Bat Boxes Research Articles

Bat box monitoring: comparing multiple contemporary methods

ABSTRACT Bat boxes can be employed to provide mitigation for the loss of trees with bat roost potential. Eighty bat boxes were deployed by the Hamilton City Council as part of the bat mitigation strategy for the Southern Links Project in southern Hamilton. Several contemporary methods were employed to determine bat box occupancy to ensure effective monitoring. This included visual scoring assessments (e.g. staining, wetness), endoscope surveys, thermal imaging, and eDNA. Emergence survey data were provided by the University of Waikato which provided further insight into the accuracy of the methods. Jointly the methods confirmed the use of 34 Kent style boxes (n = 70; 49%). Indicating a high success rate of box utilisation over a relatively short period (two years). Of the methods, eDNA confirmed the largest percentage of bat box use. Comparatively, thermal imaging provided an alternative and less intrusive means of surveying on-the-day bat presence. However, there were instances where survey conditions (e.g. terrain, vegetation clutter, solar irradiance, rainfall) influenced the reliability of thermal imaging. While visual assessment and thermal imaging cannot be solely relied on, they provide a supportive tool for other monitoring techniques. They can help guide the application of more definitive methods such as eDNA.

Caught in the web: Exploring spider predation on bats in Europe.

The intricate interplay between predators and prey has long fascinated ecologists, with bats and their diverse prey offering insight into co-evolutionary dynamics. While bats have evolved sophisticated strategies for prey capture, they also face predation pressure. Among their predators, spiders stand out for their diversity of predatory tactics, ranging from hunting assaults and web ensnarement to the deployment of venom. Yet, bat predation records by spiders are mostly from tropical regions, and cases remain notably scarce in temperate regions. Here, we report four new incidences of bat predation and mortality by spiders and their webs in Europe. Our observations include detailed photograph and video documentation of the first record of a spider capturing and consuming a bat pup in Spain, as well as accounts of bats entangled in spider webs on a building and inside bat boxes in the United Kingdom. These findings shed light on understudied predator-prey dynamics, offering valuable insights into spider predation on bats in European ecosystems. Our study emphasises the importance of continued research to improve our understanding of ecological interactions between these elusive and primarily nocturnal taxa.

Bat droppings collection by ants in epigean environments

Abstract Ants can be found in insect communities associated with droppings, but most studies about this interaction have been carried out in subterranean environments, specifically in the study of the interaction between ants and bat guano. In this report, we describe the first case of interaction between seven different ant species and the droppings of two bat species in epigean environments. The study was performed in bat roosts monitored from March to October 2022 in the Doñana Biological Reserve of the Doñana National Park (Huelva, SW Spain). It was carried out via direct observations of droppings deposited on the ground surface or in tree‐mounted dropping collectors below bat boxes. We report a total of 37 interactions by seven different species of ants with droppings of two species of bat, the soprano pipistrelle (Pipistrellus pygmaeus) and the greater noctule (Nyctalus lasiopterus), in four different habitats (Eucalyptus camaldulensis, Pinus pinea, Populus alba and ground surface). The generalist characters and the omnivorous diets of the ant species observed, in addition to the abundant availability of droppings during a period of food scarcity, suggest that droppings are transported as a food resource, with the consequent implications that this interaction may have on faecal degradation and nutrient cycling, as one of the supporting services provided by ants.

Improving the science and practice of using artificial roosts for bats.

Worldwide, artificial bat roosts (e.g., bat boxes, bark mimics, bat condos) are routinely deployed for conservation, mitigation, and community engagement. However, scant attention has been paid to developing best practices for the use of artificial roosts as conservation tools. Although bats readily occupy artificial roosts, occupancy and abundance data are misleading indicators of habitat quality. Lacking information on bat behavior, health, and fitness in artificial roosts, their conservation efficacy cannot be adequately validated. We considered the proximal and ultimate factors, such as evolutionarily reliable cues, that may prompt bats to preferentially use and show fidelity to suboptimal artificial roosts even when high-quality alternatives are available. Possible negative health and fitness consequences for artificial roost inhabitants include exposure to unstable and extreme microclimates in poorly designed roosts, and vulnerability to larger numbers of ectoparasites in longer lasting artificial roosts that house larger bat colonies than in natural roosts. Bats using artificial roosts may have lower survival rates if predators have easy access to roosts placed in conspicuous locations. Bats may be lured into occupying low-quality habitats if attractive artificial roosts are deployed on polluted urban and agricultural landscapes. To advance the science behind artificial bat roosts, we present testable research hypotheses and suggestions to improve the quality of artificial roosts for bats and decrease risks to occupants. Because continued loss of natural roosts may increase reliance on alternatives, such as artificial roosts, it is imperative that this conservation practice be improved.

Bat boxes in urban bushland are associated with inflated activity of an urban generalist bat, but not an altered community

AbstractBat boxes are often installed as substitute habitats to offset the loss of large, hollow‐bearing trees. However, emerging evidence suggests that they are failing to achieve intended conservation outcomes as they only support generalist species. Despite these concerns, the effect of bat boxes on the dynamics of bat communities remains understudied. We assessed the bat community in reserves where bat boxes had been installed in comparison with reserves where they had not using ultrasonic surveys in 16 small bushland reserves throughout Sydney, Australia. Reserves containing bat boxes and those without had comparable species diversity and composition; however, the activity of the dominant species, Gould's wattled bat (Chalinolobus gouldii), was significantly higher at sites with bat boxes. Species that commonly forage in open vegetation, including C. gouldii, were significantly positively associated with sites that had bat boxes. Occupation of boxes by bats was not recorded in the study due to limited information on their locations, so further research is required to understand the direct effects of boxes and the bats that occupy them on the bat community. If bat boxes continue to be recommended as a biodiversity offset, a greater understanding of the potential impact they have on altered competitive relationships and community dynamics is essential.

Factors affecting bat occupancy of boxes in managed coniferous forests

The gradual conversion of forest stands to single-aged and single-species stands is resulting in the loss of natural roosts for many animal groups. The installation of bat boxes is one solution to compensate for the lack of natural roosting opportunities. The box models differ in their design and material, which to some extent can determine their suitability for bats. We investigated the occupancy of 187 boxes made of wood, ceramic and two sizes concrete with styrofoam; and the intra-seasonal (spring migration, breeding, mating/migration) thermal profile for each type of box. The environment of the boxes was defined by parameters that could directly affect the box’s thermal conditions (solar energy availability), or be related to sociality (distances, obstacles) or food availability (edge of forest, water). The box occupancy depended on the box type and the season: styrofoam-concrete boxes were preferred, with a higher occupancy during the mating and migration period (>75%), whereas the highest species richness occurred in ceramic boxes. Box types also differed significantly in their diurnal thermal profiles: the wooden boxes had inside temperatures similar to outside the box, whereas the styrofoam-concrete and with expanded clay aggregate (ceramic type) averaged 2°C higher. Overall, we found 6 bat species, although we concentrated our analysis on the most common species: Pipistrellus nathusii (88%). For this species, none of the parameters that could affect the box thermal condition had an impact on the occupancy, whereas the presence of obstacles and the distance to a water body, proved to be important. To ascertain that our results may be valid and be the result of differences in the box thermal properties, we tested the relationship of the box occupancy to the latitude, using data available in the literature. The occupancy of wooden boxes from the latter dataset significantly decreases with latitude, whereas for the concrete (with addition of sawdust or styrofoam) it increases, although this relationship is not significant and requires a larger sample.

Polyrhachis femorata (Hymenoptera: Formicidae) habitat and colony defensive immobility strategy

Many animal species ‘play dead’ or feign death (in some cases called tonic immobility) as a defence strategy against predators, including some ants, although triggers and durations are poorly understood. We repeatedly observed such death-feigning behaviour in Polyrhachis femorata ants that occupied pygmy-possum nest boxes deployed on Kangaroo Island following the 2019–2020 bushfires that burnt half of the island. Most of the 759 bat and pygmy-possum boxes (901 cavities) were on burnt ground. In 3312 box cavity checks on 13 diverse properties during monitoring visits, 28 of 40 P. femorata records (first for South Australia) occurred in unburnt Critically Endangered Narrow-Leaf Mallee Woodland community, seven in adjacent mallee community containing narrow-leaf mallee, three in cup gum unburnt habitat, and two in one box on burnt ground. Fire may have affected the abundance and re-establishment of the species. Polyrhachis femorata engages in a surprising defensive immobility strategy in boxes, since it is not only undertaken by individuals facing a potential predator, but also by entire colonies. The death-feigning behaviours were complemented by plugging box entrances. Nest boxes may be used to study this mysterious behaviour in this poorly known species, although frequent observation could lead to nest abandonment by the ant.

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.

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.

Home is where the heat is: Thermoregulation of European bats inhabiting artificial roosts and the threat of heat waves

Abstract Anthropogenic land use changes, such as deforestation and commercial forestry, have substantially reduced natural roost sites for European bats. A common conservation solution is to provide artificial roosts (i.e. bat boxes), but there are concerns that these can become hotter than natural roosts in summer and could be death traps during heat waves. Nevertheless, females of several bat species form maternity colonies in these boxes, thus occupying hotter and more humid microclimates than solitarily roosting males. We tested if cooling efficiency and heat tolerance differ between sexes in European bats, and estimated the evaporative water requirements for bats living in bat boxes during hot summer days. We used indirect calorimetry and thermometry to quantify thermoregulation at high air temperatures (Ta) in four species of verspitilionid bats that regularly occupy artificial roosts. We measured resting metabolic heat production, evaporative water loss rates (EWL) and body temperature (Tb) at Ta between 28°C and 48°C during summer. We predicted that females have higher evaporative cooling efficiency (evaporative heat loss/metabolic heat production) than males, allowing them to reach their heat tolerance limit at higher Ta. We found no sex differences in maximum evaporative cooling efficiency, maximum Tb, and maximum Ta tolerated. However, the patterns of increasing EWL with Ta differed between sexes. Females tolerated higher Ta before increasing EWL than males and then rapidly increased EWL to higher values than males at the maximum Ta tolerated. These sex differences in heat dissipation strategies may reflect varying ecological and physiological constraints associated with different summer roosting habits. Synthesis and applications. Our study revealed that some small European bat species are already at risk of succumbing to lethal dehydration during present‐day heat waves, with daytime evaporative water requirements equivalent to ~30% of body mass in sun‐exposed boxes. For conservation managers working with common European bat species, particularly those in monoculture forests with woodcrete bat‐boxes, our physiologically informed recommendations include positioning boxes in diverse locations varying in aspect and sun exposure. This will ensure thermal heterogeneity of roost sites and provide a wide gradient of microclimate conditions, allowing for roost switching when necessary.

Spring showers put a dampener on reproduction success

Bat mothers invest incredible amounts of energy in raising a pup. Typically, bats mate in the autumn and hibernate over winter; however, the females do not become pregnant until the following spring and give birth in the summer. To sustain pregnancy, bats feed on insects, such as midges and flies that can become rarer when poor weather sweeps in. In addition, younger bats need to hone their insect-catching skills which can also impair their ability to raise pups. Bianca Stapelfeldt from the University of Greifswald, and colleagues from the Bat Research Project, Germany and the Nossentiner/Schwinzer Nature Park, Germany, set out to determine how weather affects the reproductive success of adult female Natterer's bats (Myotis nattereri) of different ages.Beginning in 1990 and continuing every year since, researchers have collected Natterer's bats from bat and bird boxes in the Nossentiner/Schwinzer Nature Park in Mecklenburg-Pomerania, Germany, between July and September. The researchers measured the body mass, forearm length (measurement of body size) and identified the bat's age (whether they were adult or juvenile), before marking the bats with forearm bands to keep track of individuals through the years. In addition, the scientists noted whether the adult females had given birth that year by assessing the fur around the nipple; if there was fur, then the bat likely did not have a pup, while a lack of fur meant that she had given birth to a pup that season. Over the decades, the team also monitored archived climate data from a nearby meteorological station in Goldberg, Germany, and identified the average and lowest temperatures, the daily precipitation levels and the overnight wind speeds and total precipitation levels from 2003 to 2020.The team found that over the 17-year period, the younger adult female bats had less success in birthing and rearing baby bats, compared with older adult females, likely because the younger mothers may be unable to provide themselves with the immense amount of energy required during pregnancy and when feeding their pups. The researchers speculate that younger adult bats may forgo pregnancy to avoid investing energy into a pup that they may be unable to raise. Interestingly, wetter springs also resulted in lower birth rates in younger adult bats, which was not seen with the older mothers. The researchers suspect that rainy periods make it difficult for the bats to echolocate and hunt for food and to stay warm. Therefore, poor weather may cause the bats’ body weight to reach a critical low, so that younger bats may forgo pregnancy altogether.In addition, the researchers identified a 2-week window (from the end of April to 11 May) where poor weather had the greatest negative impact on the females’ pregnancies. It is unknown when Natterer's bats become pregnant, but this 2-week critical period is the same time pregnancies begin for other bats across Europe. Since pups have little time to grow and prepare for hibernation, adult females cannot delay their pregnancies any later, and so may abandon pregnancies if they experience adverse weather during this pivotal period.Stapelfeldt and colleagues have successfully shown the impact of poor weather on the pregnancy and baby rearing by bat mothers using long-term monitoring of a bat population and the weather conditions they encounter. Climate change is an imminent threat worldwide and many European countries are likely to become increasingly wet during this critical period for bat pregnancies, which could dramatically affect the ability of bat populations to reproduce. Increases in rainfall during the spring may be a particular threat for European bat species at risk of extinction.

Evaluating bat boxes: design and placement alter bioenergetic costs and overheating risk

Bat box microclimates vary spatially and temporally in temperature suitability. This heterogeneity subjects roosting bats to a variety of thermoregulatory challenges (e.g. heat and cold stress). Understanding how different bat box designs, landscape placements, weather and bat use affect temperature suitability and energy expenditure is critical to promote safe and beneficial artificial roosting habitat for species of conservation concern. From April to September 2019, we systematically deployed 480 temperature dataloggers among 40 rocket box style bat boxes of 5 designs and regularly monitored bat abundance. We used bioenergetic models to assess energy costs for endothermic and heterothermic bats and modelled the overheating risk for each box as a function of design, placement, bat abundance and weather. For endothermic bats, predicted daily energy expenditure was lower for solar-exposed placements, large group sizes and a box design with enhanced thermal mass. For heterothermic bats, shaded landscape placements were the most energetically beneficial and bat box design was not important, because all designs generally offered microclimates suitable for torpor use at some position within the box. Overheating risk was highest for solar-exposed landscape placements and for designs lacking modifications to buffer temperature, and with increasing bat abundance, increasing ambient temperature and slower wind speeds. The external water jacket design, with the greatest thermal mass, concomitantly decreased overheating risk and endothermic energy expenditure. By assessing bat box suitability from two physiological perspectives, we provide a robust method to assess the conservation value of bat box design and placement strategies. We recommend future studies examine how changing thermal mass and conductance can be used to diminish overheating risk while also enhancing the effects of social thermoregulation for bat box users.

What makes a good bat box? How box occupancy depends on box characteristics and landscape‐level variables

Abstract Bat populations are in steep decline and presently, 16% of all species are classified as ‘threatened’. One main driver identified for this decline is the loss of natural roosting opportunities, caused by the removal of natural habitats. Installation of bat boxes is one solution to compensate for the lack of natural roosting opportunities. Current recommendations for box design emphasize low maintenance costs and are rarely based on empirical evidence. We investigated occupancy of 13,634 bat boxes in northern Bavaria, Germany. In our study, boxes differed in type, age and mounting height, as well as in maximum community age, that is the length of time a group of boxes had been installed in a particular place, the size of box groups and the distance to the next box in the surrounding area, that is box isolation. Our results showed that box occupancy depended on box type and bat species. As a case study, we analysed the two most common species found within the investigated boxes, Pipistrellus pipistrellus and Myotis nattereri, in more detail. Both species showed preference to a voluminous box that had a narrow entrance (‘Gable box’ 14 mm). For P. pipistrellus, only box type affected occupancy, whereas for M. nattereri, the relationship between box type and box age was important. Older boxes and boxes in areas with higher maximum community age of boxes showed higher box occupancy by bats. Box occupancy decreased with the distance between adjacent box groups (‘box isolation’). High mounting height showed a tendency for increased box occupancy, but the effect was only weakly significant. Because of the species‐specific responses in our study, we suggest installing a combination of different box types, including at least one box type with a narrow entrance (14 mm). Boxes should be placed as box groups of three to four boxes, and there should be short distances between adjacent box groups. We also recommend installing new box groups close to areas of high maximum community age of boxes.

Methods for assessing artificial thermal refuges: Spatiotemporal analysis more informative than averages

1Thermal refuges are widely used by animals of all taxonomic groups and are critical to survival in severe weather. 2Human activities are reducing the availability of natural refuges; consequently, artificial refuges are used as conservation management tools, particularly for bats. 3Published box evaluations are generally incomplete, omitting thermal physiology and relevant thermal properties. 4Here, we compare methods for evaluating the potential utility of bat box designs for bats and present a graphical spatiotemporal method that provides more complete information. 5For illustration, we compare the original to three modified versions of the “rocket box” style bat box. 6Box internal temperatures and generalized thermal physiology models are combined in two suitability indices appropriate to the mother, and to pups. 7Results revealed that daily and seasonal averages of these indices obscured important processes and showed insignificant differences among bat box design modifications. 8In contrast, graphical analysis highlighted the presence and spatiotemporal structure of significant differences among boxes, which were most evident in sunny weather. 9Differences among boxes were sensitive to assumptions about bat thermal physiology and behavior. 10We found that an external water jacket mitigated temperature extremes and extended favorable temperatures into the night, which could enhance pup development while the mothers foraged. 11Further experiments are needed to evaluate the relation between metabolic heating by box occupants and thermal conditions within bat boxes.

Avoiding a conservation pitfall: Considering the risks of unsuitably hot bat boxes: Adding context to Crawford & O'Keefe

AbstractAs practitioners of mitigation and conservation of bats, we think use of artificial bat roosts contribute to bat conservation and should be encouraged. Problems with boxes identified by Reed and O'Keefe also exist with natural roosts, and they are more readily studied and managed with artificial than natural roosts. Use of boxes also provides an opportunity for citizen science, but more importantly engenders citizen conservation.

Design modifications affect bat box temperatures and suitability as maternity habitat

Abstract Artificial roosting structures (e.g. bat boxes) are widely used as conservation tools for many animals, including bats. Although it is relatively easy to monitor bat box temperatures, we know little about the effect of design on temperatures within a box. Box microclimate affects energy budgets and physiological processes and, thus, suitability as a roost. Optimal temperature varies during the period when reproductive females aggregate to rear pups; warm roosts enhance pup development during gestation and lactation, while cool roosts facilitate energy savings by torpor, which is often important during post‐lactation. To better understand the relation of design to internal temperature, we simultaneously compared 20 box designs (19 variations of a rocket box and one three‐chamber flat box) in an open site, May to September 2018. We measured temperatures at the top, middle and bottom of each box and tallied counts of daytime and nighttime cool (≤30°C; TCOOL), permissive (30.1–39.9°C; TPERM) and stressful (≥40°C; TSTRS) temperature observations. We also measured temperature, solar radiation and wind speed at the site. We used generalized linear models with negative binomial distributions to test the effects of design, environmental variables and their interactions. Adding an external jacket or decreasing ventilation increased daytime and nighttime counts of TPERM. Increasing box volume (i.e. lengthening box by 50%) also positively affected daytime counts of TPERM, whereas decreasing box volume (by 50%) had the opposite effect. Adding an external water jacket was the only modification we tested that decreased counts of TCOOL at night. Counts of TSTRS were elevated by warmer, sunnier and less windy conditions outside, but these effects were lessened by increasing roof shading or reflectivity, adding ventilation or external jackets, or decreasing box volume. These results inform the development and implementation of novel bat box designs as conservation and management tools for maternal colonies of bats, with consideration for the effects of weather on internal temperatures.

Are Echo-Reflective Cues Effective to Attract Bats to Newly Placed Artificial Roosts?

The availability of suitable roosts is an important factor affecting the viability of bat populations. In Europe and North-America, the installation of artificial roosts is a standard conservation measure to mitigate the loss of tree cavities or crevices at buildings. How quickly artificial roosts, such as bat boxes, are adopted, depends on how easily the bats can find them, and on their suitability for roosting. While there is some information about how the design of bat boxes influences their occupancy, it is unknown to what extent the use of bat boxes depends on their detectability. In this experimental field study, we studied the roost selection behavior of three forest-living bat species. We investigated whether attaching an external echo-reflector to bat boxes influenced the time until the bats discover a box or the total number of discovered boxes, which are proxies for detectability. We also assessed whether this modification improved the occupancy of newly placed boxes, as a proxy for their attractiveness. As a result of a previous study, all studied bat colonies were familiar with the echo-reflector as an indicator for the suitability of bat boxes as a day roost. For each species, we compared between boxes with and without an echo-reflector, the number of boxes discovered, the number of days elapsed until discovery, the number of subsequent visits, and the number of days that each box type was used as day roosts. Myotis bechsteinii and Myotis nattereri discovered, visited and used more unmodified boxes than boxes with echo-reflectors. Plecotus auritus did not show differences in behavior with regard to the box types. Our results show that attaching an echo-reflector to newly placed artificial roosts does not improve their discovery and subsequent occupation, even when bats are already familiar with this cue as an indicator of suitability. We discuss the implication of our findings for bat conservation.

Using mounting, orientation, and design to improve bat box thermodynamics in a northern temperate environment

Wildlife managers design artificial structures, such as bird houses and bat boxes, to provide alternative nesting and roosting sites that aid wildlife conservation. However, artificial structures for wildlife may not be equally efficient at all sites due to varying climate or habitat characteristics influencing thermal properties. For example, bat boxes are a popular measure employed to provide compensatory or supplementary roost sites for bats and educate the public. Yet, bat boxes are often thermally unstable or too cold to fulfill reproductive females needs in northern temperate environments. To help improve the thermodynamics of bat boxes, we tested the effect of (1) three mountings, (2) four orientations, and (3) twelve bat box designs on the internal temperature of bat boxes. We recorded temperatures in bat boxes across a climate gradient at seven sites in Quebec, Canada. Bat boxes mounted on buildings had warmer microclimates at night than those on poles and those facing east warmed sooner in the morning than those facing west or south. Our best new model based on passive solar architecture (Ncube PH1) increased the time in the optimal temperature range (22–40 °C) of targeted species by up to 13% compared to the most commonly used model (Classic 4-chamber) when mounted on a building with an east orientation (other designs presented in the Supplementary Information). Based on bioenergetic models, we estimated that bats saved up to 8% of their daily energy using the Ncube PH1 compared to the Classic 4-chamber when mounted on a building with an east orientation. We demonstrate that the use of energy-saving concepts from architecture can improve the thermal performance of bat boxes and potentially other wildlife structures as well.

Avoiding a conservation pitfall: Considering the risks of unsuitably hot bat boxes

AbstractBat boxes are commonly deployed to mitigate the loss of bat roosting habitat. Due to a dearth of microclimate research, numerous untested commercially available bat boxes, and the uncertain impacts of a rapidly changing climate, the overheating risk presented to bats by bat boxes is largely unquantified. Based on limited research, we know many boxes overheat (i.e., temperatures >40°C). A lack of standardized protocols to evaluate microclimate and misleading information available to the public leads to a murky understanding of risks involved with deploying bat boxes. Herein, we evaluate the thermal tolerance of temperate‐zone bats, delineate areas of concern regarding the risks to temperate‐zone bats when bat boxes are deployed, identify strategies for reducing overheating risk, suggest methods for assessing microclimate, and provide a visual framework to assess overheating risk. Identifying suitable design and placement combinations is crucial to developing region‐specific strategies to mitigate against overheating. We urge consideration of the risks involved with using bat boxes, advocate for rigorous testing before deployment, and suggest using alternatives when possible.

The common noctule bat (Nyctalus noctula): population trends from artificial roosts and the effect of biotic and abiotic parameters on the probability of occupation

AbstractAs urbanization and intense forestry management are increasing, natural bat roosting opportunities, e.g. tree cavities, are constantly declining. A common management practice, especially in urban environments, is the installation of bat boxes. We assessed (1) abundance trends inside artificial bat boxes of the noctule bat (Nyctalus noctula) over 11 years in Neu-Ulm, Germany, and identified (2) parameters affecting the occupation rate. Further, we compared (3) abundance of noctule bats in bat boxes between areas with large availability of natural roosts (forests) and urban areas with primarily artificial roosting structures (parks). Our results revealed a severe decline of noctule bats over 11 years. Further, our results indicate that bat boxes cannot fully replace natural tree cavities. Nonetheless, they support roost availability in areas already altered and providing only low amounts of natural bat roosts. The findings of our study have important implications for the conservation of bats in urbanized landscapes and underline the importance of old and intact forests for local biodiversity.