Female Northern Long-eared Bats Research Articles

Network analysis of a northern long-eared bat (Myotis septentrionalis) maternity colony in a suburban forest patch

Abstract Many bat species are highly social, forming groups of conspecifics, particularly during the maternity season. In temperate North America, these social groups are typically comprised of closely related individuals or individuals that share some common trait (i.e. reproductive state or shared hibernacula from the previous winter). In the summer, when bats use forests for day-roosts, these social groups often demonstrate nonrandom patterns of periodically associating in common roosts and disassociating using different roosts as a ‘fission–fusion society’. As cave hibernating bat species in North America continue to decline due to the impacts of White-nose Syndrome, opportunities to describe these dynamics are becoming rare. Unfortunately, these patterns often are still poorly documented, yet understanding these behaviors is critical for species-specific habitat conservation and management. In our study, we tracked female northern long-eared bats (Myotis septentrionalis) to their day-roosts in a small, suburban forest fragment in coastal New York, USA, in the summers of 2018 and 2019. We confirmed that the bats shared roost sites and, using network analyses, analyzed social dynamics and space use. In contrast to previous research on this imperiled species in large, unfragmented core forests, we found a more dense, connected roost network that concentrated around forest patch edges. Unusual for this species, primary roosts were anthropogenic structures. Our findings suggest that northern long-eared bats can utilize small forest patches and that incorporation of specific types of anthropogenic roosts might be an effective strategy for long-term conservation in more urbanized landscapes where forest management actions to enhance day-roosting conditions are impractical and the risk of stochastic loss of roosts is high.

Unique Land Cover Classification to Assess Day-Roost Habitat Selection of Northern Long-Eared Bats on the Coastal Plain of North Carolina, USA

Reproductively successful and over-wintering populations of the endangered northern long-eared bat (Myotis septentrionalis) have recently been discovered on the Coastal Plain of North Carolina. Empirical data on resource selection within the region is limited, likely hindering management of these coastal forests. Our objectives were to determine roosting home range size, selection of day-roost tree species, second- and third-order roosting habitat selection, and to quantify the overall availability of resources in the surrounding landscape. We found core and peripheral roosting home range estimates were large, yet similar to observations from other areas of contiguous forests. Prior to juvenile volancy, female northern long-eared bats appear to select red maple (Acer rubrum), water ash (Fraxinus caroliniana), and loblolly pine (Pinus taeda) as day-roosts, but then use sweetgum (Liquidambar styraciflua), swamp bay (Persea palustris), and water tupelo (Nyssa aquatica) after juvenile volancy. At the second-order spatial scale, roosting home ranges were associated with woody wetlands farther from anthropogenic development and open water. However, within the third-order scale, northern long-eared bats were associated with undeveloped woody wetlands and upland forests, areas containing shorter trees and occurring proximal to open water. Peripheral and core areas were predicted to comprise approximately 20% of the local landscape. Our results show that complex and large tracts of woody wetlands juxtaposed with upland forests in this part of the Coastal Plain may be important for northern long-eared bats locally, results largely consistent with species management efforts in eastern North America.

Northern long-eared bats roosting in a managed forest in south-central Indiana

Forest management can have mixed impacts on tree-roosting bats. Several bat species have benefitted from increased roost availability generated by certain silvicultural methods. To further investigate the impacts of forest management on bats, we conducted a study on the federally threatened northern long-eared bat (Myotis septentrionalis) in managed forests within south-central Indiana, USA. During the summers of 2012–2015, we captured and tracked 69 female bats back to 175 roosts, for which we collected roost-scale data. We compared the frequency that roosts and random points were located in (or within 10 m of) timber harvest openings and first-stage shelterwood cuts as well as their distances to these harvest types. Female northern long-eared bats roosted in a variety of roost types in a variety of tree species. However, bats tended to roost more frequently in crevices and cavities located on live sassafras (Sassafras albidum; which were often hollow) that dominated the forest mid-story and large oaks and maples in the overstory (Quercus spp., Acer spp.). While bats used roosts that were closer to harvest openings and first-stage shelterwood cuts, they did not preferentially use or avoid roosts within these sites based on their availability. However, bats did roost within both harvest openings and shelterwood cuts. Roosts used by bats in this study area are similar to those used in other landscapes, suggesting that forest management does not affect bats’ choice of roost. Our results suggest that the roosting behavior of female northern long-eared bats are not negatively impacted by forest management, at least within these south-central Indiana forests.

Roost selection by male northern long-eared bats (Myotis septentrionalis) in a managed fire-adapted forest

Wildlife conservation in multi-use landscapes requires identifying and conserving critical resources that may otherwise be destroyed or degraded by human activity. Summer day-roost sites are critical resources for bats, so conserving roost sites is a focus of many bat conservation plans. Studies quantifying day-roost characteristics typically focus on female bats due to their much stronger influence on reproductive success, but large areas of species’ ranges can be occupied predominantly by male bats due to sexual segregation. We used VHF telemetry to identify and characterize summer day-roost selection by male northern long-eared bats (Myotis septentrionalis) in a ponderosa pine (Pinus ponderosa) forest in South Dakota, USA. We tracked 18 bats to 43 tree roosts and used an information-theoretic approach to determine the relative importance of tree- and plot-level characteristics for roost site selection. Bats selected roost trees that were larger in diameter, more decayed, and under denser canopy than other trees available on the landscape. Much like studies of female northern long-eared bats have shown, protecting large-diameter snags within intact forest is important for the conservation of male northern long-eared bats. Unlike female-specific studies, however, many roosts in our study (39.5%) were located in short (≤3 m) snags. Protecting short snags may be a low-risk, high-reward strategy for conservation of resources important to male northern long-eared bats. Other tree-roosting bat species in fire-prone forests may benefit from forest management practices that promote these tree characteristics, particularly in high-elevation areas where populations largely consist of males.

Relatedness within and among northern long-eared bat (Myotis septentrionalis) colonies at a local scale

We assessed parentage within and among maternity colonies of northern long-eared bats (Myotis septentrionalis (Trouessart, 1897)) in north-central Kentucky, USA, from 2011 to 2013 to examine colony social structure, formation, and membership dynamics. We intensively sampled colonies in close and remote (>10 km) proximity before and after targeted day-roost removal. Colonies were not necessarily composed of closely related individuals, although natal philopatry was common. Adjacent colonies often contained maternally related individuals, indicating that some pups did disperse, albeit not far from their natal home range. Whereas some young had been sired by males also collected on site, most had not, as would be expected since the species mates in fall near hibernacula across a wider landscape. The number of parentages that we inferred among colonies, however, suggests that outside the maternity season, social groups may be relatively flexible and open. Analysis of microsatellite DNA data showed a low FST(0.011) and best fit to a model of one multilocus genotypic cluster across the study area. We observed high turnover in colony membership between years in all colonies, regardless of roost-removal treatment. Our results suggest that female northern long-eared bats exhibit fidelity to a general geographic area and complex, dynamic social–genetic structure.

Landscape-scale distribution of tree roosts of the northern long-eared bat in Mammoth Cave National Park, USA

ContextThe roosting habits of many temperate zone bats are well documented at microhabitat scales, but fewer studies have included multi-scale assessments of landscape patterns in bat roost site selection.ObjectivesTo identify and assess at the landscape-scale the location of spring and early season maternity roosts of female northern long-eared bats (Myotis septentrionalis) from 2015 to 2016 at Mammoth Cave National Park (MACA), Kentucky, USA.MethodsWe used mist-nets and radiotelemetry to catch and track bats to roost trees across the landscape of MACA. Data on roosting sites were evaluated using spatial point pattern analysis to examine distributional trends of roosts. A variety of spatial covariates were used to model the effect of landscape pattern, including: forest type, elevation, and proximity to hibernacula, water, and road corridors.ResultsData indicate that roost locations of female northern long-eared bats in MACA were typically situated within 2000 m of known winter hibernacula, occurring more often at higher elevations in mesic upland deciduous forests, and in close proximity to water sources and roads. We present hypotheses to account for the patterns observed in relation to landscape features and habitat resources in the Park.ConclusionsOur data indicate that a more comprehensive understanding of habitat requirements which includes empirically-based, landscape-scale patterns, and not solely considerations at stand or local levels, could lead to better informed management policies targeting conservation of maternity habitat of forest-dwelling bats, including the northern long-eared bat, a species in decline throughout much of its distribution in North America.

Weather as a proximate explanation for fission–fusion dynamics in female northern long-eared bats

Fission–fusion dynamics appear common among temperate bats where females form roost groups that change in size and composition, as females switch roosts almost daily. One hypothesis for frequent roost switching is that females move to find suitable thermal conditions as ambient conditions change. Tests of this hypothesis have, however, been conducted mostly at roosts in artificial structures where microclimate is relatively stable. The goal of our study was to determine whether roost switching and roost use by northern long-eared bats, Myotis septentrionalis, that roost in trees are related to ambient conditions. We used generalized linear fixed effects models to explore the influence of roost characteristics and changes in ambient conditions on the likelihood of roost switching. We used canonical correlation analyses to examine the relationship between ambient conditions and roost characteristics. Roost switching was indeed linked to ambient conditions together with characteristics of roosts on the previous day; the best descriptors of roost switching differed between the two geographical regions we analysed. In Nova Scotia, females were less likely to switch roosts when it rained, particularly if they were in roosts below surrounding canopy whereas they were more likely to switch roosts when they were in roosts of high decay. Females roosted in shorter trees in earlier decay classes on warm days, as well as on windy and rainy days. In Kentucky, females were more likely to switch roosts at high temperatures, particularly when they were in roosts in high decay. Females roosted in shorter, decayed trees on warm days, and in less decayed trees with small diameter on windy and rainy days. Our results suggest bats switch roosts in response to changes in ambient conditions to select suitable roosting conditions, which may explain some of the proximate factors shaping fission–fusion dynamics of bats.

Day-roost tree selection by northern long-eared bats—What do non-roost tree comparisons and one year of data really tell us?

Bat day-roost selection often is described through comparisons of day-roosts with randomly selected, and assumed unused, trees. Relatively few studies, however, look at patterns of multi-year selection or compare day-roosts used across years. We explored day-roost selection using 2 years of roost selection data for female northern long-eared bats (Myotis septentrionalis) on the Fort Knox Military Reservation, Kentucky, USA. We compared characteristics of randomly selected non-roost trees and day-roosts using a multinomial logistic model and day-roost species selection using chi-squared tests. We found that factors differentiating day-roosts from non-roosts and day-roosts between years varied. Day-roosts differed from non-roosts in the first year of data in all measured factors, but only in size and decay stage in the second year. Between years, day-roosts differed in size and canopy position, but not decay stage. Day-roost species selection was non-random and did not differ between years. Although bats used multiple trees, our results suggest that there were additional unused trees that were suitable as roosts at any time. Day-roost selection pattern descriptions will be inadequate if based only on a single year of data, and inferences of roost selection based only on comparisons of roost to non-roosts should be limited.

Distribution and Roost Selection of Bats on Newfoundland

We studied the distribution and ecology of male and female Myotis lucifugus (Little Brown Bats) and M. septentrionalis (Northern Long-eared Bats) on Newfoundland, where conditions (e.g., resource availability, abiotic conditions) were expected to be less favorable than in areas where most studies of conspecifics have occurred. We found that both species were patchily distributed and that Northern Long-eared Bats were more widely distributed across the island than previously documented. We located and characterized 36 roost trees from 14 female (6 lactating and 8 non-lactating) Northern Long-eared bats and found that, relative to conspecific populations on mainland North America, female Northern Long-eared Bats on the northern peninsula of Newfoundland roosted in shorter trees with smaller diameters. We also found that roosts used by lactating Northern Long-eared females were in cavities of large-diameter trees that maintained more stable microclimates compared to roosts used by non-lactating females.

Do social networks of female northern long-eared bats vary with reproductive period and age?

Social structure, which is a function of the patterns of interactions among individuals, is particularly variable in fission-fusion societies. The underlying factors that drive this variation are poorly understood. Female northern long-eared bats (Myotis septentrionalis) live in fission-fusion societies where females form preferred associations within groups that vary daily in size and composition as individuals switch roosts. The goal of our study was to test the predictions that preferred associations and social networks of female northern long-eared bats vary with reproductive period and age. We also tested the prediction that preferred relationships persist across years despite movements from summer roosts to winter hibernacula. Network analyses revealed that during gestation, females roosted in smaller groups where they roosted more regularly with fewer individuals than during lactation. This variation may reflect different social strategies to mediate higher energetic costs during lactation. Females of all ages roosted more often with younger individuals, which in turn had more direct and indirect associations than all other age classes. Younger individuals may play a role in maintaining connections between individuals, perhaps as a result of younger individuals being more exploratory. Temporal analyses suggested that relationships can persist for years as some pairs roosted together for multiple summers. We suggest that the dynamic nature of fission-fusion societies is associated with individual strategies to increase fitness relative to individual characteristics, in this case reproductive condition and age.

Roost selection by male and female northern long-eared bats in a pine-dominated landscape

We radiotracked 17 male northern long-eared bats ( Myotis septentrionalis) to 43-day roosts and 23 females to 49-day roosts in the Ouachita Mountains of central Arkansas during summers 2000–2005. We compared characteristics of roost trees between males and females, and compared characteristics of sites surrounding roosts with random locations for each sex. Roosts were located in cavities, crevices, and under loose bark, primarily in snags; 85% of male and 95% of female roosts were in snags. Shortleaf pine ( Pinus echinata) was the most utilized tree species (71% of roosts) and both sexes preferred ( P < 0.05) pine snags over hardwood snags. Most (80%) snag roosts were in snags 10–24.9 cm dbh, but females roosted in snags of greater diameter than males and males tended to roost more in small (<10 cm dbh) hardwoods than females. Female roost sites were more likely to have fewer large (≥25 cm dbh) hardwoods, fewer midstory pines 5–9.9 cm dbh, fewer small (<10 cm dbh) hardwood snags, more overstory pines ≥25 cm dbh, and more pine snags <10 cm dbh than random sites. Most (55%) female roosts were located in pine-dominated stands that had undergone partial harvesting and midstory removal. Males were more likely to select sites with abundant large (≥25 cm dbh) overstory pines, fewer small overstory pines (10–24.9 cm dbh), and more large pine snags ≥10 cm dbh than random. More male roosts (42%) were in unharvested stands than female roosts (24%), and females roosted at sites with fewer midstory trees than males. Our results demonstrate the importance of pine snags as roosting habitat for northern long-eared bats and the importance to females of snags located in relatively open forests in the Ouachita Mountains during summer.

Roost tree use by maternity colonies of Indiana bats and northern long-eared bats in southern Illinois

Roost trees used by female Indiana bats ( Myotis sodalis), a federally endangered species, and sympatric northern long-eared bats ( Myotis septentrionalis) at two locations in southern Illinois greatly impacted by past flooding were located using radiotelemetry. For 30 Indiana bats, we located 49 roosts in 7 species of trees. Green ash snags ( Fraxinus pennsylvanica) and pin oak snags ( Quercus palustris) were used more than expected and sweetgum snags ( Liquidambar styraciflua) less than expected based on availability. Ten adult female northern long-eared bats were tracked to 19 different trees of 5 species. We used logistic regression to predict use of roost versus random trees for both species, and to compare roosts of Indiana bats versus northern long-eared bats. Indiana bats typically roosted in areas of low vegetative obstruction (clutter) on the forest edge ( χ 2 = 10.28, d.f. = 2, P = 0.006). Compared to random trees, roosts of northern long-eared bats were within intact forests ( χ 2 = 10.56, d.f. = 1, P = 0.001). Amount of obstruction and decay differed; roosts of M. sodalis typically were less cluttered and more decayed than those of M. septentrionalis ( χ 2 = 38.63, d.f. = 2, P < 0.001). Indiana bats roosted almost exclusively under exfoliating bark of bottomland snags, whereas northern long-eared bats also made extensive use of cavities and crevices. Indiana bats cannot be expected to remain in an area indefinitely if snag creation is not sustained, and natural forest succession should be considered in long-term management of this endangered species.

INTERSPECIFIC AND INTERSEXUAL VARIATION IN ROOST-SITE SELECTION OF NORTHERN LONG-EARED AND LITTLE BROWN BATS IN THE GREATER FUNDY NATIONAL PARK ECOSYSTEM

Abstract Although only 2 bat species are common in the Greater Fundy National Park Ecosystem of New Brunswick, Canada, 4 distinct groups occur in terms of roost-site selection due to sexual segregation. We found that female northern long-eared bats (Myotis septentrionalis) roosted alone or as part of maternity colonies in mature, shade-tolerant deciduous stands. A roost site was 24 times more likely to be in a shade-tolerant deciduous tree than a coniferous tree, and trees in the mid-decay classes were 5.2 times more likely to be used than live or recently dead trees. Male northern long-eared bats roosted alone in coniferous stands or conifer-dominated mixedwood stands, and they selected roost trees that were in the mid-decay stages. Trees in mid-decay stages were selected more than twice as often as trees at the early or late stages of decay. For every 10% increase in the proportion of coniferous trees in the plot, the chances of a male northern long-eared bat roosting in the plot increased 1.5 times. Fe...