considering how these species will shift their geographic ranges, especially for one species with a projected range shift (Indiana Bats) indicating it could abandon most of its summer range in the midwestern U.S. for the northeastern U.S. in the next 50 years (Loeb and Winters 2013). Having reasonable estimates of where these species may be in the near- and long-term is crucial in developing management plans for the future. While none of the northeastern bats of greatest conservation need had much research on biological responses to climate change, we found no research at all for one-third of these species. Other major data gaps include a complete lack of published data on how climate change will affect population trends or changes in the physiology and morphology of RSGCN bats in the Northeast and how any indirect effects of climate change will impact them.

Shifts in Range, Elevation, or Depth

As mentioned above, Indiana Bats may shift their summer maternity distribution from the midwestern U.S. to the northeastern U.S. and Appalachian Mountains, with the western part of their maternity range (Missouri to Ohio) likely becoming unsuitable due to increasing temperatures during the maternity season under most future climate projections (Loeb and Winters 2013). To reduce some of the effects of a warming climate, Indiana Bats may use local site selection (e.g., select trees under dense canopy) to mediate the effects of warming temperatures before abandoning an area (Loeb and Winters 2013). For instance, female Indiana Bats in Missouri selected roosts deeper in the shade on days with higher temperatures in the morning and roosts more exposed to the sun on days with lower temperatures (Callahan et al., 1997), which is a similar shift in the American Pika’s (Ochotona princeps) thermal habitat use and behavioral adaptive capacity (Beever et al., 2016). Managing Indiana Bat habitat in the northeastern United States and the Appalachian Mountains of the Southeast is important since these areas will likely serve as climate refugia for this species (Loeb and Winters 2013; for more on climate refugia, see Morelli et al., 2016).

Shifts in Phenology

Indiana Bats have not appeared to change their arrival and departure dates to and from their summer colonies in Indiana between 1998 --– 2014 very much (Petitt and O’Keefe 2017), which suggests that photoperiod and/or developmental physiology may be the most important cues driving migration phenology, but more research is needed (Petitt and O’Keefe 2017).