Perimyotis Research Articles

Opportunistic Offshore Sighting of a Tricolored Bat (Perimyotis subflavus)

During a marine mammal vessel survey, a single Perimyotis subflavus (Tricolored Bat) was sighted 103.5 km off the coast of North Carolina. While we cannot determine whether the bat flew unaided from the mainland or stowed away on a ship, this is likely the furthest offshore sighting for the species. The possibility of Tricolored Bats flying offshore could have implications for wind-energy programs or other offshore industries.

Genetic Structure of the Vulnerable Tricolored Bat (Perimyotis subflavus)

The tricolored bat (Perimyotis subflavus) has experienced extensive declines in regional abundance — near 30% as of 2013 — due to disease, habitat loss, and anthropogenic conflict. There is urgency to determine whether the species should be protected in the United States; however, critical species-specific information required to make this decision is lacking. Here, we address those critical knowledge gaps by (i) estimating genetic diversity, and (ii) assessing population structure. We utilized sequence data from a 562 base pair region of the mitochondrial genome and eight autosomal microsatellite loci from 14 sampling locations across the core of P. subflavus' range and found substantial diversity in both data types. Further, we found contrasting patterns of population structure between the data types. Weak evidence for population structure was detected using the mitochondrial data, with the most probable population break dividing eastern and western sampling sites, and evidence for isolation-by-distance across the sampled region. Conversely, we detected no evidence for structure or isolation-by-distance using microsatellite data, revealing a panmictic population. The findings reported here represent a baseline understanding of genetic diversity and structure for P. subflavus; additional analyses using samples collected post white-nose syndrome emergence are required to understand losses in genetic diversity due to recent population declines.

Optimizing Surveys for Imperiled Bat Species Post White-Nose Syndrome

Many bat populations have plummeted in North America since the introduction of white-nose syndrome (WNS) in 2006, presenting challenges in researching population health and habitat use of affected species. Traditional survey techniques such as mist-netting and radio-telemetry have become increasingly time-consuming post-WNS due to the rarity of WNS-susceptible species in affected areas. To address the difficulty of studying imperiled bat species, we explored the use of an acoustic lure alongside mist-netting and acoustic monitoring to potentially enhance species detection in southeastern Missouri, United States. Acoustic lures elicit varying intra- and interspecific behavioral responses; thus, we explored the effects on multiple bat species' encounter rates while using tricolored bat Perimyotis subflavus distress vocalizations. The acoustic lure increased the number of acoustic detections for the federally endangered Indiana bat Myotis sodalis and non-imperiled big brown bat Eptesicus fuscus, and increased captures of the silver-haired bat Lasionycteris noctivagans, a species of conservation concern in Missouri. Additionally, only two individuals of P. subflavus were captured in mist-nets, and both were captured with the acoustic lure. These results suggested that acoustic lures are a valuable tool for identifying the presence of imperiled species when used in combination with mist-netting and acoustic detectors. Researchers studying bat communities that have experienced significant population declines because of WNS or other factors should incorporate multiple survey techniques, including acoustic lures, to increase capture rates and better document species distributions. Doing so should provide more accurate information on the distribution of imperiled bat species, which is relevant to conservation and management.

One model to rule them all: identifying priority bat habitats from multi‐species habitat suitability models

AbstractBats are important components of global ecosystems, providing essential ecosystem services with substantial economic benefit. Yet North American bat populations have been negatively affected by numerous factors (e.g., disease, habitat loss, wind energy development) with compounding effects. Bats use habitats at a variety of scales, from small, isolated patches to large, contiguous corridors. Landscape‐level research is necessary to identify important habitats, patches, and corridors to strategically target management interventions. We created habitat suitability models (HSMs) for hoary bats (Lasiurus cinereus), eastern red bats (L. borealis), and tri‐colored bats (Perimyotis subflavus) across Illinois, USA, using species‐specific landscape and climate variables. With the 3 models from this study and a previously published HSM for Indiana bats (Myotis sodalis), we stacked binary HSMs, thereby identifying priority conservation areas across Illinois. Species exhibited different distributional patterns and habitat preferences across Illinois. Multi‐species HSMs highlight high quality habitat (i.e., ecologically important habitat that provides preferred resources for roosting, foraging, and raising young) in southern Illinois and along river riparian areas. This approach identified priority conservation areas mainly following hydrologic zones, which allows managers to strategically target restoration and conservation measures, invest funds in habitat likely to have high return‐on‐investment, and assist with decisions that affect bats (e.g., siting wind turbines, purchasing mitigation lands).

A Survey of Bats at Lilley Cornett Woods Appalachian Ecological Research Station, Letcher County, Kentucky, before the Arrival of White-nosed Syndrome

Bat species associated with the Lilley Cornett Woods Appalachian Ecological Research Station (LCW) were documented over two field seasons. Mist netting was conducted during July 2009 [13 net nights], whereas acoustical monitoring was conducted from May–August 2010, with sampling occurring continuously for 85 nights. A total of 26 individuals, representing 5 species were captured: little brown bat (Myotis lucifugus; n = 11), tricolored bat (Perimyotis subflavus; n = 6), northern long-eared bat (Myotis septentrionalis; n = 6), big brown bat (Eptesicus fuscus; n = 2), hoary bat (Lasiurus cinereus; n = 1). There were 34,425 identified echolocation passes identifying 9 different bat species, i.e., tricolored bat, little brown bat, northern long-eared bat, big brown bat, Indiana bat (Myotis sodalis), gray bat (Myotis grisescens), eastern red bat (Lasiurus borealis), eastern small-footed bat (Myotis leibii), and evening bat (Nycticeius humeralis)]. Multiple species detected at LCW have been classified by the U.S. Fish and Wildlife Service (USFWS) as endangered (Indiana bat and gray bat) and threatened (northern long-eared bat). Since it was first detected, WNS has spread rapidly across North America and is associated with host mortality of >90%. We strongly recommend the Chiropteran community at LCW be resurveyed to assess the impacts of WNS, and that a passive acoustical monitoring program be developed and integrated into the area's long-term management plan.

Tricolored bats at a southern range edge exhibit partial migration northward in autumn

BackgroundAnimal migration is a widespread global adaptation by which individuals move in response to environmental conditions to reach more favorable conditions. For bats in temperate climates, migration and hibernation are often associated with each other when these bats must migrate to reach suitable overwintering sites. However, differences in movement across the geographical range of a species and the degree to which hibernation drives migratory behavior of bats in subtropical climates, where conditions may remain warm with available prey year-round, remains incomplete. Understanding the migratory strategies of subtropical bats during winter is of increasing importance as they are threatened by stressors such as disease and environmental change.MethodsWe evaluated migration patterns of tricolored bats (Perimyotis subflavus) in Florida, USA, through analysis of stable hydrogen isotope ratios of the fur. We inferred the summer geographic origins of the fur samples and estimated the minimum distance and likely direction traveled by hibernating individuals. We used linear models to examine whether hibernation region, colony size, and an individual’s sex affected the distance traveled.ResultsWe sampled 111 bats hibernating at 40 sites and found that more than half (54.1%) of individuals were residents of the area in which they hibernated. We found that almost half of the sampled bats (43.2%) traveled from southern Florida to overwinter in North Florida. We also documented three individuals that traveled > 100 km from northerly origins, one of which had traveled an estimated minimum distance of 1382 km. We also found that tricolored bats moved farther to reach hibernacula in Northwest Florida and hibernacula with more populous colonies, with no difference in movement between sexes.ConclusionsOur results indicate a pattern of northward autumnal movements of tricolored bats in the subtropical southeastern portion of their range. We suggest that bats are differentially constrained at the edge of their geographical range, resulting in movement contrary to what is expected. Even though we found that few (2.7%) bats moved into Florida from farther north, those migrants can potentially transfer the fungus that causes the deadly white-nose syndrome, which does not currently occur in the state. Our results support the characterization of tricolored bats as flexible partial migrators, with a rarely exercised capacity for long-distance movements.

Development of a multi-year white-nose syndrome mitigation strategy using antifungal volatile organic compounds.

Pseudogymnoascus destructans is a fungal pathogen responsible for a deadly disease among North American bats known as white-nose syndrome (WNS). Since detection of WNS in the United States in 2006, its rapid spread and high mortality has challenged development of treatment and prevention methods, a significant objective for wildlife management agencies. In an effort to mitigate precipitous declines in bat populations due to WNS, we have developed and implemented a multi-year mitigation strategy at Black Diamond Tunnel (BDT), Georgia, singly known as one of the most substantial winter colony sites for tricolored bats (Perimyotis subflavus), with pre-WNS abundance exceeding 5000 individuals. Our mitigation approach involved in situ treatment of bats at the colony level through aerosol distribution of antifungal volatile organic compounds (VOCs) that demonstrated an in vitro ability to inhibit P. destructans conidia germination and mycelial growth through contact-independent exposure. The VOCs evaluated have been identified from microbes inhabiting naturally-occurring fungistatic soils and endophytic fungi. These VOCs are of low toxicity to mammals and have been observed to elicit antagonism of P. destructans at low gaseous concentrations. Cumulatively, our observations resolved no detrimental impact on bat behavior or health, yet indicated a potential for attenuation of WNS related declines at BDT and demonstrated the feasibility of this novel disease management approach.

Roost Characteristics of a Tricolored Bat Perimyotis subflavus in the Missouri Ozarks

The tricolored bat (Perimyotis subflavus) once commonly occurred throughout the eastern and central United States, but is now experiencing range-wide population declines primarily due to white-nose syndrome and forest fragmentation. Conservation efforts for this species require more information regarding summer maternity roost characteristics, especially in the Ozark Highlands of Missouri, where the species has declined precipitously. Herein we report the capture and tracking of one female tricolored bat to two summer roosts in southeastern Missouri. Tree roosts differed by their substrates, as one was within a cluster of dead leaves on a snag and the other was located under exfoliating bark; otherwise, the roosts and surrounding vegetation were similar. Both roosts were located in large (>30 cm diameter breast height) oak (Quercus spp.) trees under a dense canopy of trees with similar basal areas. While our capture success was limited over two years, details regarding tricolored bat roost ecology are imperative for the species' conservation and management.

The influence of forest management practices on seasonal bat species occurrence and activity at the Kisatchie National Forest in Louisiana, USA

In the southeastern United States, where forests are the primary land cover type, understanding how forest stand characteristics and forest management practices influence bat distributions is critical for bat conservation and management. We deployed passive acoustic monitors to record bat calls at sites representing six forest types at the Kisatchie National Forest in central Louisiana during two winter (January–February 2020 and December 2020–February 2021) and two summer (June–August 2020 and 2021) periods. We also collected environmental data at the landscape and local scales to help explain patterns in bat species occurrence. We detected big brown bats (Eptesicus fuscus), eastern red/Seminole bats (Lasiurus borealis/L. seminolus), Myotis species, tricolored bats (Perimyotis subflavus), Mexican free-tailed bats (Tadarida brasiliensis), and hoary bats (Aeorestes cinereus) during both periods, and additionally detected evening bats (Nycticeius humeralis) during the summer. We observed seasonal differences in habitat use, and found that three bat species were more active during the summer in pine forests with group selection harvest, pine forests managed for red-cockaded woodpeckers (Leuconotopicus borealis), and pine forests that were clearcut within five years of our study when compared to unmanaged pine forests, thinned pine forests, and bottomland hardwood forests. Contrary to other studies, we found that the predicted probability of occupancy decreased with increasing proximity to riparian areas for four bat species, which could reflect the complex understory vegetation conditions that we observed along the riparian corridors in our study area. Our research identified forest characteristics and management practices that promote bat species diversity and activity in central Louisiana and demonstrated that pine forests with open understories and small openings in the canopy provide important foraging habitat for bats that occur in our study area and possibly other regions in the southeast.

Functional Redundancy in Bat Microbial Assemblage in the Presence of the White Nose Pathogen.

Understanding how host-associated microbial assemblages respond to pathogen invasion has implications for host health. Until recently, most investigations have focused on understanding the taxonomic composition of these assemblages. However, recent studies have suggested that microbial assemblage taxonomic composition is decoupled from its function, with assemblages being taxonomically varied but functionally constrained. The objective of this investigation was to understand how the Tri-colored bat, Perimyotis subflavus cutaneous microbial assemblage responds to fungal pathogen invasion within a functional context. We hypothesized that at a broad scale (e.g., KEGG pathways), there will be no difference in the functional assemblages between the white nose pathogen, Pseudogymnoascus destructans, positive and negative bats; and this pattern will be driven by the functional redundancy of bacterial taxa. At finer scales (e.g., gene models), we postulate differences in function attributed to interactions between bacteria and P. destructans, resulting in the production of antifungal metabolites. To test this, we used a combination of shotgun metagenomic and amplicon sequencing to characterize the bat cutaneous microbial assemblage in the presence/absence of P. destructans. Results showed that while there was a shift in taxonomic assemblage composition between P. destructans positive and negative bats, there was little overall difference in microbial function. Functional redundancy across bacterial taxa was clear at a broad-scale; however, both redundancy and variation in bacterial capability related to defense against pathogens was evident at finer scales. While functionality of the microbial assemblage was largely conserved in relation to P. destructans, the roles of particular functional pathways in resistance to fungal pathogens require further attention.

Changes in hibernating tricolored bat (Perimyotis subflavus) roosting behavior in response to white-nose syndrome.

Understanding animals' behavioral and physiological responses to pathogenic diseases is critical for management and conservation. One such disease, white‐nose syndrome (WNS), has greatly affected bat populations throughout eastern North America leading to significant population declines in several species. Although tricolored bat (Perimyotis subflavus) populations have experienced significant declines, little research has been conducted on their responses to the disease, particularly in the southeastern United States. Our objective was to document changes in tricolored bat roost site use after the appearance of WNS in a hibernaculum in the southeastern U.S. and relate these to microsite temperatures, ambient conditions, and population trends. We censused a tricolored bat hibernaculum in northwestern South Carolina, USA, once each year between February 26 and March 2, 2014–2021, and recorded species, section of the tunnel, distance from the entrance, and wall temperature next to each bat. The number of tricolored bats in the hibernaculum dropped by 90.3% during the first 3 years after the arrival of WNS. However, numbers stabilized and slightly increased from 2018 to 2021. Prior to the arrival of WNS, 95.6% of tricolored bats roosted in the back portion of the tunnel that was the warmest. After the arrival of WNS, we observed a significant increase in the proportion of bats using the front, colder portions of the tunnel, particularly during the period of population stabilization and increase. Roost temperatures of bats were also positively associated with February external temperatures. Our results suggest that greater use of the colder sections of the tunnel by tricolored bats could have led to increased survival due to slower growth rates of the fungus that causes WNS in colder temperatures or decreased energetic costs associated with colder hibernation temperatures. Thus, management actions that provide cold hibernacula may be an option for long‐term management of hibernacula, particularly in southern regions.

Emergence activity at hibernacula differs among four bat species affected by white-nose syndrome.

Prior to the introduction of white‐nose syndrome (WNS) to North America, temperate bats were thought to remain within hibernacula throughout most of the winter. However, recent research has shown that bats in the southeastern United States emerge regularly from hibernation and are active on the landscape, regardless of their WNS status. The relationship between winter activity and susceptibility to WNS has yet to be explored but warrants attention, as it may enable managers to implement targeted management for WNS‐affected species. We investigated this relationship by implanting 1346 passive integrated transponder (PIT) tags in four species that vary in their susceptibility to WNS. Based on PIT‐tag detections, three species entered hibernation from late October to early November. Bats were active at hibernacula entrances on days when midpoint temperatures ranged from −1.94 to 22.78°C (mean midpoint temperature = 8.70 ± 0.33°C). Eastern small‐footed bats (Myotis leibii), a species with low susceptibility to WNS, were active throughout winter, with a significant decrease in activity in mid‐hibernation (December 16 to February 15). Tricolored bats (Perimyotis subflavus), a species that is highly susceptible to WNS, exhibited an increase in activity beginning in mid‐hibernation and extending through late hibernation (February 16 to March 31). Indiana bats (M. sodalis), a species determined to have a medium–high susceptibility to WNS, remained on the landscape into early hibernation (November 1 to December 15), after which we did not record any again until the latter portion of mid‐hibernation. Finally, gray bats (M. grisescens), another species with low susceptibility to WNS, maintained low but regular levels of activity throughout winter. Given these results, we determined that emergence activity from hibernacula during winter is highly variable among bat species and our data will assist wildlife managers to make informed decisions regarding the timing of implementation of species‐specific conservation actions.

Changes in the Forest Bat Community After Arrival of White-Nose Syndrome in the Ouachita Mountains of Arkansas

Populations of some cave-hibernating bats have undergone declines in recent years due to an introduced fungus (Pseudogymnoascus destructans) that causes the disease white-nose syndrome (WNS), which is often fatal to bats during hibernation. Unprecedented declines in cave-hibernating species have the potential to change community composition via numerous mechanisms, including competitive release. We trapped bats for 6 years in the Ouachita Mountains of Arkansas prior to the arrival of WNS in the region and compared capture rates of 7 species to capture rates collected in 2020–2021 after WNS establishment. We found a 98% decline in Myotis septentrionalis (Northern Long-eared Bat) and a 77% decline in Perimyotis subflavus (Tricolored Bat) after WNS became prevalent. Nycticeius humeralis (Evening Bat) captures increased by 220% after WNS. Capture rates of Eptesicus fuscus (Big Brown Bat) increased by 100%, but this increase was not significant. We also found no significant differences in captures rates for Lasiurus borealis (Eastern Red Bat), Lasiurus seminolus (Seminole Bat), and Lasiurus cinereus (Hoary Bat) after the arrival of WNS. Our results indicate that the forest bat community of the Ouachita Mountains has been altered since the arrival of WNS in 2012, but it is unknown if these changes are permanent or if species will decline further or recover via adaptive or genetic changes in their populations in the future.

Habitat Associations of Overwintering Bats in Managed Pine Forest Landscapes

Research Highlights: Seasonal variation in environmental conditions coinciding with reproductive and energetic demands might result in seasonal differences in species-specific habitat use. We studied a winter assemblage of insectivorous bats and found that species acted as habitat generalists during winter compared to expectations based on the summer active season. Background and Objectives: In temperate regions, seasonal fluctuations in resource availability might restructure local bat assemblages. Initially perceived to only hibernate or migrate to avoid adverse winter conditions, temperate insectivorous bats appear to also employ intermediate overwintering strategies, as a growing body of literature suggests that winter activity is quite prevalent and even common in some lower latitude areas. However, to date, most studies have exclusively assessed habitat associations during summer. Because habitat use during summer is strongly influenced by reproduction, we hypothesized that habitat associations might differ during the non-reproductive winter period. We used acoustic monitoring to assess the habitat associations of bats across a managed pine landscape in the southeastern United States. Materials and Methods: During the winters of 2018 and 2019, we deployed acoustic detectors at 72 unique locations to monitor bat activity and characterized vegetation conditions at two scales (microhabitat and landscape). We used linear mixed models to characterize species-specific activity patterns associated with different vegetation conditions. Results: We found little evidence of different activity patterns during winter. The activity of three species (hoary bat: Lasiurus cinereus; southeastern myotis: Myotis austroriparius; and tricolored bat: Perimyotis subflavus) was not related to vegetation variables and only modest relationships were evident for four other species/groups (big brown bat: Eptesicus fuscus; eastern red bat: L. borealis; Seminole bat: L. seminolus; evening bat: Nycticeius humeralis; and Brazilian free-tailed bat: Tadarida brasiliensis). Conclusions: During winter, the bats in our study were active across the landscape in various cover types, suggesting that they do not exhibit the same habitat associations as in summer. Therefore, seasonal differences in distributions and habitat associations of bat populations need to be considered so that effective management strategies can be devised that help conserve bats year round.

ROADWAY-ASSOCIATED CULVERTS MAY SERVE AS A TRANSMISSION CORRIDOR FOR PSEUDOGYMNOASCUS DESTRUCTANS AND WHITE-NOSE SYNDROME IN THE COASTAL PLAINS AND COASTAL REGION OF GEORGIA, USA.

White-nose syndrome (WNS) is a disease among hibernating North American bats caused by the psychrophilic fungus Pseudogymnoascus destructans. Since its discovery in New York state, US, in 2006, and as of 2020, WNS has rapidly spread to 34 American states and seven Canadian provinces, causing precipitous declines of native bat populations across North America. The rapid spread of this fungal pathogen has been facilitated by the social behavior of bats, as well as the ability of subterranean hibernacula to support a favorable environment for P. destructans, and is probably exacerbated by anthropogenic transmission events. Although many bat species roost in natural cave environments, bats also selectively use diverse structures for hibernacula. Certain areas of the US lack caves, forcing bats to select different winter roosting environments. Bats have been observed using roadway-associated structures, such as bridges and culverts, for roosting, especially in regions that lack natural cave environments. However, the potential for P. destructans transmission in such roadway-associated structures requires further investigation. Understanding potential pathogen transmission in these widely used anthropogenic structures is crucial to disease management and preventing further declines of imperiled bat populations. Our study investigated these structures as potential pathogen transmission corridors by surveying the use of these structures by Perimyotis subflavus and other susceptible bat populations and by measuring their temperature. The results suggest the environments of roadway-associated culverts are thermally conducive to the proliferation of P. destructans-even in regions with mild winters-and the development of WNS in susceptible bat populations. It is apparent these roadway-associated structures have the potential to spread P. destructans and exacerbate the effect of WNS on susceptible bat populations.

Winter torpor expression varies in four bat species with differential susceptibility to white-nose syndrome

Studies examining the overwintering behaviors of North American hibernating bats are limited to a handful of species. We deployed temperature-sensitive transmitters on four species of bat that exhibit differences in their susceptibility to white nose syndrome (WNS; Myotis grisescens, M. leibii, M. sodalis, and Perimyotis subflavus) to determine if these differences are correlated with behavior exhibited during hibernation (i.e., torpor expression and arousal frequency). Mean torpor skin temperature (Tsk) and torpor bout duration varied significantly among species (P ≤ 0.024), but arousal Tsk and duration did not (P ≥ 0.057). One of the species with low susceptibility to WNS, M. leibii, had significantly shorter torpor bout durations (37.67 ± 26.89 h) than M. sodalis (260.67 ± 41.33 h), the species with medium susceptibility to WNS. Myotis leibii also had significantly higher torpor Tsk (18.57 °C ± 0.20) than M. grisescens (13.33 °C ± 0.60), a second species with low WNS susceptibility. The high susceptibility species, Perimyotis subflavus, exhibited low torpor Tsk (14.42 °C ± 0.36) but short torpor bouts (72.36 ± 32.16 h). We demonstrate that the four cavernicolous species examined exhibit a wide range in torpid skin temperature and torpor bout duration. Information from this study may improve WNS management in multispecies hibernacula or individual species management by providing insight into how some species may differ in their techniques for overwinter survival.

Biomarker Metabolites Discriminate between Physiological States of Field, Cave and White-nose Syndrome Diseased Bats.

Analysis of volatile organic compound (VOC) emissions using electronic-nose (e-nose) devices has shown promise for early detection of white-nose syndrome (WNS) in bats. Tricolored bats, Perimyotis subflavus, from three separate sampling groups defined by environmental conditions, levels of physical activity, and WNS-disease status were captured temporarily for collection of VOC emissions to determine relationships between these combinations of factors and physiological states, Pseudogymnoascus destructans (Pd)-infection status, and metabolic conditions. Physiologically active (non-torpid) healthy individuals were captured outside of caves in Arkansas and Louisiana. In addition, healthy and WNS-diseased torpid bats were sampled within caves in Arkansas. Whole-body VOC emissions from bats were collected using portable air-collection and sampling-chamber devices in tandem. Electronic aroma-detection data using three-dimensional Principal Component Analysis provided strong evidence that the three groups of bats had significantly different e-nose aroma signatures, indicative of different VOC profiles. This was confirmed by differences in peak numbers, peak areas, and tentative chemical identities indicated by chromatograms from dual-column GC-analyses. The numbers and quantities of VOCs present in whole-body emissions from physiologically active healthy field bats were significantly greater than those of torpid healthy and diseased cave bats. Specific VOCs were identified as chemical biomarkers of healthy and diseased states, environmental conditions (outside and inside of caves), and levels of physiological activity. These results suggest that GC/E-nose dual-technologies based on VOC-detection and analyses of physiological states, provide noninvasive alternative means for early assessments of Pd-infection, WNS-disease status, and other physiological states.

Experimental inoculation trial to determine the effects of temperature and humidity on White-nose Syndrome in hibernating bats

Disease results from interactions among the host, pathogen, and environment. Inoculation trials can quantify interactions among these players and explain aspects of disease ecology to inform management in variable and dynamic natural environments. White-nose Syndrome, a disease caused by the fungal pathogen, Pseudogymnoascus destructans (Pd), has caused severe population declines of several bat species in North America. We conducted the first experimental infection trial on the tri-colored bat, Perimyotis subflavus, to test the effect of temperature and humidity on disease severity. We also tested the effects of temperature and humidity on fungal growth and persistence on substrates. Unexpectedly, only 37% (35/95) of bats experimentally inoculated with Pd at the start of the experiment showed any infection response or disease symptoms after 83 days of captive hibernation. There was no evidence that temperature or humidity influenced infection response. Temperature had a strong effect on fungal growth on media plates, but the influence of humidity was more variable and uncertain. Designing laboratory studies to maximize research outcomes would be beneficial given the high costs of such efforts and potential for unexpected outcomes. Understanding the influence of microclimates on host–pathogen interactions remains an important consideration for managing wildlife diseases, particularly in variable environments.

Behavioural microclimate selection and physiological responses to environmental conditions in a hibernating bat

Hibernators adjust the expression of torpor behaviourally and physiologically to balance the benefits of energy conservation in hibernation against the physiological and ecological costs. Small fat-storing species, like many cave-hibernating bats, have long been thought to be highly constrained in their expression of hibernation because they must survive winter relying only on endogenous energy stores. We evaluated behavioural microclimate selection in tri-colored bats (Perimyotis subflavus (F. Cuvier, 1832)) across a 3-month hibernation experiment under laboratory conditions. We also opportunistically tested for evidence of acclimatization in torpid metabolic rate (TMR). When given access to gradients in microclimate, bats tended to choose the warmest temperature available (11 °C) while almost completely avoiding the driest condition available (85% relative humidity at 8 °C). Furthermore, bats held at different temperatures over the course of the hibernation showed no differences in TMR when measured under common conditions at the end of hibernation. Taken together, our results suggest that selective pressures to conserve energy during hibernation are not overwhelmingly strong and further support the proposition that optimal expression of hibernation is something less than the maximal expression of hibernation unless the animal is nearing starvation.

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

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.