Brown Myotis Research Articles

Changes in roosting decisions and group structure following parturition in little brown myotis (Myotis lucifugus)

In many temperate animals, reproductive cycles coincide with seasonal weather changes resulting in behaviour changes such as movement and habitat selection. In social species, these physiological and environmental changes can alter the costs and benefits of social interactions, impacting the structure of animal groups. In little brown myotis (Myotis lucifugus), a gregarious bat occupying much of North America, the pregnancy and lactation phases present different challenges to energy balance and maternal movement, and reduced forage distance has been observed during the lactation period. As such, we hypothesized that differences between reproductive phases alter the roost switching decisions of individual bats and therefore the overall group structure of little brown myotis maternity colonies. We observed that adult females were less likely to switch roosts during the lactation period even when accounting for changing weather conditions. This shift in roost switching behaviour may be the source of observed differences in group structure between reproductive periods. We reported a decline in network cohesiveness, but no meaningful variation in individual roost fidelity and association strengths of dyads between reproductive phases. These results support the contention that reproductive processes in female little brown myotis influence sociality and overall roosting patterns within maternity groups.

White adipose tissue remodeling in Little Brown Myotis (Myotis lucifugus) with white-nose syndrome.

White-nose syndrome (WNS) is a fungal wildlife disease of bats that has caused precipitous declines in certain Nearctic bat species. A key driver of mortality is premature exhaustion of fat reserves, primarily white adipose tissue (WAT), that bats rely on to meet their metabolic needs during winter. However, the pathophysiological and metabolic effects of WNS have remained ill-defined. To elucidate metabolic mechanisms associated with WNS mortality, we infected a WNS susceptible species, the Little Brown Myotis (Myotis lucifugus), with Pseudogymnoascus destructans (Pd) and collected WAT biopsies for histology and targeted lipidomics. These results were compared to the WNS-resistant Big Brown Bat (Eptesicus fuscus). A similar distribution in broad lipid class was observed in both species, with total WAT primarily consisting of triacylglycerides. Baseline differences in WAT chemical composition between species showed that higher glycerophospholipids (GPs) levels in E. fuscus were dominated by unsaturated or monounsaturated moieties and n-6 (18:2, 20:2, 20:3, 20:4) fatty acids. Conversely, higher GP levels in M. lucifugus WAT were primarily compounds containing n-3 (20:5 and 22:5) fatty acids. Following Pd-infection, we found that perturbation to WAT reserves occurs in M. lucifugus, but not in the resistant E. fuscus. A total of 66 GPs (primarily glycerophosphocholines and glycerophosphoethanolamines) were higher in Pd-infected M. lucifugus, indicating perturbation to the WAT structural component. In addition to changes in lipid chemistry, smaller adipocyte sizes and increased extracellular matrix deposition was observed in Pd-infected M. lucifugus. This is the first study to describe WAT GP composition of bats with different susceptibilities to WNS and highlights that recovery from WNS may require repair from adipose remodeling in addition to replenishing depot fat during spring emergence.

Heterogenous effects of bat declines from white‐nose syndrome on arthropods

AbstractIn North America, white‐nose syndrome (WNS) has caused precipitous declines in hibernating bat populations, raising the question of whether the rapid loss of arthropodivorous bats may affect the abundance of their prey. During the summers of 2015–2018 (1 year after the arrival of WNS in Wisconsin, USA), we performed intensive arthropod black‐light trapping, ultrasonic acoustic monitoring, and emergence counts at 10 little brown (Myotis lucifugus) and big brown (Eptesicus fuscus) bat maternity roosts with paired control sites. For little brown bats, which are severely affected by WNS, roost counts declined by 95% over the four‐year period, compared to a 38% decline in big brown bat roost counts. Total arthropod abundance decreased by 49%, although decreases among common little brown bat prey were less severe. Our natural predator exclusion experiment supports existing evidence that bats can have measurable trophic impacts on arthropod communities, primarily via top‐down effects on common prey.

Preference for hibernacula microclimates varies among 3 bat species susceptible to white-nose syndrome

Abstract North American bat populations have experienced precipitous declines since the introduction of white-nose syndrome (WNS). Evidence that bats have responded to WNS by altering their winter habitat selection has been used to manipulate underground environments and improve winter survival. However, such management practices must be based on local data, which do not exist for all regions. Our goal was to identify determinants of winter habitat use for 3 bat species with varying susceptibility to WNS. To do so, we conducted 188 surveys of 129 potential hibernacula over 3 winters. We found that the range of winter temperatures and presence of water were important for the Little Brown Myotis (Myotis lucifugus) and Tricolored Bat (Perimyotis subflavus), species that are highly susceptible to WNS. Counts of both species were greater in sites with a narrow (<5 °C) temperature range and where streams or water bodies >25 m2 were present. In addition, we found larger groups of Little Brown Myotis in abandoned railroad tunnels than in caves. Winter counts of these species increased over time at 3 railroad tunnels that were surveyed for 3 consecutive winters, whereas populations were extirpated from historically important caves and mines. Counts of Big Brown Bats (Eptesicus fuscus), which are less susceptible to WNS, were also greater in hibernacula with water bodies. However, average winter temperature also helped predict counts of Big Brown Bats. This species had a curvilinear response to temperature, with most bats found at hibernacula with average winter temperatures of 4 to 6 °C, and fewer bats observed at warmer and colder conditions. These data show that focusing solely on historically important hibernacula may fail to achieve conservation goals for the Little Brown Myotis and Tricolored Bat in our region, and suggest that anthropogenic structures can provide habitat for remnant populations of imperiled bat species.

Characterizing diurnal roosts of male Little Brown Myotis (Myotis lucifugus) during summer

Abstract Shelter is one critical aspect of an animal’s habitat, providing refuge from predators and weather, protection for offspring, and aiding in physiological homeostasis. During the day, bats find shelter in roosts—spaces created under tree bark, in tree cavities, or between rocks—after spending the night searching for food. Finding a roost with a microclimate that enables bats to remain in their thermoneutral zone could reduce energetic demands or allow bats to allocate energy to other activities such as reproduction and fighting disease. We aimed to characterize the structural features and microclimate (i.e., temperature) of roosts used by male Little Brown Myotis (Myotis lucifugus) during the summer and determine whether bats select certain characteristics disproportionally to what is available at different spatial scales. During the summers of 2017 and 2018, we radio-tracked 34 male M. lucifugus in Lodgepole Pine-dominated forests. We located at least 1 roost for 20 individuals (average = 2.85 roosts/bat, range = 1 to 6). Although snags were available, most of the roosts were in rock features (86% in rocks, 14% in trees or snags). Male M. lucifugus were more likely to select rock roosts with less canopy closure that were closer to water compared to available roosts on the landscape. They also selected roosts in rock features occurring within larger areas of rock cover that had wider entrances and access to crevices that faced the sky; these roosts also had warmer microclimates relative to other locations available on the landscape. Crevices that allow the bat to bask in the sun and change locations within a roost, minimizing energy needed for active thermoregulation, could be very beneficial for individuals recovering from diseases such as white-nose syndrome. Our work indicates that rock features provide habitat for male M. lucifugus during summer; other studies have shown that bats roost in these features during autumn and winter, further supporting their importance. By protecting these important rock structures, managers can help bats meet their habitat needs throughout the year.

Using PIT tags to infer bat reproductive status and parturition date: busy nights during lactation

Abstract Passive integrated transponders (PIT tags) can aid in the collection of important demographic data for species for which other methods, such as GPS technology, are not suitable. PIT tags can be particularly suitable to monitor small and cryptic species like bats and permit inference on their behavioral ecology. Literature for several species of bats states that females change their nightly activity patterns—going out and in of the roost only once per night during gestation compared to several times during lactation. Hence, we tested whether PIT tag detection patterns could be used to infer reproductive status and parturition date of female bats. From 2017 to 2021, we recorded detections of PIT-tagged little brown (Myotis lucifugus) and northern long-eared bats (M. septentrionalis) at the entrance of 2 maternity roosts in Québec and Newfoundland, Canada. We also used the maternity roost in Québec as a case study to further evaluate the potential of this method to link behavior and demography and investigated factors affecting parturition date. We were able to infer reproductive status for 63% to 97% of tagged individuals detected during both the gestation and the lactation periods, and parturition date for 61% to 95% of reproductive individuals, depending on the year and roost. Early spring arrival at the roost and warm spring mean temperature at night were associated with earlier parturition dates. Herein, we highlight that PIT tag systems may be useful to detect changes in activity patterns of female bats and infer individual reproductive parameters, which is on the long-term less stressful for bats and easier for researchers. We demonstrate that this approach is useful to investigate intrinsic and extrinsic factors of reproductive parameters, improving our understanding of bat population dynamics resulting in more informed population management decisions.

Seasonal phenology of the little brown bat (Myotis lucifugus) at 60° N

AbstractTo investigate the impact of short summers and long summer solar periods at high latitudes on the behavior of a nocturnal, hibernating mammal, we recorded the phenology of Myotis lucifugus (little brown myotis) at 60° N in the Northwest Territories (NWT), Canada. In particular, we assessed the timing of spring emergence from, and autumn entry into, hibernation, reproduction, and seasonal mass fluctuations. We used a combination of acoustic monitoring and capture surveys at two hibernacula and two maternity roosts during 2011 and 2012. Myotis spp. were active at the hibernacula from late April to late September/early October, suggesting that the “active” season length is similar to that of populations farther south. At maternity colonies, we detected M. lucifugus activity from early May to early October, with peaks during mid‐July in both years. Lactation, fledging, and weaning all occurred later in the NWT than at more southern locations, and reproductive rates were significantly lower than rates observed farther south. The average mass of individuals fluctuated throughout the season, with an initial decline immediately following emergence from hibernation likely reflecting increased energy expenditure due to flight and decreased use of torpor, coupled with relatively low prey intake due to low prey abundance associated with cool temperatures. Females did not appear to have lower pre‐hibernation masses than those in more southern populations, suggesting that despite the cool spring and autumn temperatures, and short summer nights, bats are able to obtain enough energy for reproduction and mass accumulation for hibernation. However, the lower reproductive rates may indicate that there are limitations to life at the northern limits of the species' range.

Co-roosting relationships are consistent across years in a bat maternity group

Long-lived, group living animals have the potential to form multiyear relationships. In some temperate bat species, maternity groups break apart and rejoin both daily, as females depart to forage and select day roosts to use, and annually, as bats leave for and return from hibernation. Here, we investigated whether bats have persistent social preferences by testing whether relationships between dyads in a focal year could be predicted by previous years. We also hypothesized that experience influences social preferences and predicted that an individual’s age would influence its network position, while familiarity with bats of the same cohort would drive persistent social preferences. We quantified roost co-occurrence in little brown myotis (Myotis lucifugus) in Salmonier Nature Park, Newfoundland, Canada both within and among years. We found that roost co-occurrence patterns of previous years still had predictive value even when accounting for potential roost fidelity. However, we found no evidence that cohort familiarity or age explained any of the variation. Overall, we found long-term patterns of association in this temperate bat species that suggest levels of social complexity akin to other large mammal species.

Sampling Duration and Season Recommendations for Passive Acoustic Monitoring of Bats after White-Nose Syndrome

Abstract Since 2006, white-nose syndrome has caused drastic declines in populations of several hibernating bat species throughout eastern North America. Thus, there is a growing need to establish long-term monitoring programs to assess changes in bat populations over time. Information on the seasonal timing of species occurrence and the sampling effort required to acoustically detect individual bat species and obtain complete inventories will enable researchers to design and implement more effective monitoring programs. From April to October 2018 to 2021, we passively sampled for bats using full-spectrum detectors at eight permanent sites at Fort Indiantown Gap National Guard Training Center, Pennsylvania. We examined seasonal activity patterns and estimated bat species richness among sites and seasons using species accumulation curves. We also estimated probability of detection (p) and site occupancy (Ψ) using single-season occupancy models in PRESENCE software and then determined the minimum number of sampling nights needed to reliably infer the absence of each species. We identified 286,131 bat passes of eight species in 4,107 detector-nights. Seasonal patterns of activity varied among species. We needed approximately 20 sampling nights to detect 90% of the total bat species richness among sites, and we needed 4 to 10 nights to detect 90% of species richness among seasons. We needed relatively few nights (≤12 nights) to detect most species during summer; however, we needed many more nights to detect acoustically rare species. Our results indicate that the acoustic sampling effort currently required to determine the presence or probable absence of Indiana myotis Myotis sodalis, northern long-eared myotis M. septentrionalis, and tricolored bats Perimyotis subflavus during summer may not be adequate for these species in some areas and that a considerable level of effort (>40 nights) is needed to detect little brown myotis M. lucifugus. Monitoring programs that incorporate efficient sampling methodologies will be critical for future conservation efforts as populations of several bat species continue to decline.

Landscape predictors and spatial distribution of little brown myotis (Myotis lucifugus) coastal foraging habitat along the Northern Gulf of Alaska

Landscape predictors and spatial distribution of little brown myotis (Myotis lucifugus) coastal foraging habitat along the Northern Gulf of Alaska

Individual Variation in Parturition Timing within and among Years for a Bat Maternity Colony.

In monoestrous species, the timing of reproduction can have important impacts on offspring survival. For heterotherms in temperate areas, parturition timing is constrained by cold weather survival strategies, such as hibernation and torpor. Female bats that are year-round residents of temperate regions, such as little brown myotis (Myotis lucifugus), invest significantly in parental care resulting in sharp changes in behavior immediately following parturition. These behavior changes may include increases in nighttime roost revisits, which can be used to identify parturition dates for individual bats that have been passive integrated transponder (PIT) tagged and use monitored roosts. Using a system of tagged bats and monitored roosts in Pynn's Brook and Salmonier Nature Park Newfoundland, Canada, we estimated parturition dates for 426 female M. lucifugus in at least one year, based on changes in nighttime roost revisit patterns, and quantified the variation in parturition dates within years among individuals, and within individuals among years. Overall, we report on a wide variation in parturition dates within years among individuals as well as year-to-year variations, both across the population and within individuals. Spring weather conditions appeared to be important influences on parturition timing. Changes in spring and summer temperature and extreme weather events, as expected due to ongoing climate change, may impact parturition timing, and therefore, offspring survival of temperate bats.

Myotis Roost Use Is Influenced by Seasonal Thermal Needs

Abstract Reproductive bats switch frequently among roosts to select the most advantageous microclimates and avoid predation or parasitism. Many bats use human-made structures, such as bat boxes and buildings, in areas where natural structures are less abundant. Artificial structures, which may be warmer and larger than natural structures, may affect bat behavior and roost use. We studied Yuma Myotis (Myotis yumanensis) and Little Brown Myotis (M. lucifugus) in artificial structures at two sites to understand how roost conditions and reproductive pressures influenced roost switching in maternity colonies in the lower mainland of British Columbia, Canada. During summer 2019, we used Passive Integrated Technology (PIT tags and scanners) to track daily roosting locations of individuals. Yuma myotis and little brown myotis used at least five roosts at each site and switched almost daily among roosts. Bats were less likely to switch from roosts that were 25–42°C and switch roosts during lactation, particularly when the young were nonvolant. Our findings suggest that reproductive female myotis that use artificial roosts seek out warm roosts to limit energy expenditure and speed up offspring development. We also found that bats boxes were not thermally stable environments and the behavior of bats reflected temperature variability. Land managers should ensure that multiple nearby roosts are available to maternity colonies, as reproductive bats require a range of temperatures and roost types during summer.

Environmental control reduces white‐nose syndrome infection in hibernating bats

AbstractInfectious diseases caused by invasive, environmentally persistent fungal pathogens have increasingly endangered global biodiversity, yet disease management remains a major conservation challenge. A prominent example is white‐nose syndrome (WNS), a disease caused by the invasive fungal pathogen Pseudogymnoascus destructans (Pd) that has devastated populations of multiple North American bat species, but for which few effective management tools exist. Here, we propose that strategies to delay environmental transmission of Pd during early winter could limit WNS disease effects across winter, benefitting bats. We used a small captive experiment and a multi‐year field trial on wild, free‐ranging bats to assess an environmental control strategy to manage Pd within its environmental reservoir in Pennsylvania, USA, where the pathogen has become endemic. The strategy centers on the application of Polyethylene Glycol 8000 (PEG) to roost substrates in summer, prior to bat hibernation, as a means to disrupt environmental transmission to bats in early winter. In the captive experiment, environmental transmission of Pd to immunologically naïve little brown myotis (Myotis lucifugus) occurred from roost substrates inoculated with Pd, but the application of PEG to these substrates effectively blocked this transmission. In the field trial, Pd load and infection extent both declined substantially in free‐ranging M. lucifugus after treatment relative to controls, with declines exceeding effects of inter‐site and inter‐annual variation. Pathogen prevalence and load also declined substantially after PEG treatment in big brown bats (Eptesicus fuscus). No negative effects of PEG treatment were observed in body condition or colony counts of bats or in the microbial community. Together, these results are consistent with effective environmental control of Pd and reduced WNS disease effects in bats within contaminated hibernacula. The results also highlight the potential of carefully designed environmental control strategies for managing environmentally persistent pathogens.

Little brown Myotis roosts are spatially associated with foraging resources on Prince Edward Island

AbstractAnimal fitness is closely linked to accessing and capitalizing on local resources such as prey and shelter. Resources vary in quality, thus individuals may demonstrate selectivity for particular resource types. We examined resource selection in roost selection patterns of temperate bats on Prince Edward Island. To complement existing work examining roost structural characteristics, we evaluated whether roost selection by little brown myotis (Myotis lucifugus) could be explained by landscape characteristics. Given a sample of roosts identified through radio telemetry, community reports and a randomly selected sample of comparison structures, we determined that a combination of proximity to forest and open wetland best explained roost selection. Roost selection appears to reflect the optimization of time and energy budgets, and the proportion of maternity roosts within the sample suggests that these constraints may be more acute in reproductive females. Given the importance of roosts for reproductive success in females, future work should seek to quantify the role of physical characteristics on roost structure selection and the preservation of suitable roosting structures.

SUN HATS FOR BAT BOXES: MITIGATING THE RISK OF OVERHEATING AT NORTHERN LATITUDES

At northern latitudes, bats often use roosting structures provided by people. Conventional thinking suggests that bat boxes should be entirely black to absorb heat and assist bats with thermoregulation. However, with long periods of summer daylight in subarctic Canada, we suspected that risk of overheating might occur in black boxes. We investigated whether roost temperatures exceeded 42°C, the upper limit of the thermoneutral zone in Little Brown Myotis (Myotis lucifugus), and whether replacing the black roof with a white one, akin to a sun hat, would alleviate the risk of overheating without compromising roost temperatures especially at night. We also investigated whether bats used the boxes. The internal temperature of black boxes exceeded 42°C on some days in 2 summers. Substituting the black roof with a white one consistently reduced the maximum daily roost temperature to below 42°C, but this was also accompanied by a slightly lower minimum roost temperature at night and a cooler roost temperature regime overall. The reduction in maximum daily roost temperature by the white roof was more pronounced on days with higher maximum daily ambient temperatures. At 5 sites with paired white-roof and black-roof boxes, 4 had bat use of both boxes and 1 had no use of either box. Bats used 10 of 19 (53%) black-roof boxes in 2019, and 16 of 21 (77%) in 2020. Replacing a black roof with a white one can mitigate risk of overheating for boxes in subarctic latitudes, and likely through a range of temperate latitudes. However, completely black boxes are still necessary to enhance the thermal environment for roosting bats through most of the summer. We suggest that providing bats with roosting options, such as paired black-roof and white-roof boxes immediately adjacent to one another, is a better habitat enhancement option than just single black boxes.

Roost fidelity partially explains maternity roosting association patterns in Myotis lucifugus

Resources that draw individuals to a specific location may result in the formation of groups and development of individual social preferences. Simultaneously considering both ecological and social factors can therefore reveal underlying mechanisms of group formation and organization. Females of some temperate bat species roost in groups during the spring and summer months within which they give birth to and nurse their pups. Females switch roosts frequently, but the factors that influence roost switching remain poorly understood. To characterize the structure of a bat maternity group and gather evidence for the role of social preference in shaping this structure, we used roost co-occurrence data from little brown myotis, Myotis lucifugus , implanted with passive integrated transponder tags and roost boxes monitored with passive readers in Salmonier Nature Park, Newfoundland, Canada. By developing informed null models, we more directly investigate hypotheses that may explain why bats roost together. Although our results suggest that association patterns of maternity groups can largely be explained by similar interindividual patterns in bats' roosting frequencies within a given roost box (roost fidelity), other factors are likely to contribute to the observed structure. We thus provide support for the potential influence of roost and social preferences in shaping maternity group structure. • Female bats frequently switch roosts, changing who they roost with each day. • Some bats did not roost together at frequencies expected by chance. • Other bats occasionally roosted together more than expected by chance. • Social preferences may be important in influencing roosting decisions.

Active season body mass patterns of little brown and northern myotis bats.

Animals are expected to adjust their behavioral patterns to improve fitness outcomes, such as fecundity or offspring survival. For long-lived hibernators, decisions made in each annual cycle may reflect considerations not just for concurrent survival and reproduction but also the pressure to maximize overwinter survival and future reproductive success. We examined how these elements manifest themselves in the body mass variation patterns of North American northern latitude temperate bats, whose size and roosting habits present considerable monitoring challenges. We characterized and compared the summer and fall mass variation patterns of little brown myotis (Myotis lucifugus) and northern myotis (M. septentrionalis) from a historic dataset. In summer, the estimated date of parturition was strongly associated with spring foraging conditions (low wind, low precipitation, and warm temperatures), and mass gain associated with female reproduction conferred considerable differentiation between the mass variation patterns of females and males. In fall, differences were most apparent among species, although adults exhibited a greater capacity for rapid mass gain than juveniles. These results demonstrate how reproductive constraints and interannual survival have important influences on the behavior of temperate bats. Future work should seek to quantify the fitness benefits of patterns identified in this study, such as the rate of prehibernation mass gain.

A male Little Brown Myotis (<i>Myotis lucifugus</i>) recaptured after 28 years at the same site in southwest Saskatchewan, Canada

Little Brown Myotis (Myotis lucifugus) is one of the most common and widely distributed mammals in Canada and has been recorded to live over 30 years in the wild. As part of a long-term bat research project in Cypress Hills Interprovincial Park, Saskatchewan, we recaptured a male Little Brown Bat in a mist net over Battle Creek on 12 June 2021. The bat was recaptured within 100 m of where it was first captured and banded as an adult in 1993, indicating that this bat was at least 29 years old and exhibited repeated use of the same summer flying, foraging, and drinking site. The bat was not caught in the intervening years; therefore, its frequency of use of this site is unknown. In eastern North America, this species has declined because of high mortality rates associated with White-nose Syndrome (WNS). WNS has been moving westward and has now been detected in eastern and western Saskatchewan. Understanding aspects of the natural history of Little Brown Bat, including longevity, is important before WNS is detected in a region and leads us to advocate continued marking of individuals (e.g., banding, PIT tagging) to continue learning about bat longevity and survival before and after WNS infection.

Rapidly declining body size in an insectivorous bat is associated with increased precipitation and decreased survival.

Reduced food availability is implicated in declines in avian aerial insectivores, but the effect of nutritional stress on mammalian aerial insectivores is unclear. Unlike birds, insectivorous bats provision their young through lactation, which might protect nursing juveniles when prey availability is low but could increase the energetic burden on lactating females. We analyzed a 15-year capture-mark-recapture data set from 5312 individual little brown myotis (Myotis lucifugus) captured at 11 maternity colonies in northwestern Canada, to test the hypothesis that nutritional stress is impacting these mammalian aerial insectivores. We used long-bone (forearm [FA]) length as a proxy for relative access to nutrition during development, and body mass as a proxy for access to nutrition prior to capture. Average FA length and body mass both decreased significantly over the study period in adult females and juveniles, suggesting decreased access to nutrition. Effect sizes were very small, similar to those reported for declining body size in avian aerial insectivores. Declines in juvenile body mass were only observed in individuals captured in late summer when they were foraging independently, supporting our hypothesis that lactation provides some protection to nursing young during periods of nutritional stress. Potential drivers of the decline in bat size include one or both of (1) declining insect (prey) abundance, and (2) declining prey availability. Echolocating insectivorous bats cannot forage effectively during rainfall, which is increasing in our study area. The body mass of captured adult females and juveniles in our study was lower, on average, after periods of high rainfall, and higher after warmer-than-average periods. Finally, survival models revealed a positive association between FA length and survival, suggesting a fitness consequence to declines in body size. Our study area has not yet been impacted by bat white-nose syndrome (WNS), but research elsewhere has suggested that fatter bats are more likely to survive infection. We found evidence for WNS-independent shifts in the body size of little brown myotis, which can inform studies investigating population responses to WNS. More broadly, the cumulative effects of multiple stressors (e.g., disease, nutritional stress, climate change, and other pressures) on mammalian aerial insectivores require urgent attention.

Population sizes and activity patterns of little brown myotis in Yellowstone National Park

AbstractThe spread of white-nose syndrome into western North America has caused concerns that bat species inhabiting the region will soon experience population declines like those seen to the east. However, much of the region lacks baseline estimates of abundance for bats believed to be susceptible to WNS due to a scarcity of known hibernacula, where populations are traditionally monitored. The goal of this study was to determine the abundance, roost fidelity, and activity patterns of summer colonies of female little brown myotis (Myotis lucifugus) in an area with no known hibernacula. To accomplish this, we subcutaneously implanted passive integrated transponder (PIT) tags into 297 female little brown myotis from 2015 to 2018 and installed radio-frequency identification (RFID) readers and antennas inside three maternity roosts in Yellowstone National Park. Bats occupied RFID-monitored roosts on 32% of days and were never detected at maternity roosts located > 16 km from where they were tagged. Roost fidelity varied throughout summer and was greatest during late gestation and early lactation. This allowed us to combine nightly scans of RFID-tagged bats with visual emergence counts to estimate the population of bats using two roosts located >16 km apart during 2017–2018. Population estimates of both colonies were markedly higher (N* = 208 ± 6 bats and N* = 836 ± 67 bats during 2018) than the number of bats seen during evening emergence (high counts of 127 and 222, respectively). Nocturnal visits of tagged bats to these roosts increased around the time of parturition, indicative of bats returning to nurse young. These data show that emergence count and PIT tag data can be combined to monitor bat population abundance and activity patterns in areas where hibernacula are absent or where their locations are unknown.