Population dynamics of little brown bats (Myotis lucifugus) at summer roosts: Apparent survival,fidelity, abundance,and the influence of winter conditions

1. White‐nose syndrome (WNS) has caused the death of millions of bats, but the impacts have been more difficult to identify in western North America. Understanding how WNS, or other threats, impacts western bats may require monitoring other roosts, such as maternity roosts and night roosts, where bats aggregate in large numbers.
2. Little brown bats (Myotis lucifugus) are experiencing some of the greatest declines from WNS. Estimating survival and understanding population dynamics can provide valuable data for assessing population declines and informing conservation efforts.
3. We conducted a 5‐year mark–recapture study of two M. lucifugus roosts in Colorado. We used the robust design model to estimate apparent survival, fidelity, and abundance to understand population dynamics, and environmental covariates to understand how summer and winter weather conditions impact adult female survival. We compared the fidelity and capture probability of M. lucifugus between colonies to understand how bats use such roosts.
4. Overwinter survival increased with the number of days with temperatures below freezing (β > 0.100, SE = 0.003) and decreased with the number of days with snow cover (β < −0.40, SE < 0.13). Adult female fidelity was higher at one maternity roost than the other. Overwinter and oversummer adult female survival was high (>0.90), and based on survival estimates and fungal‐swabbing results, we believe these populations have yet to experience WNS.
5. Recapture of M. lucifugus using antennas that continuously read passive integrated transponder tags allows rigorous estimation of bat population parameters that can elucidate trends in abundance and changes in survival. Monitoring populations at summer roosts can provide unique population ecology data that monitoring hibernacula alone may not. Because few adult males are captured at maternity colonies, and juvenile males have low fidelity, additional effort should focus on understanding male M. lucifugus population dynamics.

     

Distribution and population densities of seven species of bat in northern England

Distribution and minimum population densities for seven UK bat species known to be resident in northern England were calculated in an area covering 2500 km². The species present were pipistrelle ( Pipistrellus pipistrellus ), brown long-eared ( Plecotus auritus ), Daubenton's ( Myotis daubentonii ), whiskered ( Myotis mystacinus ), Natterer's (Myotis nattereri) , noctule ( Nyctalus noctula ) and Brandt's (Myotis brandtii). Data were collected primarily from counts at summer roosts over the period 1983 to 1990. A total of 310 bat roosts were discovered within the study area. Of the 256 roosts at which the species present was identified, the majority, 127 (49.6%) were P. pipistrellus , with a mean maternity roost size of 69.6 bats. A minimum population density of 12.6 batskm⁻² was estimated for P. pipistrellus , based on summer (maternity) roosts. The minimum population density estimate was higher than previous studies in northern England but substantially lower than those reported in Scotland (18.2 bats km-⁻²). The combined density of M. mystacinus, M. brandtii, and P. pipistrellus , which have similar foraging styles (15.8 bats km⁻²), is comparable to Scottish P. pipistrellus densities. The density of M. duubentonii was also lower than in Scotland, although the density of P. auritus was comparable. The majority of summer roosts for all species were found in buildings, except N. noctula and M. duubentonii which used bridges/tunnels or trees.     

Longevity and survival of female pipistrelle bats (Pipistrellus pipistrellus) on the Vale of York, England

Female pipistrelle bats ( Pipistrellus pipistrellus Schreber) form large nursery colonies in summer. Between 1977 and 1984, around York in the north of England, 1328 pipistrelle bats were ringed. Ninety adult females were ringed in 1977, and from capture, release and recapture data life tables for an unaged female cohort were constructed. Age-specific survival rate for adult females on the Vale of York was 0–64 per year. Three bats from the original 1977 cohort were recaptured in 1984 and are likely to have been at least eight years old. Juvenile female pipistrelles appear to survive less well than adults.     

Bats as an indicator of human activity in the paleolithic, using the example of denisova cave, northwestern Altai

Landscape and climatic changes in northwestern Altai at the end of the Middle Pleistocene were accompanied by a transformation in the taxonomic composition of the bat community and abundance of some species. The dynamics of the bat community is very important for the study of the activity of Paleolithic man. The high sensitivity of bats to human disturbance allowed the time of colonization and nature of usage of Denisova cave by humans to be recognized. In this respect, bats are a very important indicator of events in the surrounding ecosystem.     

Mitochondrial DNA (mtDNA) reveals that female Bechstein's bats live in closed societies

We present a microgeographic analysis of mitochondrial DNA (mtDNA) in Bechstein's bats using three sources of control region sequence variability, including a novel mtDNA microsatellite, to assess individual relatedness both within and among 10 maternity colonies. Comparison of marker variability among 268 adult females revealed little genetic variability within each colony. However, most colonies were clearly distinguished by colony-specific mitochondrial haplotypes (total n = 28). Low intracolony variability and strong haplotype segregation among colonies, was reflected by an extraordinary high FST of 0.68, indicating a very low intercolony dispersal rate of approximately one female in five generations. Haplotype distribution among 18 solitary males showed that males frequently disperse between colony locations, indicating the absence of dispersal barriers. Bechstein's bat maternity colonies are thus closed groups that comprise 20-40 females probably belonging to only one or, at most, two matrilines. The genetic population structure of Bechstein's bats is in agreement with the hypothesis that females seek familiar and, at least, partially related cooperation partners for raising their young. Alternatively strong philopatry might reflect the importance of profound roost or habitat knowledge for successful reproduction in female Bechstein's bats.     

Bat rabies surveillance in France: first report of unusual mortality among serotine bats

Background

Rabies is a fatal viral encephalitic disease that is caused by lyssaviruses which can affect all mammals, including human and bats. In Europe, bat rabies cases are attributed to five different lyssavirus species, the majority of rabid bats being attributed to European bat 1 lyssavirus (EBLV-1), circulating mainly in serotine bats (Eptesicus serotinus). In France, rabies in bats is under surveillance since 1989, with 77 positive cases reported between 1989 and 2016.

Case presentation

In the frame of the bat rabies surveillance, an unusual mortality of serotine bats was reported in 2009 in a village in North-East France. Six juvenile bats from an E. serotinus maternity colony counting ~200 individuals were found to be infected with EBLV-1. The active surveillance of the colony by capture sessions of bats from July to September 2009 showed a high detection rate of neutralising EBLV-1 antibodies (≈ 50%) in the colony. Moreover, one out of 111 animals tested was found to shed viable virus in saliva, while lyssavirus RNA was detected by RT-PCR for five individuals.

Conclusion

This study demonstrated that the lyssavirus infection in the serotine maternity colony was followed by a high rate of bat rabies immunity after circulation of the virus in the colony. The ratio of seropositive bats is probably indicative of an efficient virus transmission coupled to a rapid circulation of EBLV-1 in the colony.

     

Activity patterns of pipistrelle bats (Pipistrellus pipistrellus) in Oxfordshire

A maternity colony of pipistrelle bats ( Pipisfrellus pipistrellus ), in Oxfordshire, was monitored between 1 March 1989 and 6 October 1989. An infra-red 'automatic bat counter' was installed at the roost, to record the number of bats entering and leaving each minute throughout the night. Air temperature, light intensity at sunset, cloud cover, wind speed and rain were recorded on each night of monitoring. Insect abundance was estimated on 18 nights.
The nightly activity pattern was found to be unimodal in pregnancy, bimodal during lactation and unimodal post-weaning. The mean time that each bat spent outside the roost ranged from 103–483 min, with a mean of 321 min.
Ambient air temperature and length of night were significant factors affecting mean time spent outside the roost. The percentage of the night which the bats spent away from the roost ranged from 22 to 88%, with a mean of 64%. There was a significant positive correlation between ambient air temperature and percentage of the night spent away from the roost. Insect abundance showed no significant correlation with the time that bats spent outside the roost. Wind and rain had no apparent effect on time spent outside the roost.     

Anthropogenic impacts on Costa Rican bat parasitism are sex specific

While anthropogenic impacts on parasitism of wildlife are receiving growing attention, whether these impacts vary in a sex‐specific manner remains little explored. Differences between the sexes in the effect of parasites, linked to anthropogenic activity, could lead to uneven sex ratios and higher population endangerment. We sampled 1108 individual bats in 18 different sites across an agricultural mosaic landscape in southern Costa Rica to investigate the relationships between anthropogenic impacts (deforestation and reductions in host species richness) and bat fly ectoparasitism of 35 species of Neotropical bats. Although female and male bat assemblages were similar across the deforestation gradient, bat fly assemblages tracked their hosts closely only on female bats. We found that in female hosts, parasite abundance per bat decreased with increasing bat species richness, while in male hosts, parasite abundance increased. We hypothesize the differences in the parasite–disturbance relationship are due to differences in roosting behavior between the sexes. We report a sex‐specific parasite–disturbance relationship and argue that sex differences in anthropogenic impacts on wildlife parasitism could impact long‐term population health and survival.     

Day roost selection in female Bechstein's bats (Myotis bechsteinii): a field experiment to determine the influence of roost temperature

The decision where to live has far-reaching fitness consequences for animals. In contrast to most other mammals or birds that use sheltered nest sites, female Bechstein's bats frequently switch day roosts during one breeding season, and therefore must often decide where to spend the day. Selecting the right roost is important, because roost quality, e.g. microclimatic condition, influences survival and reproduction in bats. Although thermal factors are very important for the quality of roosts occupied by bats, whether bats base their day roost selection directly on roost temperature has not been tested in the field. Over one summer, we examined and tested the roost choice of 21 individually marked female Myotis bechsteinii living in one maternity colony. In a field experiment, we allowed the bats to choose between relatively warm versus cold bat boxes, while controlling for site preferences. We expected females to exhibit a preference for warm roosts during pregnancy and lactation to accelerate gestation and shorten the period of growth of their young. Roost occupancy over 160 census days reflected significant temperature differences among 89 surveyed roosts (14 tree holes and 75 bat boxes), and preferences changed with the season. Females significantly preferred cold roosts before parturition, whereas post-partum, they significantly favoured warm roosts. Temperature preferences were independent of the roost site, and thus roost selection was based directly on temperature. Boxes with significantly different daytime temperatures did not differ significantly at night. Consequently, bats would have to spend at least 1 day in a new roost to test it. Information transfer among colony members might facilitate knowledge of roost availability. Access to many roosts providing different microclimates is likely to be important for successful reproduction in the endangered Bechstein's bat.     

Occurrence of bats in northernmost Sweden (65°N) and their feeding ecology in summer

The population density of the northern bat Eptesicus nilssoni at 65° N was about one-fifth of that in southern Sweden (57° N). No other bat species was observed at 65° N. In one maternity colony, young northern bats were born in July and were flying by early August. The diet consisted mainly of small insects, predominantly dipterans, which were captured and eaten in the air. The bats maintained a nocturnal (22:00–02:30 h) foraging schedule in summer, partly reflecting the activity of insects, and spent about three hours away from the day roost each night. Owing to the short periods of darkness, the foraging flights usually started and ended in daylight. Habitat use reflected the occurrence of small insects near vegetation.     

Social interactions among wild female Bechstein's bats (<Emphasis Type="Italic">Myotis bechsteinii</Emphasis>) living in a maternity colony

Although sociality is common in bats, few studies have investigated individual social behaviour in free-ranging colonies. This study quantifies social interactions among wild female Bechstein's bats (Myotis bechsteinii) belonging to one maternity colony. Our main goal was to analyse allogrooming and nose rubbing, which are both regularly displayed by adult females. Based on data of individually marked bats with known degrees of pairwise relatedness, we suggest that allogrooming has both a social and a hygienic function. Females groomed colony mates mainly on parts of the body that are difficult to reach by a bat itself. Thus, allogrooming may function to remove ectoparasites from inaccessible body parts. Allogrooming was rare compared to self-grooming (on average 0.7% vs 37.7% of a female's total observation time), and there was no significant correlation between the rate at which a bat groomed itself and the frequency with which it was groomed by conspecifics. Therefore, we assume that allogrooming also has a social purpose in addition to its assumed hygienic function. We suggest that allogrooming could strengthen social bonds among colony members that live together for many years. Mothers and adult daughters groomed each other preferentially. Thus, allogrooming may reflect special mother–daughter bonds. Nose rubbing occurred mainly within minutes (median: 80 s) after the arrival of a female in a night roost, and there was no correlation with relatedness. Therefore, it probably allows recognition of colony mates and may also be a greeting behaviour. Communicated by M.E. dos Santos     

Spatial Proximity between Newborns Influences the Development of Social Relationships in Bats

Although bats are highly social mammals, the mechanisms influencing the establishment of social structures are far from being fully understood. So far, no study has addressed the effects of spatial proximity between newborns such as that occurring in nursery clusters on the development of preferential associations among individuals. We tested such effects on captive pups of Kuhl’s pipistrelle Pipistrellus kuhlii. During the first 6 wks, we kept them in separate rearing groups. Once able to fly, bats were allowed to freely interact in a common flight room, where those reared in the same groups showed higher rates of amicable interactions (proximity during roosting, allogrooming, huddling) but no effect on aggressive behaviour. Sex also influenced such frequencies, females being more likely to interact amicably. The phenomenon we describe may have significant implications for the development of bat social structures, including colony aggregation, within‐colony cryptic subunits or preferred association of individuals in fission–fusion dynamics. Our study adds a further dimension to bat sociality, highlighting the implications of spatial proximity in an early age phase.     

Indiana bat summer maternity distribution: effects of current and future climates

Temperate zone bats may be more sensitive to climate change than other groups of mammals because many aspects of their ecology are closely linked to temperature. However, few studies have tried to predict the responses of bats to climate change. The Indiana bat (Myotis sodalis) is a federally listed endangered species that is found in the eastern United States. The northerly distribution of Indiana bat summer maternity colonies relative to their winter distributions suggests that warmer climates may result in a shift in their summer distribution. Our objectives were to determine the climatic factors associated with Indiana bat maternity range and forecast changes in the amount and distribution of the range under future climates. We used Maxent to model the suitable climatic habitat of Indiana bats under current conditions and four future climate forecasts for 2021–30, 2031–40, 2041–50, and 2051–60. Average maximum temperature across the maternity season (May–August) was the most important variable in the model of current distribution of Indiana bat maternity colonies with suitability decreasing considerably above 28ºC. The areal extent of the summer maternity distribution of Indiana bats was forecasted to decline and be concentrated in the northeastern United States and Appalachian Mountains; the western part of the current maternity range (Missouri, Iowa, Illinois, Kentucky, Indiana, and Ohio) was forecasted to become climatically unsuitable under most future climates. Our models suggest that high temperatures may be a factor in roost‐site selection at the regional scale and in the future, may also be an important variable at the microhabitat scale. When behavioral changes fail to mitigate the effects of high temperature, range shifts are likely to occur. Thus, habitat management for Indiana bat maternity colonies in the northeastern United States and Appalachian Mountains of the Southeast is critical as these areas will most likely serve as climatic refugia.     

Estimating density of a forest-dwelling bat: a predictive model for Rafinesque’s big-eared bat

Data on species distribution and abundance are the foundation of population ecology. However, due to difficulties in surveying bats, abundance estimates for tree-roosting microchiropterans are non-existent. Therefore, our objective was to develop methods for estimating colony abundance and density, taking as our model Rafinesque’s big-eared bat Corynorhinus rafinesquii, a species of conservation concern found in cypress-gum swamps of the southeastern United States. We searched 123 transects at eight study sites in the Coastal Plain of Georgia, USA to locate and characterize diurnal summer roosts of C. rafinesquii. We modeled the relationship between the number of bat colonies and landscape-scale habitat variables with zero-inflated negative binomial regression and used Akaike’s information criterion to select the most parsimonious models. We generated a predictive density map to identify areas of high colony density and to estimate overall abundance. Colony density was predicted by the duration of wetland flooding, wetland width, and study site. Application of the regression model to a GIS indicated there were 3,734 colonies containing 6,910 adult bats on the eight study sites. Predicted density ranged from 0.07 colonies/ha and 0.07 adult bats/ha in saturated wetlands to 0.47 colonies/ha and 1.18 adult bats/ha in semi-permanently flooded wetlands. This study is the first to estimate density and abundance of forest-dwelling microchiropterans over a large area. Such data can serve as a baseline for future work on population trends in C. rafinesquii. In addition, our approach could be replicated for other bat species with moderately cryptic roosts.     

Which temporal resolution to consider when investigating the impact of climatic data on population dynamics? The case of the lesser horseshoe bat (<Emphasis Type="Italic">Rhinolophus hipposideros</Emphasis>)

Climatic variables are often considered when studying environmental impacts on population dynamics of terrestrial species. However, the temporal resolution considered varies depending on studies, even among studies of the same taxa. Most studies interested in climatic impacts on populations tend to average climatic data across timeframes covering life cycle periods of the organism in question or longer, even though most climatic databases provide at least a monthly resolution. We explored the impact of climatic variables on lesser horseshoe bat (Rhinolophus hipposideros) demography based on count data collected at 94 maternity colonies from 2000 to 2014 in Britanny, France. Meteorological data were considered using different time resolutions (month, life cycle period and year) to investigate their adequacy. Model averaging was used to detect significant predictors for each temporal resolution. Our results show that the finest temporal resolution, e.g. month, was more informative than coarser ones. Precipitation predictors were particularly decisive, with a negative impact on colony sizes when rainfall occurred in October, and a positive impact for June precipitations. Fecundity was influenced by April weather. This highlights the strong impact of climatic conditions during crucial but short time periods on the population dynamics of bats. We demonstrate the importance of choosing an appropriate time resolution and suggest that analogous studies should consider fine-scale temporal resolution (e.g. month) to better grasp the relationship between population dynamics and climatic conditions.     

Roosting and Foraging Social Structure of the Endangered Indiana Bat (Myotis sodalis)

Social dynamics are an important but poorly understood aspect of bat ecology. Herein we use a combination of graph theoretic and spatial approaches to describe the roost and social network characteristics and foraging associations of an Indiana bat (Myotis sodalis) maternity colony in an agricultural landscape in Ohio, USA. We tracked 46 bats to 50 roosts (423 total relocations) and collected 2,306 foraging locations for 40 bats during the summers of 2009 and 2010. We found the colony roosting network was highly centralized in both years and that roost and social networks differed significantly from random networks. Roost and social network structure also differed substantially between years. Social network structure appeared to be unrelated to segregation of roosts between age classes. For bats whose individual foraging ranges were calculated, many shared foraging space with at least one other bat. Compared across all possible bat dyads, 47% and 43% of the dyads showed more than expected overlap of foraging areas in 2009 and 2010 respectively. Colony roosting area differed between years, but the roosting area centroid shifted only 332 m. In contrast, whole colony foraging area use was similar between years. Random roost removal simulations suggest that Indiana bat colonies may be robust to loss of a limited number of roosts but may respond differently from year to year. Our study emphasizes the utility of graphic theoretic and spatial approaches for examining the sociality and roosting behavior of bats. Detailed knowledge of the relationships between social and spatial aspects of bat ecology could greatly increase conservation effectiveness by allowing more structured approaches to roost and habitat retention for tree-roosting, socially-aggregating bat species.     

The role of olfactory cues in mother–pup,groupmate, and sex recognition of lesser flat‐headed bats,Tylonycteris pachypus

Tylonycteris pachypus is a gregarious bat species with tens of individuals in a colony. The mechanisms by which mother bats recognize their pups and adult bats recognize each other are not clear. We hypothesized that such recognition is achieved by chemical discrimination and performed experiments to test the hypothesis. Results showed that mother bats were much more attracted to the scent from their own pups. For adult bats, females were attracted to the scent from both male and female groupmates but had a higher preference to the scent from female than from male groupmates. Male bats were much more attracted to the scent from male groupmates while showed no preference to the scent from female groupmates. Within a group, both female and male bats had no difference in preference to the scent from the same or opposite sex. These results suggest that mother–pup and groupmate recognition of T. pachypus can be achieved by olfactory cues.     

Urban Maternity-Roost Selection by Big Brown Bats in Colorado

Abstract: Despite prevalent use of anthropogenic structures by bats and the associated implications for public health, management, and bat conservation, very little quantitative information exists about urban roost characteristics and their selection by bats. During the summers of 2001 to 2004 we conducted fieldwork in Fort Collins, Colorado, USA, situated on the northern end of Colorado's Front Range, to address questions of roost selection by the big brown bat (Eptesicus fuscus). The city has experienced its greatest growth in the past half century, with its population increasing by 30% in the last decade. Similar growth in new buildings has occurred, with the number of new housing permits issued annually doubling in the past decade. We located 142 roosts using radiotelemetry or by citizen calls in response to a newspaper article and flyers. To determine characteristics of roost selectivity by bats, we compared variables for known maternity roosts and randomly selected buildings at microhabitat and landscape scales using logistic regression; we used an information theoretic approach to determine which variables were most important. We considered 44 and 100 buildings in the microhabitat and landscape scale analyses, respectively. At the microhabitat scale maternity roosts had exit points with larger areas that were higher from the ground and had warmer average temperatures than randomly selected buildings. At the landscape scale distances to similarly categorized roosts were smaller, and urbanization variables such as lower building density, higher street density, and lower traffic count density were most important. Results for variables important to urban-roosting big brown bats were often analogous to studies that characterized maternity roosts found in tree snags and rock crevices. In addition, changes in the landscape, not only in the form of anthropogenic structures but also in water availability and vegetation structure such as riparian forests, may have led to population increases and range expansions of the big brown bat. Because big brown bats appear to selectively choose specific combinations of characteristics found at maternity roosts, not all available structures can be considered suitable and exclusion from established maternity roosts may negatively impact bat populations.     

Sexual differences in survival rates of adult pipistrelle bats (Pipistrellus pipistrellus) in South Sweden

Summary A pipistrelle bat (Pipistrellus pipistrellus) population in southernmost Sweden was studied for eight consecutive breeding seasons by means of bat boxes. Survival rates were calculated using Cormack's stochastic technique. The mean survival rate of adult females exceeded that of territorial males. Annual variations in survival rates were most evident in males, low rates being observed in years following wet autumns. Energy constraints imposed on territorial males by the mating system, a resource defence polygyny, were assumed to account for the differences obtained in survival rates between the sexes.     

Numerical and Functional Responses of Forest Bats to a Major Insect Pest in Pine Plantations

Global change is expected to modify the frequency and magnitude of defoliating insect outbreaks in forest ecosystems. Bats are increasingly acknowledged as effective biocontrol agents for pest insect populations. However, a better understanding is required of whether and how bat communities contribute to the resilience of forests to man- and climate-driven biotic disturbances. We studied the responses of forest insectivorous bats to a major pine defoliator, the pine processionary moth pityocampa, which is currently expanding its range in response to global warming. We used pheromone traps and ultrasound bat recorders to estimate the abundance and activity of moths and predatory bats along the edge of infested pine stands. We used synthetic pheromone to evaluate the effects of experimentally increased moth availability on bat foraging activity. We also evaluated the top-down regulation of moth population by estimating T. pityocampa larval colonies abundance on the same edges the following winter. We observed a close spatio-temporal matching between emergent moths and foraging bats, with bat activity significantly increasing with moth abundance. The foraging activity of some bat species was significantly higher near pheromone lures, i.e. in areas of expected increased prey availability. Furthermore moth reproductive success significantly decreased with increasing bat activity during the flight period of adult moths. These findings suggest that bats, at least in condition of low prey density, exhibit numerical and functional responses to a specific and abundant prey, which may ultimately result in an effective top-down regulation of the population of the prey. These observations are consistent with bats being useful agents for the biocontrol of insect pest populations in plantation forests.