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This is a post-peer-review, pre-copyedit version of a book chapter published in 
50 Years of Bat Research: Foundations and New Frontiers, edited by Lim et al. 
  
 
 
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DOI 10.1007/978-3-030-54727-1_13 
 
 
CITATION Johnson J.S., Blomberg A.S., Boyles J.G., Lilley T.M. (2021) 
The Winter Worries of Bats: Past and Present 
Perspectives on Winter Habitat and Management of 
Cave Hibernating Bats. In: Lim B.K. et al. (eds) 50 Years of 
Bat Research. Fascinating Life Sciences. Springer, Cham. 
https://doi.org/10.1007/978-3-030-54727-1_13 
 
 
 
 
 
 1 
The Winter Worries of Bats: Past and Present Perspectives on Winter Habitat and Management 
of Cave Hibernating Bats 
 
Joseph Johnson1*, Anna Blomberg2, Justin Boyles3, and Thomas Lilley4 
 
1 Department of Biological Sciences, Ohio University, Athens, Ohio, USA 
2 Department of Biology, University of Turku, Turku, Finland 
3 Cooperative Wildlife Research Laboratory, School of Biological Sciences, Southern Illinois 
University, Carbondale, Illinois, USA 
4 Finnish Museum of Natural History, University of Helsinki, Helsinki, Finland 
* Correspondent: jjohnson@ohio.edu 
 
Abstract 
 
Winter is a time of fascinating changes in biology for cave-hibernating bat species, but it is also a 
time of vulnerability. Unsurprisingly, assessments of winter habitat for these bats and how they 
can be managed has been a focus of many researchers involved with the North American Society 
for Bat Research over the last 50 years. During this time, a paradigm shift has occurred in the 
way these scientists think about factors driving winter habitat selection. To illustrate this shift, 
we review three hypotheses seeking to explain microclimate selection in cavernicolous bats. The 
first, which we call the “Colder is Better Hypothesis”, posits that bats should select cold 
microclimates that minimize energy expenditure. The second, the “Hibernation Optimization 
Hypothesis”, posits that bats should select microclimates that reduce the expression of torpor to 
balance energy conservation against non-energetic costs of hibernation. Finally, the “Thrifty 
Female Hypothesis” asserts that females should select colder microclimates than males to 
conserve energy for reproduction. We discuss these hypotheses, and the paradigm shift away 
from viewing hibernation as a phenomenon driven solely by the need to conserve energy, in the 
context of hibernacula management in North America. We focus on both historical and recent 
conservation threats, most notably alteration of thermal regimes and the disease white-nose 
syndrome. We urge against returning to an over-simplified view of winter habitat selection in 
response to our current conservation challenges.  
 
Key Words: conservation, ecophysiology, hibernation optimization, physiology, torpor, white-
nose syndrome 
 
1 The Winter Worries of Bats 
 
To the uninitiated, hibernation may appear as a relatively uneventful process, at times consisting 
of weeks of inactivity transpiring in a dark, unchanging environment. However, decades of 
research have taught us that hibernation is far more interesting. Although the life of a hibernating 
bat occurs at a much different pace than during summer, the winter lives of bats are dynamic, 
and the study of winter ecology is both rich in literature and riddled with gaps in knowledge. 
During winter, bats are not only under selective pressure to conserve energy, but face several 
competing physiological and ecological demands as well as opportunities (Thomas et al. 1979, 
1990; Humphries et al. 2003). Bats respond to these pressures in diverse ways, including 
periodic arousals, behavioral changes, and habitat selection (Boyles et al. 2007, 2008; Jonasson 
 2 
and Willis 2012). Unfortunately, while we have learned much about the winter lives of bats in 
the last 50 years, cavernicolous bats are currently more imperiled than ever, and proper 
conservation and management of these species will require detailed mechanistic understanding 
of habitat selection during hibernation. 
 The first study of hibernation presented at the North American Symposium on Bat 
Research, “Status, winter habitat, and management of the endangered Indiana bat, Myotis 
sodalis”, was delivered by Stephen Humphrey in 1975. While by no means the first study on the 
winter worries of bats (Hock 1951; Twente 1955; McNab 1974), this presentation, and a 
subsequent publication by the same author (Humphrey 1978), articulated concepts that remain 
relevant in bat conservation to this day. Presenting soon after passage of the Endangered Species 
Act, Humphrey linked disturbance and habitat degradation to the decline of Indiana myotis. 
Humphrey correlated events such as closing cave entrances, natural disasters, and disturbances 
from biologists, recreational cave visitors, and vandals to population declines and temperature 
changes inside hibernacula. Importantly, he also predicted that if winter disturbance from 
humans was eliminated, and microclimates were restored to 4–8 °C, Indiana myotis populations 
would recover and the species could be downgraded from endangered. At the time, a narrow 
range of cold temperatures was believed to be favorable due to the effect of temperature on 
metabolism (Hock 1951; Twente 1955; McManus 1974). Humphrey’s connection between 
energetics and the decline of an endangered species was a pivotal one, and for decades, the belief 
that suitable winter habitats were those with a narrow range of cold temperatures conducive to 
maximum energy savings was the dominant paradigm (Richter et al. 1993; Tuttle and Kennedy 
2002).  
  Recent studies have shifted our view of hibernation to emphasize that bats must balance 
more than energetics during winter (Thomas and Geiser 1997; Humphries et al. 2003; Boyles et 
al. 2007). These studies benefited from decades of prior research as well as technological 
advances allowing for more accurate measurements of both bats and their selected 
microclimates. There is now copious evidence against the caricature of hibernation as a period 
when bats require stable, cold temperatures (Boyles et al. 2007; Brack 2007; Kurta and Smith 
2014). Unfortunately, this knowledge has not always translated to more effective bat 
conservation because we still lack a fundamental, mechanistic understanding of many important 
aspects of winter ecology. Failure to recognize the full suite of factors driving winter habitat 
selection, for example, may result in management plans for hibernacula focused on a narrow 
range of temperatures that may at times be overly simplistic and focused on the wrong factors. 
This is supported by varied success of cave restoration exercises and examples of caves with 
“ideal” microclimates that are unused by hibernating bats (Elliott and Clawson 2007; Gore et al. 
2012). Our goal here is to review literature describing our evolving knowledge of winter habitat 
use and the implications of these studies for bat conservation and management. While our work 
is not meant to be exhaustive, it aims to put our current knowledge into a theoretical context. We 
summarize the factors known to contribute to microclimate selection, both within and among 
species, and across environments. We then review management approaches to date, and the need 
to adapt these perspectives to the current challenges of WNS. 
 
2 Factors Driving Microclimate Selection in Winter 
 
To illustrate how thought on winter habitat selection has evolved over the last several decades, 
we describe three hypotheses representing previous and contemporary views on the topic. The 
 3 
earliest hypothesis explaining microclimate selection by hibernating bats, which we call the 
Colder is Better Hypothesis, posits that bats select hibernacula with ambient temperatures (Ta) 
that minimize their torpid metabolic rate (TMR), thus minimizing energy spent during 
hibernation (Figure 1a). This hypothesis is built on the assumption that overwinter survival is 
negatively correlated with energy spent during hibernation, and that this selective pressure alone 
drives winter habitat use. Because TMR decreases with Ta down to a threshold below which 
hibernators must increase TMR to avoid freezing (Tmin), hibernating bats can maximize their 
energetic savings during winter by hibernating at Tas slightly above Tmin (Buck and Barnes 2000; 
Boyles and McKechnie 2010). Energy savings are maximized at Tas > Tmin because hibernacula 
microclimates vary during winter, and periodic drops in Ta below Tmin cause hibernators to incur 
greater energetic costs than hibernating at Tas consistently above Tmin. Hibernation at cold Tas 
also saves energy because these temperatures are associated with longer torpor bouts (McNab 
1974; Brack and Twente 1985; Dunbar and Tomasi 2006). Given that energetic cost of arousals 
constitutes the majority of a hibernating bat’s winter energy budget, increasing torpor bout 
duration can significantly reduce energy use (Thomas et al. 1990; Jonasson and Willis 2012).  
 Numerous studies during the 20th century reported observations of bats hibernating at 
cold Tas, seemingly in support of the Colder is Better Hypothesis (McManus 1974; Nagel and 
Nagel 1991; Tuttle and Kennedy 2002). However, such studies still often reported variation in 
Tas selected, and over time variation within and among species became apparent (Webb et al. 
1996). Also evident were numerous examples of cold hibernacula with absent or declining bat 
populations, and warmer sites where populations were not declining, apparently at odds with 
Colder is Better but without a framework for understanding why (Tuttle and Kennedy 2002; 
Elliott and Clawson 2007; Gore et al. 2012). An explanation began to emerge by the turn of the 
century with the realization that maintaining higher rates of metabolism during hibernation may 
be beneficial for non-energetic reasons (Humphries et al. 2003). This understanding, combined 
with recognition of the costs of torpor, led to the recognition that colder is not necessarily better. 
Costs of torpor are likely not fully understood, but include reduced immune function, disruptions 
of homeostatically controlled process such as sleep, exposure to predation and abiotic events, 
and loss of the physiological advantages of euthermy (Humphries et al. 2003; Heller and Ruby 
2004; Bouma et al. 2010). Thus, successful hibernators balance competing costs and benefits of 
torpor, and this revelation led to the articulation of new hypotheses predicting winter habitat 
selection (Boyles et al., In Review).  
 The Hibernation Optimization Hypothesis posits that bats should select microclimates 
where they can survive while reducing the use of torpor (Boyles et al. 2007). This hypothesis 
considers energetic constraints during hibernation, predicting that bats should select cold Tas 
when energy is scarce, but also predicts bats should avoid cold Tas when possible to minimize 
torpor costs (Figure 1b). Implicit to this hypothesis is the expectation that individuals vary in 
habitat selection based on their unique ecology and physiology. Boyles and colleagues (2007) 
were among the first to find support for this hypothesis, finding that little brown myotis (M. 
lucifugus) with greater energy reserves – fat – select warmer Tas because they can afford more 
frequent periodic arousals than bats with smaller energy reserves. This hypothesis could also be 
used to assess interspecific differences in habitat use. For example, although it is well known that 
different species often exhibit differences in microclimate preference, we currently lack suitable 
explanations for why some species prefer warmer or colder Tas (McNab 1974; Raesly and Gates 
1987; Brack 2007; Kurta and Smith 2014; Johnson et al. 2017). Comparisons of different species 
selecting where to hibernate from the same range of available microclimates may reveal 
 4 
important differences in ecology, such as energy needed for reproduction or migration, or 
physiology, such as metabolism or heat and water loss.  
 Within species, there are additional drivers of variation in torpor use and habitat selection 
beyond existing fat reserves. Jonasson and Willis (2011) developed the Thrifty Female 
Hypothesis based on their observations of different patterns of body mass loss between males 
and females during winter. The Thrifty Female Hypothesis posits that females should express 
torpor to a greater degree during winter because they face greater selective pressure to maximize 
energy savings than males (Figure 1c). Unlike males, female bats need additional fat reserves to 
ovulate upon emergence from hibernation and successfully fertilize with sperm stored over 
winter (Kunz et al. 1998). Thus, females have less energy available to mitigate the costs of torpor 
than males and are predicted to select colder microclimates within hibernacula than males with 
the same amount of fat. Since its articulation, this hypothesis has become a widely accepted 
aspect of Hibernation Optimization where each sex balances costs and benefits differently. 
However, data demonstrating that females use both relatively warm and cold regions within the 
same hibernacula (Boyles et al. 2007) despite pressure to maximize energy reserves, 
demonstrates that females still respond to the need to minimize costs of torpor to at least some 
degree. Bats may be unique among hibernators in their adherence to the Thrifty Female 
Hypothesis based on their reproductive strategy or inability to cache food during winter, but 
studies seeking to apply this hypothesis outside of bats are scarce.     
 
 
 
Figure 1. Conceptual diagrams of hypotheses predicting winter microclimate selection in cavernicolous 
bats. Each panel shows the hypothesized distribution of bats across a thermal gradient within a single 
hibernaculum (x-axis), which is expected to vary latitudinally (y-axis). The Colder is Better Hypothesis 
(A) posits that bats should select cold microclimates to maximize energy savings. The Hibernation 
Optimization Hypothesis (B) posits that bats should select microclimates that allow for survival while 
also reducing torpor expression. The Thrifty Female Hypothesis (C) posits that females should select 
colder microclimates than males because for females, fitness will be influenced not only by winter 
survival, but also emerging from hibernation with the fat stores needed for ovulation.  
 
 The latter two hypotheses reflect the importance of a range of thermal environments 
during winter. However, it is not well documented how available temperatures vary across large 
geographic areas, and how this variation affects hibernators. One such study, conducted across 
the unique temperature gradient present in Florida, demonstrates the potential impact of research 
 5 
in this area (McNab 1974). This study paired measurements of hibernacula microclimates 
available in Florida with observations of where gray myotis (M. grisescens) and tri-colored bats 
(Perimyotis subflavus) were found hibernating. Finding that the larger gray myotis was limited to 
northern Florida, where colder temperatures were available, McNab (1974) concluded that 
subtropical temperatures in Florida pose challenges to obligate hibernators, species in which 
females must hibernate to store sperm over winter. That the smaller tri-colored bat can be found 
hibernating at more southern latitudes in Florida reflects important differences in ecology or 
physiology, although the nature of that difference has not been tested. Thus, available 
temperatures vary with latitude, influencing opportunities for bats to reduce torpor use given 
their energetic constraints (Figure 1). This, in turn, may result in local adaptation and 
acclimatization in populations of species with large geographic ranges (Dunbar and Brigham 
2010). Unfortunately, few studies have examined variation in hibernacula temperatures across in 
North America and the potential for this to interact with selective pressures driving microhabitat 
selection, and more research is needed in this area.  
 Thus, research conducted in the nearly 50 years following Humphrey’s study of winter 
habitat selection in Indiana myotis has demonstrated the phenomenon is not the product of a 
single variable, but rather a collection of variables, with hibernators balancing costs and 
opportunities given limited energy. Viewed in this context, it is not surprising that winter habitat 
selection in well-studied species shows considerable variation. Unfortunately, the need for 
management recommendations on how to best provide, protect, and restore winter habitat is 
more pressing than ever, and extends to many more species. Below, we discuss how knowledge 
of factors behind winter habitat selection has been used in management in the past, how new data 
have challenged old assumptions, and how WNS has added an additional dimension to this 
challenge. 
 
3 Management Challenges 
 
When Humphrey presented his work in 1975, the newly minted Endangered Species Act directed 
agencies to avoid adversely affecting critical habitat. Humphrey noted that closing caves or 
obstructing their airflow was tantamount to their degradation or destruction, and recommended 
their restoration (Humphrey 1978). There are notable examples where these recommendations, 
when enacted, were followed by significant growth of winter populations (Richter et al. 1993; 
Tuttle and Kennedy 2002). While these successes were invaluable, it must be noted that not all 
such efforts have resulted in population responses, suggesting a fundamental disconnect between 
our understanding of hibernation ecology and population recovery. Indeed, unless the causes of 
population trends are clearly identified, management actions should not be expected to succeed 
(Figure 2). Given this disconnect, and the changing paradigm surrounding winter habitat 
selection, there clearly is a need to reconsider hibernacula management practices. Although all 
possible management actions merit attention, we focus our discussion solely on microclimates. 
 Restoration or improvements of thermal habitats within hibernacula revolves around 
efforts to reduce Ta (Richter et al. 1993; Tuttle and Kennedy 2002; Johnson et al. 2017). 
Unintended warming of hibernacula is well-known to occur at sites modified with walls and 
gates, which impede inflow of cold air during winter (Humphrey 1978; Richter et al. 1993). 
Restoration of airflow is straightforward in instances where large walls or doors meant to keep 
humans out impede airflow, but the impacts on bat populations are less straightforward than they 
may appear. Perhaps the most famous example comes from Wyandotte Cave, Indiana, where  
 6 
 
Figure 2. A flow-diagram depicting a list of possible causes for low abundance or 
species diversity at bat hibernacula, which may be an impetus for management actions. 
Because we lack a strong empirical connection between abundance and diversity within 
hibernacula (white-nose syndrome being an exception), management actions taken 
sometimes fail to address the underlying conservation concern and therefore fail to 
achieve the desired result. To illustrate this, we provide a flow diagram of the direct 
effects that three possible management actions would have given the underlying cause of 
low abundance or diversity at site, assuming these actions are implemented properly (e.g., 
gating did not change microclimates inadvertently). 
 7 
rapid growth of Indiana myotis occurred following removal of stone wall at the cave entrance 
(Richter et al. 1993). Although the cooling that occurred following manipulation was credited as 
leading to this growth, counts from nearby hibernacula suggest that Wyandotte was the recipient 
of bats moving in from nearby sites, including sites where microclimates were presumed more 
favorable (Brack et al. 2003). Most notably, the population at Twin Domes steadily declined 
following modification of Wyandotte, despite the hibernaculum having cooler Tas within the 
range of “preferred” temperatures (Richter et al. 1993; Tuttle and Kennedy 2002). Thus, while 
the cooling at Wyandotte improved conditions at the site, the movement of bats from even colder 
hibernacula clearly indicates that colder is not necessarily better. Furthermore, efforts to replicate 
results from Wyandotte at Great Scott Cave, Missouri, did not meet with population growth 
following the reopening of a blocked entrance to the site (Elliott and Clawson 2007).  
 Cooling hibernacula has, therefore, met with equivocal results. While this conservation 
strategy is likely effective in many cases, we urge caution when basing management solely on 
cooling hibernacula to supposed “optimal” temperatures. Such an approach is over-simplified 
and will not always lead to population recovery, as evidenced from the studies above and 
additional accounts of sites with suitable microclimates that go unused by bats (Gore et al. 2012). 
Perhaps more importantly, the two accounts reviewed above focused on a single species, which 
will not likely be inclusive of the needs of all cave-hibernating bats. This realization is essential 
for management at the time of this review, as one hibernating species, the northern myotis 
(Myotis septentrionalis) was recently listed as federally threatened, and additional species may 
follow as WNS continues to spread and cause mortality in affected areas. 
 Although restoring cool hibernacula Tas does not always result in population growth, 
limited evidence suggests that cooling unused hibernacula with warm Tas can improve otherwise 
unfavorable habitat. To our knowledge, the only published record of this comes from 
Pennsylvania, where state biologists created soil mounds to prevent cold air from flowing out of 
an abandoned mine with an entrance that slopes uphill (Johnson et al. 2017). Prior to the arrival 
of WNS, this effort to trap cold air in the mine resulted in an increase in the number of 
hibernating little brown myotis as well as an increasing species richness at the site. This example 
demonstrates how understanding factors determining Ta within a site (for review, see Perry 
2013) can be leveraged to improve marginal sites. However, we note that cooling hibernacula in 
this way comes from a southern perspective. In a survey of abandoned mines in Michigan’s 
Upper Peninsula, Kurta and Smith (2014) found that occupied sites were warmer than 
unoccupied sites, and lacked chimney-effect airflow other studies have found are important to 
other species at lower latitudes (Tuttle and Kennedy 2002). Kurta and Smith (2014) also found 
that occupied sites were more complex than unoccupied sites, and likely had a wider range of 
microclimates available than unoccupied sites as a result, although the authors did not report the 
amount of thermal diversity within the sites. Thus, while the importance of sites that are 
relatively warm or cold Tas may vary latitudinally, hibernacula offering a diversity of thermal 
habitats are likely of high value at all latitudes.  
 That hibernacula management is not as simple as maintaining and restoring cold Tas 
should not be surprising given bats’ need to balance the conflicting pressures described above. 
Unfortunately, WNS adds an additional variable to winter habitat selection and further 
complicates management. A full review of WNS is outside of the scope of this chapter, but its 
intersection with microhabitat selection and hibernacula management merits attention. The 
fungus causing WNS, Pseudogymnoascus destructans, has a temperature-dependent growth rate, 
growing optimally from 12.5–15.8 °C, with rapidly decreasing rates at colder and warmer 
 8 
temperatures (Verant et al. 2012). WNS mortality also varies with hibernacula Ta, with colder 
temperatures conferring a survival benefit (Langwig et al. 2012; Johnson et al. 2014; Lilley et al. 
2016). In addition to being associated with slower fungal growth, colder Tas likely benefit WNS-
affected bats because they promote increased use of torpor, providing energetic savings and 
limiting arousals and costly, potentially maladaptive, immune responses (Lilley et al. 2017).  
 WNS has therefore altered the costs and benefits of hibernating at the various Tas 
discussed above. Bats’ response to this change can be used to test the hypotheses shown in 
Figure 1, and potentially guide management. Specifically, a shift in habitat selection by both 
sexes towards colder Tas would broadly support the Hibernation Optimization Hypothesis, as 
bats would receive less benefit from minimizing torpor when suffering from WNS. Potentially 
more interesting, however, is whether females continue to select colder Tas than males, or if the 
effects of WNS are so great as to drive both sexes to similar microclimates. Finally, because the 
Colder is Better Hypothesis already predicts bats select cold Tas, it predicts no shift in habitat 
selection. Although data from WNS-positive hibernacula in Pennsylvania show remnant 
populations of little brown myotis, tri-colored bats, and big brown bats (Eptesicus fuscus) have 
responded to the disease by moving to colder areas within sites (Johnson et al. 2017), sex-
specific data have not yet been reported. 
 The shift in habitat selection by bats in response to WNS raises questions over how the 
need to increase short-term survival impacts long-term fitness. This question is a critical one, 
because although protecting cold hibernacula, or cooling those that are too warm, may yield 
short-term benefits for survival in WNS-affected areas (Johnson et al. 2017), hibernating at cold 
Tas comes at a physiological cost that bats should reduce where possible. It is for this reason that 
cooling hibernacula has met with mixed success in the past, and although the balance of costs 
and benefits to during hibernation has changed, the cost of cold Tas will still be incurred and 
potentially vex management efforts. We suggest that this realization, well supported in recent 
literature, be remembered in the years ahead. For example, if bats are hibernating at cold Tas in 
response to WNS, an important follow-up question is at what cost such an adaptation comes. 
Costly behavioral adaptations in response to invasive species have been documented elsewhere 
and are worthy of investigations in the context of WNS (Thawley and Langkilde 2017), although 
standing genetic variation and phenotypic plasticity may mitigate the process and contribute as 
population level pre-adaptations (Messer and Petrov 2013). Finally, because different species 
select different Tas during hibernation, and individuals do not necessarily show a consistent 
preference throughout winter, it is unlikely that narrow recommendations for hibernacula 
conditions will meet with success in the years ahead. Careful consideration of the life history of 
hibernators in an area, the availability of thermal habitats, and the costs and benefits of 
hibernating across this range of conditions, are needed if hibernacula management is to succeed 
in mitigating WNS mortality.  
 
4 Conclusion and Future Directions 
 
Winter is a complex and dangerous time for cavernicolous species. At temperate latitudes, many 
species appear to be obligate hibernators and often migrate not in search of warmer climates, but 
of suitable hibernacula. Hibernating bats are not dormant until spring, but are periodically active 
to copulate, minimize the physiological consequences of torpor, and to select appropriate 
microclimates. This habitat selection is driven by factors both internal (e.g., physiology) and 
external (e.g., availability) to hibernators, the interaction of which are not fully understood. Our 
 9 
review of what is known draws significantly on research presented and planned at the North 
American Symposium on Bat Research over the past 50 years, and illustrates a clear shift away 
from a conceptualizing hibernation as a simple process geared towards conservation of energy 
towards a dynamic period during which bats balance costs and opportunities given their limited 
energy reserves.  
 Unfortunately, the need to fill the remaining gaps in our knowledge of winter habitat 
selection has been made more urgent since the discovery of WNS. Carefully designed 
experiments are needed to better understand the causes and consequences of winter habitat 
selection of cave-hibernating species, and to determine how hibernacula management must be 
adapted in WNS-affected regions. Correlative studies, while valuable, are inherently limited in 
inferential scope and will never fully explain how conditions in hibernacula affect hibernating 
bats. In the absence of well-designed manipulative experiments, we run risk of once again 
viewing winter habitat selection one-dimensionally, only this time through the lens of WNS. For 
example, although selecting colder Tas may be adaptive for surviving infection with P. 
destructans, the fact that bats did not always select the coldest Tas prior to the arrival of WNS 
indicates that such an adaptation may also come at a cost. Moreover, a better understanding of 
winter ecology, including the use of alternative hibernacula is needed. Species such as the 
eastern small-footed (Myotis leibii) and northern myotis are suspected to hibernate in rock piles 
in addition to caves and mines, and even western populations of M. lucifugus are thought to rely 
on these sites not traditionally considered hibernacula (Lemen et al. 2016; Moosman et al. 2016; 
Neubaum 2018). This behavior is poorly understood but may be associated with different disease 
dynamics and require different management approaches than traditional hibernacula, and merits 
research attention.  
 When Humphrey presented his work on Indiana myotis in 1975, poor management of 
hibernacula temperatures and human disturbance were the greatest threats to North American 
bats during winter. Nearly 50 years later, the role of microclimate during winter remains a 
central focus of winter research and management. Bat researchers and managers today are faced 
with changing climates and the continued spread and impact of WNS. Successful management of 
winter habitats will require that these professionals avoid returning to our previous, over-
simplified understanding of winter habitat selection. To continue to grow our understanding on 
winter habitat selection, we recommend the use of experimental studies and investigations of the 
physiological, ecological, and fitness consequences of habitat selection at different Tas beyond 
energy conservation.  
 
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