Brown Myotis Research Articles

ROOST CHARACTERISTICS OF BATS IN THE PINE RIDGE REGION OF NEBRASKA

Protecting day roosts is imperative to the persistence and survival of local populations of tree-roosting bats. The Pine Ridge region of Nebraska represents the largest area of coniferous forests in the state and possesses the greatest diversity of bats in Nebraska. In this study, we examined roost characteristics primarily for 4 species in need of conservation in the region: Fringed Myotis (Myotis thysanodes), Long-legged Myotis (Myotis volans), Little Brown Myotis (Myotis lucifugus), and Hoary Bat (Aeorestes cinereus). With a limited understanding of roost characteristics for other species in the region, we also collected some roost data for the Big Brown Bat (Eptesicus fuscus) and Western Small-footed Myotis (Myotis ciliolabrum). We tracked 42 bats with an emphasis on lactating females. Fringed Myotis, Big Brown Bats, and Western Small-footed Myotis typically roosted in cracks and crevices of dead trees. Long-legged Myotis roosted only in rock crevices at our western-most study site and only large, dead Ponderosa Pines (Pinus ponderosa) at our eastern-most site. Little Brown Myotis roosted in human-made structures in large colonies. Hoary Bats roosted in foliage of live hardwoods and conifers. Conservation of dead Ponderosa Pines, particularly those with large diameters and exfoliating bark, will provide roost structures for most crevice-roosting bats in the region. Our limited data for Hoary Bats suggest that roost-tree use is variable, as individuals roosted in both live hardwoods and conifers. Exclusive use of buildings throughout the region by female Little Brown Myotis implies timber harvests and wildfires might not greatly affect roosts for reproductive females. We demonstrated that roost characteristics vary among species and between nearby populations of the same species, representing important information for making informed habitat management decisions in a region with limited forests in northwestern Nebraska.

LITTLE BROWN MYOTIS ACTIVITY PATTERNS IN SOUTH-CENTRAL ALASKA

In this study, we investigated how Little Brown Myotis (Myotis lucifugus), North America's northernmost bat species, adjusted to variable spring and autumn conditions and very little darkness during the boreal summer. We recorded bat activity around Anchorage and the lower Matanuska-Susitna Valley, Alaska. Initiation of bat activity in the spring varied among years and was affected by minimum nightly temperatures in late April and, to a lesser extent, precipitation. Cessation of bat activity in the autumn was consistent among years, with a weak association with early-October minimum temperature. During summer, bat activity was highest on warm, clear nights, but was reduced by wind or rain. Bat activity was positively related to open water and forest cover and negatively related to human development. Most bat activity occurred between sunset and sunrise, even during very short nights in mid-summer. Although there was some activity prior to sunset, bat activity after sunrise was very rare. Pre-sunset bat activity was almost exclusively at sites with high forest cover. After sunset, moderately forested sites were also used, but sites with little forest cover were rarely used before or after sunset.

Capture Rate Declines of Northern Myotis in the Canadian Maritimes

ABSTRACTThe disease white‐nose syndrome (WNS) has caused widespread decline of North American bat species. Species like little brown myotis (Myotis lucifugus) have received more attention than others, such as northern myotis (Myotis septentrionalis). We were concerned that management decisions based on the demographic condition of little brown myotis may be inappropriate for northern myotis due to the potential for variation in species‐specific responses to WNS. We therefore compiled capture data from Canada's Maritime provinces collected between 2003 and 2019 to identify if disparate population trends exist between the 2 species. We identified a decline in northern myotis capture‐per‐unit‐effort (CPUE) after the detection of WNS (hereafter, post‐WNS), in each study region and a divergence from the historic CPUE ratio between the 2 species. Whereas 380 northern myotis were captured pre‐WNS, only 4 were captured post‐WNS. The pre‐WNS ratio of northern myotis to little brown myotis CPUE in New Brunswick, Prince Edward Island, and Nova Scotia declined from 0.541, 0.273, and 0.291 to 0.046, 0, and 0 respectively, post‐WNS. Our results indicate that northern myotis populations in the Maritimes have experienced a serious decline. Standardized and systematic capture surveys should be conducted at summer roosting areas and swarming sites in combination with counts in hibernacula to clarify the current distribution, population size, and resource selection patterns of northern myotis. © 2021 The Wildlife Society.

Similar hibernation physiology in bats across broad geographic ranges.

Species with broad geographic ranges may experience varied environmental conditions throughout their range leading to local adaptation. Variation among populations reflects potential adaptability or plasticity, with implications for populations impacted by disease, climate change, and other anthropogenic influences. However, behavior may counteract divergent selection among populations. We studied intraspecific variation in hibernation physiology of Myotis lucifugus (little brown myotis) and Corynorhinus townsendii (Townsend's big-eared bat), two species of bats with large geographic ranges. We studied M. lucifugus at three hibernacula which spanned a latitudinal gradient of 1500km, and C. townsendii from 6 hibernacula spread across 1200km latitude and 1200km longitude. We found no difference in torpid metabolic rate among populations of either species, nor was there a difference in the effect of ambient temperature among sites. Evaporative water loss was similar among populations of both species, with the exception of one C. townsendii pairwise site difference and one M. lucifugus site that differed from the others. We suggest the general lack of geographic variation is a consequence of behavioral microhabitat selection. As volant animals, bats can travel relatively long distances in search of preferred microclimates for hibernation. Despite dramatic macroclimate differences among populations, hibernating bats are able to find preferred microclimate conditions within their range, resulting in similar selection pressures among populations spread across wide geographic ranges.

What is winter? Modeling spatial variation in bat host traits and hibernation and their implications for overwintering energetics.

White‐nose syndrome (WNS) has decimated hibernating bat populations across eastern and central North America for over a decade. Disease severity is driven by the interaction between bat characteristics, the cold‐loving fungal agent, and the hibernation environment. While we further improve hibernation energetics models, we have yet to examine how spatial heterogeneity in host traits is linked to survival in this disease system. Here, we develop predictive spatial models of body mass for the little brown myotis (Myotis lucifugus) and reassess previous definitions of the duration of hibernation of this species. Using data from published literature, public databases, local experts, and our own fieldwork, we fit a series of generalized linear models with hypothesized abiotic drivers to create distribution‐wide predictions of prehibernation body fat and hibernation duration. Our results provide improved estimations of hibernation duration and identify a scaling relationship between body mass and body fat; this relationship allows for the first continuous estimates of prehibernation body mass and fat across the species' distribution. We used these results to inform a hibernation energetic model to create spatially varying fat use estimates for M. lucifugus. These results predict WNS mortality of M. lucifugus populations in western North America may be comparable to the substantial die‐off observed in eastern and central populations.

BATS TRANSIT AND FORAGE OVER NEARSHORE ENVIRONMENTS IN THE NORTHERN GULF OF ALASKA

We present evidence of bats transiting and foraging over the ocean along nearshore environments in the northern Gulf of Alaska. Acoustic surveys were conducted on 2 sea-based vessels that anchored overnight off the coasts of 2 national parks (July–August 2019). We documented Little Brown Myotis (Myotis lucifugus) transiting and foraging over the ocean at 14 sites within the nearshore zone at an average off-coast distance of 298 m (s = 154). Little Brown Myotis inhabiting coastal habitats in Alaska are utilizing nearshore environments similar to Vespertilionid bats in the North Atlantic.

Thomas H. Kunz

Thomas H. Kunz

Do black‐tailed prairie dog (Cynomys ludovicianus) colonies attract foraging bats?

AbstractBlack‐tailed prairie dog (BTPD) colonies are known to be hotbeds of biodiversity. Manipulation of landscape by BTPDs increases plant and animal diversity in grasslands, and thus BTPDs are considered ecosystem engineers. If BTPD colonies induce increases in insect diversity in the eastern foothills of Colorado, as shown for other areas, it stands to reason that insectivorous bats may respond by increasing their activity in those areas. I tested this hypothesis in the north‐eastern foothills habitat of Colorado, USA, by surveying for echolocation calls within four BTPD colonies and adjacent reference sites lacking BTPD burrows. Results show that bats were significantly more active in BTPD colonies than at adjacent reference sites. In addition, of the nine resident bat species, small‐footed myotis (Myotis ciliolabrum) showed the most consistent relationship with BTPD colonies. Other species that were more active in BTPD colonies included little brown myotis (M. lucifugus), fringed myotis (M. thysanodes), big brown bats (Eptesicus fuscus), and hoary bats (Lasiurus cinereus). The typically forest‐edge adapted species, M. ciliolabrum, and M. thysanodes a forest‐adapted specialist, were active more than expected in treeless BTPD colonies indicating the BTPD colonies are providing a resource not present outside colony perimeters. This study provides the first evidence of a relationship between BTPD colonies and bats in western North America.

Integrating Multiple Survey Techniques to Document a Shifting Bat Community in the Wake of White-Nose Syndrome

AbstractThe long-term study of bat communities often depends on a diverse set of sampling methodologies that are chosen based on the species or habitat management priorities of the research project. Integrating the data from a diverse set of methodologies (such as acoustic monitoring and mist net sampling) would improve our ability to characterize changes in community structure or composition over time, such as one would expect following an emergent infectious disease such as white-nose syndrome. We developed a Bayesian state-space model to integrate these disparate data into a common currency (relative abundance). We collected both acoustic monitoring and mist net capture data over an 8-y period (2006–2014) to document shifts in the bat community in central New England, USA, in response to the onset of white-nose syndrome in 2009. The integrated data model shows a significant decline in the abundance of little brown bat Myotis lucifugus, northern long-eared bat Myotis septentrionalis, and hoary bat Lasiurus cinereus, and an increase in abundance of the eastern small-footed bat Myotis leibii and the eastern red bat Lasiurus borealis. There was no evidence for a change in abundance in the big brown bat Eptesicus fuscus since the onset of white-nose syndrome. The consistency of this model with regional estimates of decline over the same time period support the validity of our relative abundance estimate. This model provides the opportunity to quantify shifts in other communities where multiple sampling methodologies were employed, and therefore provides natural resource managers with a robust tool to integrate existing sampling data to quantify changes in community composition that can inform conservation and management recommendations.

Long-Distance Movement over a Period of Days by a Female Myotis lucifugus in Newfoundland, Canada

Myotis lucifugus (Little Brown Myotis) is a regionally migrating bat, widely distributed throughout North America. Through long-term monitoring systems deployed in 2 locations in Newfoundland, Canada, we recorded the movement of an adult female of at least 375 km over a period of 4 nights. Although not the longest travel distance recorded for this species, this observation emphasizes the capabilities of Little Brown Myotis for long-distance flights, the potential connectivity among distant maternity groups, and the value of long-term monitoring programs. To fully understand the movement patterns of Little Brown Myotis, advancements in technology and greater research effort are needed.

Social networks based on frequency of roost cohabitation do not reflect association rates of Myotis lucifugus within their roosts.

Bats are a group of mammals well known for forming dynamic social groups. Studies of bat social structures are often based upon the frequency at which bats occupy the same roosts because observing bats directly is not always possible. However, it is not always clear how closely bats occupying the same roost associate with each other, obscuring whether associations result from social relationships or factors such as shared preferences for roosts. Our goal was to determine if bats cohabitating buildings were also found together inside roosts by using anti‐collision technology for PIT tags, which enables simultaneous detection of multiple tags. We PIT‐tagged 293 female little brown myotis (Myotis lucifugus) and installed antennas within two buildings used as maternity roosts in Yellowstone National Park. Antennas were positioned at roost entryways to generate cohabitation networks and along regions of attic ceilings in each building to generate intraroost networks based on proximity of bats to each other. We found that intraroost and cohabitation networks of buildings were significantly correlated, with the same bats tending to be linked in both networks, but that bats cohabitating the same building often roosted apart, leading to differing assessments of social structure. Cohabitation rates implied that bats associate with a greater number of their roost‐mates than was supported by observations within the roost. This caused social networks built upon roost cohabitation rates to be denser, smaller in diameter, and contain nodes with higher average degree centrality. These results show that roost cohabitation does not reflect preference for roost‐mates in little brown myotis, as is often inferred from similar studies, and that social network analyses based on cohabitation may provide misleading results.

Late-autumn record of Little Brown Myotis (<i>Myotis lucifugus</i>) in north-central British Columbia

Little Brown Myotis (Myotis lucifugus) inhabits north-central British Columbia (BC), but its flight activity at the onset of hibernation is not well known. On 31 October 2019, we saw three bats flying in patterns that suggested feeding, near the north shore of the Fraser River near Prince George, BC. Observations of Little Brown Myotis flying this late in the autumn have not previously been documented this far north in interior BC. We photographed the bats, and here we describe the encounter and discuss the scientific value of our observation.

Modelling the potential efficacy of treatments for white‐nose syndrome in bats

Abstract The fungal disease white‐nose syndrome (WNS) has caused mass mortality in some species of North American bats during hibernation. We use population viability models to test if a hypothetical WNS treatment or management action could facilitate the recovery of WNS‐affected little brown myotis Myotis lucifugus populations. We modelled scenarios altering three parameters: (a) WNS severity (population growth rate of WNS‐affected populations; λWNS); (b) proportion of population treated; and (c) treatment improvement in winter survival (TIWS). Our models predict that a treatment or management action that targets an entire population with a TIWS of 40% (the average TIWS in bat trials to date) will cause a population to stabilize or increase if WNS causes an annual decline of less than 70% (i.e. λWNS > 0.30). However, for severe WNS (λWNS = 0.10), the TIWS must be at least 54% to cause a population to stabilize or increase. Where only a proportion of a WNS‐affected population is treated, population stability is much harder to achieve unless the impact of WNS attenuates over time. Our models suggest that a treatment or management action only facilitates the recovery of WNS-affected populations if WNS is mild, TIWS is high, and a large proportion of the population can be treated. If a small proportion of the population is treated, it is easier to facilitate recovery if WNS severity attenuates over time. Synthesis and applications. We modelled the predicted abundance trajectory of white‐nose syndrome‐affected little brown myotis Myotis lucifugus populations in response to a hypothetical treatment or management action. Our two types of models incorporate the complete range of possible scenarios varying three parameters: (a) population growth rate of the white‐nose syndrome‐affected population, (b) the improvement in winter survival associated with the treatment or management action, and (c) the proportion of the population treated. We suggest that our models, which can be explored using online Shiny applications, should be used in the planning phase of treatment or management action programmes for white‐nose syndrome.

Rapid Biodiversity Sampling for Bat Assemblages in Northwestern Nevada

Abstract Bat (Chiroptera) assemblages in the western North America remain understudied despite their importance to ecosystem function and vulnerability to multiple anthropogenic stressors. We present the first large-scale survey that we are aware of for bat fauna in the Black Rock Plateau of northwestern Nevada in the northern Great Basin Desert. We conducted surveys using both acoustic and mist net methods, documenting 14 species across 19 sites sampled during a four-night period in August 2016. We surveyed over water sources, usually surrounded by cliff and canyon habitat, and in salt desert scrub, sagebrush, and woodland habitats, detecting multiple sensitive bat species (spotted bat Euderma maculatum, little brown bat Myotis lucifugus, canyon bat Parastrellus hesperus) in the canyon habitats of the High Rock region. We analyzed regional species diversity and present the utility of using multiple detection methods to enhance understanding of Chiroptera biodiversity at both local and regional scales. Our results demonstrate the utility of “BioBlitz” approaches in documenting local and regional diversity and provide insight into areas with species assemblages or vulnerable species. Knowledge of these sites is increasingly important for future disease surveillance and population monitoring.

Buildings provide vital habitat for little brown myotis (Myotis lucifugus) in a high‐elevation landscape

AbstractBats in North America are currently experiencing dramatic population declines due to the disease white‐nose syndrome. The long‐term viability of vulnerable species requires recognition of critical habitats, including those also occupied by humans. Our study aimed to quantify the importance of buildings to little brown myotis (Myotis lucifugus) in Yellowstone National Park, a high‐elevation landscape with relatively few human structures and abundant alternative roosting habitat. We measured roost preferences and thermoregulation in adult male and female bats roosting in buildings, trees, and rocks using temperature‐sensitive radio‐transmitters. We also studied microclimates within each roost type for comparison to roost preferences. We found reproductive females roosting in building attics on 84% of all possible days, while males roosted exclusively in rock crevices or in trees. This dichotomous roosting pattern reflected differences in roost microclimates. All roost types buffered bats from daily minimum ambient temperatures; however, buildings were more insulated from low ambient temperatures during the middle of the maternity season. Male bats roosting in rocks and trees predominantly thermoconformed to roost temperatures, while females roosting in buildings sustained higher body temperatures than males throughout the day. Pregnant and lactating females also used torpor frequently, with skin temperatures reaching <10°C, and a gestation period lasting 49–89 d. These results show that cool summer temperatures at high elevations present an energetic challenge to little brown myotis. Buildings provide critical habitat for reproductive females and likely allow for larger populations than would be possible in their absence, making these roosts a priority for long‐term conservation of this declining species.

Changes in a summer bat community in southeastern Pennsylvania

Abstract Bat population changes are poorly understood, making it difficult to establish management priorities. In 2017, a summer mist-netting survey previously conducted in 2004 at Fort Indiantown Gap was replicated to evaluate temporal changes in the local bat community. The authors hypothesized that captures of species most affected by white-nose syndrome (WNS) would decline between survey periods, and that community structure would shift. The results showed a 100% decline in captures of northern long-eared Myotis (Myotis septentrionalis) and little brown Myotis (M. lucifugus), no change in captures of eastern red bats (Lasiurus borealis), a 276% increase in captures of big brown bats (Eptesicus fuscus), and a considerable shift in community structure. These results are consistent with expected effects of WNS on Myotis populations. Increases in big brown bat populations may result from ecological release after the decline of Myotis species, or from local or large-scale habitat change over time.

Identifying occupancy model inadequacies: can residuals separately assess detection and presence?

Occupancy models are widely applied to estimate species distributions, but few methods exist for model checking. Thorough model assessments can uncover inadequacies and allow for deeper ecological insight by exploring structure in the observed data not accounted for by a model. We introduce occupancy model residual definitions that utilize the posterior distribution of the partially latent occupancy states. Residual-based assessments are valuable because they can target specific assumptions and identify ways to improve a model, such as adding spatial correlation or meaningful covariates. Our approach defines separate residuals for occupancy and detection, and we use simulation to examine whether missing structure for modeling detection probabilities can be distinguished from that for occupancy probabilities. In many scenarios, our residual diagnostics were able to separate inadequacies at the different model levels successfully, but we describe other situations when this may not be the case. Applying Moran's I residual diagnostics to assess models for silver-haired (Lasionycteris noctivagans) and little brown (Myotis lucifugus) bats only provided evidence of residual spatial correlation among detections. Targeting specific model assumptions using carefully chosen residual diagnostics is valuable for any analysis, and we remove previous barriers for occupancy analyses-lack of examples and practical advice.

Bat activity and richness in beetle-killed forests in southern British Columbia

Wildlife species exhibit changes in behavior, population dynamics, and abundance after disturbances to forests. In western North America, large swathes of dead trees have resulted from unusually large outbreaks of bark beetles (Dendroctonus spp.) over recent decades. For bats, these tree mortality events could be either negative or positive, depending on whether cavities and crevices for roosting increase in response to beetle outbreaks and how the food supply is affected. It is therefore important to determine bat presence and activity in areas with many beetle-killed trees. We examined bat species richness in the southern interior of British Columbia, Canada, in areas with light and severe beetle-kill. We identified six bat species from acoustic recorders; the federally endangered little brown myotis (Myotis lucifugus) had the most detections. Although we surveyed stand-level vegetation, we found no systematic difference between areas identified from government aerial surveys as having had high or low beetle-kill within the previous decade. Neither beetle-kill severity nor the fine-scale vegetation that we measured correlated with bat presence or activity. We conclude that bats in this region use beetle-killed forests and that the severity of beetle-killed trees is neither adversely affecting bat presence or activity, nor enabling increased use by bats of affected forest stands in comparison to activity levels found in other high elevation forests.

Population genetics revealMyotis keenii(Keen’s myotis) andMyotis evotis(long-eared myotis) to be a single species

Recognizing delineations of gene flow among groups of animals can be challenging but is necessary for conservation and management. Of particular importance is the identification of species boundaries. Several physical and genetic traits have been used with mixed success to distinguish Myotis keenii (Merriam, 1895) (Keen’s myotis) and Myotis evotis (H. Allen, 1864) (long-eared myotis), but it is unclear whether species distinction is biologically warranted. We generated 12–14 microsatellite locus genotypes for 275 long-eared Myotis representing four species — M. keenii, M. evotis, Myotis septentrionalis (Trouessart, 1897) (northern myotis), and Myotis thysanodes Miller, 1897 (fringed myotis) — from across northwestern North America and 23 Myotis lucifugus (Le Conte, 1831) (little brown myotis) as the outgroup. Population genetic analyses revealed four well-defined groups (species): M. septentrionalis, M. thysanodes, M. lucifugus, and a single group comprising M. keenii and M. evotis. We document high rates of gene flow within M. evotis/M. keenii. Cytochrome b gene (mtDNA) sequencing failed to resolve morphologically identifiable species. We highlight the importance of geographically thorough investigation of genetic connectivity (nuclear markers) when assessing taxonomic status of closely related groups. We document a morphometric cline within M. evotis/M. keenii that may in part explain earlier analyses that led to the description of the smaller bodied M. keenii (type locality: Haida Gwaii). We conclude that M. keenii does not qualify as a genetic or biological species.

Bat species distribution and habitat associations in northern Ontario, Canada

Bats are facing threats from disease, wind power development, and climate change, which are causing populations of many species to decline. The northern range limits of many temperate species are not well characterized, but the true distribution of threatened bat species is critical information for their conservation. We used passive acoustic monitoring and false-positive occupancy models to estimate the distributions of six species of bats in northern Ontario (north of ca. 50.5°N). We confirmed the presence of big brown bats (Eptesicus fuscus), hoary bats (Lasiurus cinereus), eastern red bats (Lasiurus borealis), silver-haired bats (Lasionycteris noctivagans), little brown myotis (Myotis lucifugus), northern long-eared myotis (Myotis septentrionalis), and tri-colored bats (Perimyotis subflavus) in our study area. We found that big brown bats, hoary bats, and little brown myotis likely are more widespread and common in northern Ontario than previously thought. Our models also provided evidence of associations between temperature and habitat types and bat occupancy probabilities. Our occupancy probability maps for each species support bat conservation by providing much finer-scale distribution information than previously available. These results provide a much-needed baseline for future studies of the distribution of these bat species in northern Ontario against which to measure the effects of white-nose syndrome, resource development, and climate change.