Roost Trees Research Articles

Divergent Roosting Habits of Rafinesque's Big-eared Bat and Southeastern Myotis During Winter Floods

Despite the importance of winter roosts to bat ecology, much less is known about tree roosts used by bats in winter than in summer. Rafinesque's big-eared bat (Corynorhinus rafinesquii) and southeastern myotis (Myotis austroriparius) are species of concern whose winter tree roost selection may be constrained by seasonal flooding in cypress-gum swamps. To evaluate winter roost selection by these species, we compared characteristics of winter roosts to trees not occupied in winter and to summer roost trees in the Oconee River floodplain, Laurens County, Georgia. We located 23 Rafinesque's big-eared bat winter roosts and 5 southeastern myotis winter roosts by climbing and visually inspecting hollow trees and by radio telemetry. We analyzed differences between used and unused trees in winter and between winter and summer roosts. Despite extensive flooding in winter, Rafinesque's big-eared bats roosted in cypress-gum swamps in summer and winter. Accordingly, they used similar large hollow water tupelo (Nyssa aquatica) in both seasons, although roost entrances were higher in winter. In contrast, southeastern myotis roosted in cypress-gum swamps in summer and switched to a diverse hardwood floodplain forest with shallower flood waters in winter. As a result they used smaller roosts in different tree species in winter than in summer. The divergent roosting habits in winter are likely due to the height of roost entrances in relation to flood waters. In summer Southeastern myotis use basal openings that are submerged during winter flooding, whereas Rafinesque's big-eared bats use openings located higher on the tree bole that are not submerged. Therefore, management for southeastern myotis may require provision of separate summer and winter roosting habitats.

Post-Cranial Hairs in Four Families of Bats

This study identifies the presence of specialized post-cranial hairs on 66 species of bats, and speculates on their significance. While examining museum bat specimens, three main suspected sensory types of hair were discovered: toe hairs, rump hairs, and uropatagial hairs. Life history traits such as day roost type, size of roosting group, and diet were compared with the presence or absence of these hairs using Spearman's Rho tests. The presence of post-cranial hairs was extremely variable across families and genera, making their function difficult to infer. Nevertheless, our tests revealed statistically significant correlations between the presence of uropatagial hairs and using small roosts and the presence of rump hairs and using hollow tree roosts. We suggest that rump hairs may play an important role in roost navigation, while uropatagial hairs may contribute to landing or foraging abilities, especially when found on tailless bats. Toe hairs are suspected to aid in grooming. Histological analysis and further behavioral data are needed to ascertain the functional role of these post-cranial hairs.

Roost selection in suburban bushland by the urban sensitive batNyctophilus gouldi

The persistence of wildlife in fragmented landscapes is predicted to rely on the presence of critical habitat elements. In urban landscapes, the persistence of hollow-dependent bats arguably depends upon the protection of roosting habitat, yet knowledge of bat roosting requirements within these landscapes is limited. We used radiotelemetry to locate day roosts of a species considered sensitive to urbanization, Gould's long-eared bat (Nyctophilus gouldi), in suburban bushland in Sydney, New South Wales, Australia. We compared roost selection data collected for 9 individuals during the mating season (March–April 2009) and 10 individuals during the maternity season (November–December 2009). We found 41 roosts of N. gouldi under decorticating bark and in tree hollows, which were all located in 1 suburban bushland reserve (∼40 ha), with roosts rarely located elsewhere, despite the abundance of available trees in smaller patches outside of the reserve. N. gouldi displayed a clear preference for trees with a greater amount of understory and canopy cover, and only roosted where the extent of forest cover in the local landscape was greatest. Maternity roosts also were predominately located in gullies, and closer to creek lines than expected. Roost switching differed significantly between seasons, with lactating females switching roosts significantly more often than nonlactating females, where roost switching occurred after 1 day on 71% of occasions. Because competition with other fauna for hollows has been suggested as a potential threat, systematic observations of hollow-using bird species, including rainbow lorikeets (Trichoglossus haematodus), were conducted. We observed birds occupying bat roosts on days following bat occupancy, and bats roosted in trees where there were fewer hollow-using birds than randomly available trees. We recommend that further examination of hollow competition be undertaken because abundant, urban-adapted, hollow-nesting birds may render hollows a limiting resource to hollow-users such as bats in urban landscapes. Protection of a network of potential roost trees in suburban bushland remnants, particularly along creek lines, will assist in maintaining this critical resource for bats.

Effects of sunlight on behavior and 25-hydroxyvitamin D levels in two species of Old World fruit bats

It has long been accepted that most vertebrate animals meet their vitamin D requirements from exposure of skin to UV-B (UV-B) radiation. Many factors affect this endogenous synthesis of vitamin D, including season, latitude, time of day, age, presence of hair, and degree of skin pigmentation. Most bats roost in dark places by day and forage at night, and thus have little or no potential for sunlight exposure. Notwithstanding, some tropical species are diurnal and are known to roost in the canopy of trees where they may be exposed to sunlight for up to 12 h each day. In this study, two species of captive tropical bats (both species are active at night but one, Rousettus aegyptiacus, roosts in caves, tombs, and buildings, whereas the other, Pteropus hypomelanus, roosts in trees) were evaluated for their ability to endogenously synthesize vitamin D. Following timed periods of sunlight exposure, blood plasma was analyzed using a competitive protein binding assay (CPBA) to determine concentrations of 25-hydroxyvitamin D [25(OH)D], the major circulating vitamin D metabolite. The ability to photoconvert provitamin D (7-dehydrocholesterol, 7-DHC) in the sub-tropical winter was determined using sunlight exposed borosilicate samples of 7-DHC in hourly increments. Finally, both species were evaluated in their preference for a roost site by the release of individuals into sunlight or shade in timed trials. Our results support the hypotheses: (1) when exposed to natural sunlight, both species exhibited an ability to endogenously synthesize vitamin D, although significant differences were found between the two, (2) photoconversion of 7-DHC to previtamin D3 is possible during the mid-day hours of a sub-tropical winter day and (3) captive, cave roosting R. aegyptiacus will choose shaded roost sites while captive P. hypomelanus will show no preference for either shade or sun.

Resource partitioning in three syntopic forest-dwelling European bat species (Chiroptera: Vespertilionidae)

Resource partitioning in syntopic bats is mainly studied through comparative ecomorphology and behavioural ecology. We used simultaneous radio-tracking of syntopic forest-dwelling bats, the western barbastelle (Barbastella barbastellus), Bechstein’s bat (Myotis bechsteinii) and the brown long-eared bat (Plecotus auritus) to analyse individual and species-specific foraging habitat and roost site selection. We estimated niche partitioning through Euclidean distance analyses to landscape elements and through Pianka’s niche overlap index for roost types. We analysed a total of 2278 fixes and 54 roosts of 15 bats. Western barbastelles and Bechstein’s bats foraged significantly closer to the forest than brown long-eared bats. Female barbastelles also foraged significantly closer to forest tracks, which were avoided by female brown long-eared and Bechstein’s bats. Female and male brown long-eared bats were found close to open habitats, which were avoided by the other two species. We found a high niche overlap in terms of roost height, but low overlap in terms of roost type and roost tree species among the three bat species. Individual niche variation may allow these specialised forest-dwelling bat species to minimise competition when foraging and roosting in syntopy.

Mangroves as maternity roosts for a colony of the rare east-coast free-tailed bat (Mormopterus norfolkensis) in south-eastern Australia

Context Maternity roosts of insectivorous bats (where females raise young) are critical to the conservation of threatened species as roost quality can influence reproductive success. Additionally, threatened species may have specialised requirements or unusual behaviour, which may be overlooked without targeted investigation. Aims To explore which factors influence the roost selection of Mormopterus norfolkensis, by comparing day roosts, identified via radio-tracking, with environmental variables collected at tree, patch and landscape scales. Methods We collected a range of variables describing maternity roosts and surrounding patches, including internal measurements of hollows and microclimate. Additionally, we derived landscape-scale variables using a geographic information system. We then explored which variables best explained roost occurrence using logistic regression. Key results Nineteen lactating females and two male M. norfolkensis were tracked to 40 roost trees, mostly grey mangrove, Avicennia marina subsp. australasica. Lactating females were found to be faithful to two patches of mangrove forest close to where they were captured, regularly switched roosts and roosted in hollows singularly or in small groups. The attributes of mangrove patches, especially a high proportion of hollows, better predicted roosting by lactating females than roost-tree or landscape characteristics. Additionally, although the microclimate of roost hollows was not significantly different from ambient mangrove conditions, the mangrove forest was slightly more stable and had higher humidity than did other nearby habitats. Conclusions Contrary to predictions, maternity roosting group sizes were relatively small, indicating that bats were not deriving thermoregulatory benefits from communal living. However, we suggest that lactating females may benefit from the operation of a fission–fusion society among the colony as a whole. Additionally, the mature mangrove forest could offer unique roosting opportunities for bats because they support high densities of hollow-bearing trees, a stable microclimate and potentially low abundances of predators and competitors. Implications This is one of few international bat–mangrove studies and it illustrates that threatened species can behave unexpectedly and may be overlooked in conservation strategies that are based largely on anecdotal observations. We encourage further research into the value of mangrove forests to terrestrial fauna globally.

Summer heterothermy in Rafinesque’s big-eared bats (Corynorhinus rafinesquii) roosting in tree cavities in bottomland hardwood forests

Many small mammals are heterothermic endotherms capable of maintaining an elevated core body temperature or reducing their thermoregulatory set point to enter a state of torpor. Torpor can confer substantial energy savings, but also incurs ecological costs, such as hindering allocation of energy towards reproduction. We placed temperature-sensitive radio transmitters on 44 adult Rafinesque's big-eared bats (Corynorhinus rafinesquii) and deployed microclimate dataloggers inside 34day roosts to compare the use of torpor by different sex and reproductive classes of bats during the summer. We collected 324 bat-days of skin-temperature data from 36 females and 4 males. Reproductive females employed fewer torpor bouts per day than non-reproductive females and males (P<0.0001), and pregnant and lactating females had higher average (P<0.0001) and minimum (P<0.0001) skin temperatures than non-reproductive females. Pregnant females spent less time torpid (P<0.0001) than non-reproductive females, but lactating females used relatively deep, long torpor bouts. Microclimates varied inside tree species with different configurations of entrances to the roost cavity (P<0.0001). Bats spent more time torpid when roosting in water tupelo (Nyssa aquatica) trees possessing only a basal entrance to the cavity (P=0.001). Of the tree species used as roosts, water tupelo cavities exhibited the least variable daytime and nighttime temperatures. These data demonstrate that use of summer torpor is not uniform among sex and reproductive classes in Rafinesque's big-eared bat, and variation in microclimate among tree roosts due to species and structural characteristics facilitates the use of different thermoregulatory strategies in these bats.

Cat predation of short-tailed bats (Mystacina tuberculata rhyocobia) in Rangataua Forest, Mount Ruapehu, Central North Island, New Zealand

Cats (Felis catus) are known predators of New Zealand bats, although all records to date have been from domestic cats thought to have caught foraging bats. We outline the first evidence of predation of short-tailed bats (Mystacina tuberculata rhyocobia) at a roost tree. A total of 156 individual bat wings (78 pairs) and 22 intact bodies were found at the base of two colonial roost trees in Rangataua Forest on the southern slopes of Mount Ruapehu, Central North Island in New Zealand, over a period of 7 days. Assuming a pair of wings belonged to one individual, at least 102 bats were killed by a male cat caught in a live trap at the base of one roost tree. No more deaths were recorded after its capture.

Summer tree roost selection by Rafinesque's big‐eared bat

AbstractRoost requirements of most North American forest bats are well‐documented, but questions remain regarding the ultimate mechanisms underlying roost selection. Hypotheses regarding roost selection include provision of a stable microclimate, space for large colonies, protection from predators, and proximity to foraging habitat, among others. Although several hypotheses have been proposed, specific mechanisms likely vary by species and geographic region. Rafinesque's big‐eared bat (Corynorhinus rafinesquii) commonly roosts in trees with large basal hollows in the Coastal Plain of the southeastern United States. Our objective was to weigh evidence for hypotheses regarding selection of diurnal summer roosts by Rafinesque's big‐eared bat at 8 study sites across the Coastal Plain of Georgia, USA. We used transect searches and radiotelemetry to locate roosts and measured 22 characteristics of trees, tree cavities, and surrounding vegetation at all occupied roosts and for randomly selected unoccupied trees. We evaluated 10 hypotheses using single‐season occupancy models and used Akaike's information criterion to select the most parsimonious models. We located 170 tree roosts containing approximately 870 bats for our analysis. The best supported model predicted bat presence from cavity size, interior wall texture, and number of entrances. Because large cavities allow bats to fly and smooth walls impede attacks by terrestrial predators, our results are consistent with the hypothesis that bats select roosts that allow them to evade predators. However, data on predation rates are needed for a conclusive determination. Because trees suitable as roosts for Rafinesque's big‐eared bat are rare in the landscape, protection of suitable forested wetland habitat is essential to provide current and long‐term roost tree availability. © 2012 The Wildlife Society.

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.

Forest Succession and Maternity Day Roost Selection byMyotis septentrionalisin a Mesophytic Hardwood Forest

Conservation of summer maternity roosts is considered critical for bat management in North America, yet many aspects of the physical and environmental factors that drive roost selection are poorly understood. We tracked 58 female northern bats (Myotis septentrionalis) to 105 roost trees of 21 species on the Fort Knox military reservation in north-central Kentucky during the summer of 2011. Sassafras (Sassafras albidum) was used as a day roost more than expected based on forest stand-level availability and accounted for 48.6% of all observed day roosts. Using logistic regression and an information theoretic approach, we were unable to reliably differentiate between sassafras and other roost species or between day roosts used during different maternity periods using models representative of individual tree metrics, site metrics, topographic location, or combinations of these factors. For northern bats, we suggest that day-roost selection is not a function of differences between individual tree speciesper se, but rather of forest successional patterns, stand and tree structure. Present successional trajectories may not provide this particular selected structure again without management intervention, thereby suggesting that resource managers take a relatively long retrospective view to manage current and future forest conditions for bats.

Roost networks of northern myotis ( Myotis septentrionalis) in a managed landscape

Maternity groups of many bat species conform to fission–fusion models and movements among diurnal roost trees and individual bats belonging to these groups use networks of roost trees. Forest disturbances may alter roost networks and characteristics of roost trees. Therefore, at the Fernow Experimental Forest in West Virginia, we examined roost tree networks of northern myotis ( Myotis septentrionalis) in forest stands subjected to prescribed fire and in unmanipulated control treatments in 2008 and 2009. Northern myotis formed social groups whose roost areas and roost tree networks overlapped to some extent. Roost tree networks largely resembled scale-free network models, as 61% had a single central node roost tree. In control treatments, central node roost trees were in early stages of decay and surrounded by greater basal area than other trees within the networks. In prescribed fire treatments, central node roost trees were small in diameter, low in the forest canopy, and surrounded by low basal area compared to other trees in networks. Our results indicate that forest disturbances, including prescribed fire, can affect availability and distribution of roosts within roost tree networks.

Nocturnal Activity Patterns of Northern Myotis (Myotis septentrionalis) during the Maternity Season in West Virginia (USA)

Nocturnal activity patterns of northern myotis (Myotis septentrionalis) at diurnal roost trees remain largely uninvestigated. For example, the influence of reproductive status, weather, and roost tree and surrounding habitat characteristics on timing of emergence, intra-night activity, and entrance at their roost trees is poorly known. We examined nocturnal activity patterns of northern myotis maternity colonies during pregnancy and lactation at diurnal roost trees situated in areas that were and were not subjected to recent prescribed fires at the Fernow Experimental Forest, West Virginia from 2007 to 2009. According to exit counts and acoustic data, northern myotis colony sizes were similar between reproductive periods and roost tree settings. However, intra-night activity patterns differed slightly between reproductive periods and roost trees in burned and non-burned areas. Weather variables poorly explained variation in activity patterns during pregnancy, but precipitation and temperature were negatively associated with activity patterns during lactation.

Recent infestation of forest stands by spruce beetles does not predict habitat use by little brown bats ( Myotis lucifugus) in southwestern Yukon, Canada

Insect outbreaks affect forest structure which may have significant effects on the habitat of other animals. Forest-dwelling insectivorous bats are likely affected by associated changes in the abundance of roost trees and insect prey, altered foraging and flying efficiency, and predation risk. We examined the short-term effects (3-13 years post-infestation) of an outbreak of spruce beetles ( Dendroctonus rufipennis) on the habitat use of little brown bats ( Myotis lucifugus) in the boreal forest of the southwestern Yukon, Canada. We measured bat activity, using Anabat II bat detectors, in 90 forested stands that had experienced from 0 to 90% tree mortality due to spruce beetles. We used generalized linear models to assess whether bat activity varied with tree mortality, season, tree density, canopy closure, or distance to the nearest lake or town. Bat activity did not vary significantly with tree mortality, season, or canopy closure, but decreased with increasing tree density. Bat activity was significantly greater in areas close to both the nearest lake and nearest town, and was low in areas that were far from either. Our results indicate that in the short-term, habitat use by little brown bats was not related to the severity of spruce beetle infestation, but suggest that in the long-term, bats may be positively affected by decreased tree density as beetle-killed trees fall down.

Use of lichen as a roosting substrate by Perimyotis subflavus, the tricolored bat, in Nova Scotia

An apparently disjunct population of tricolored bats (Perimyotis subflavus) exists in southwest Nova Scotia. During the summers of 2003–2004 and 2007–2008 we trapped bats in mist nets set at a bridge over the Mersey River in Kejimkujik National Park. In total we captured 42 tricolored bats (41 female and 1 male) and fitted 32 females and the single male with radio transmitters and tracked them to their roost sites daily. Characteristics of roost sites were compared to those of randomly selected, potentially available roost sites using an a priori-selected candidate set of models and ranked using AICc for model selection. In total we found 99 unique roost trees in 9 spatially distinct (8 female, 1 male) roosting areas. On average, bats spent 2.5 d in a roost tree. While conspecifics from other parts of the species' range typically roost in tree foliage, maternity colonies of tricolored bats in Nova Scotia roosted exclusively in Usnea trichodea lichen, typically in conifers (of which 91% were spruce; Picea spp.) that were on average 212 m from water. Only 4% of the 300 random trees from the landscape contained Usnea trichodea. These trees were a mixture of softwood and hardwood (58% and 42%, respectively) and were, on average, 550 m from water. These findings represent an apparently unique relationship between lichens and bats that likely impacts many aspects of the species biology, including distribution, social structure, and parasite prevalence.

Roost Selection by Male Indiana Myotis Following Forest Fires in Central Appalachian Hardwoods Forests

AbstractDespite the potential for prescribed fire and natural wildfire to increase snag abundance in hardwood forests, few studies have investigated effects of fire on bat roosting habitat, particularly that of the endangered Indiana myotis Myotis sodalis. From 2001 to 2009, we examined roost selection of Indiana myotis in burned and unburned forests in Tucker County, West Virginia. We radiotracked 15 male Indiana myotis to 50 roost trees; 16 in burned stands and 34 in unburned stands. Indiana myotis roosted in stands that had initially been burned 1–3 y prior to our observations. In burned stands, Indiana myotis roosted exclusively in fire-killed maples (Acer spp.). In unburned stands, they roosted in live trees, predominately hickories (Carya spp.), oaks (Quercus spp.), and maples. Roost trees in burned stands were surrounded by less basal area and by trees in advanced stages of decay, creating larger canopy gaps than at random trees in burned stands or actual roost trees located in unburned stands. Compared to random trees in unburned stands, roost trees in unburned stands were less decayed, had higher percent bark coverage, and were surrounded by less basal area, also resulting in larger canopy gaps. Roost-switching frequency and distances moved by Indiana myotis among roost trees were similar between burned and unburned stands. Our research indicates that use of fire for forest management purposes, at minimum provoked no response from Indiana myotis in terms of roost tree selection, and may create additional roost resources, depending on spatial context.

Roost site selection by southern forest bat Vespadelus regulus and Gould's long-eared bat Nyctophilus gouldi in logged jarrah forests; south-western Australia

Information on roosting requirements and responses to forest management is integral to effectively conserve and manage bat populations. Tree hollows are especially important for roosting bats given the long time taken for hollows to form. We used radiotelemetry to compare roost site selection in two species, Vespadelus regulus and Nyctophilus gouldi, in logged jarrah forests of south-western Australia. We compared characteristics of roost trees and forest structure around roost trees (n=48) with randomly located plots at a local roost tree level (n=90) in February and March 2009. For landscape features, we compared roost trees with randomly selected trees in the broader landscape that had cavities or exfoliating bark (n=204). V. regulus roosted solely in hollows that were located predominantly in contemporarily unlogged buffers and mature forest while N. gouldi used a broader range of roost types, located in contemporarily unlogged buffers and mature forest and in retained habitat trees in gap release and shelterwood creation silvicultural treatments. In contrast with N. gouldi, which selected hollows or crevices under bark near the ground and close to vegetation, V. regulus used hollows that were high above ground and had little surrounding vegetation. Both species preferred large trees, in intermediate or advanced stages of decay and crown senescence. Bats changed roosts frequently, with short distances between subsequent roosts, suggesting a degree of spatial fidelity. Contemporarily unlogged buffers and mature forest contained higher densities of trees with hollows than gap release and shelterwood creation areas, potentially providing more alternate bat roosts. Our results demonstrate the importance of mature forest and unlogged buffers as bat roost sites in logged jarrah forests of south-western Australia, but the area of old forest required by these and co-occurring bat species remains to be determined.

Divergent Microclimates in Artificial and Natural Roosts of the Large-Footed Myotis (Myotis macropus)

The thermal environment of day roosts is considered one of the most influential factors affecting the survival, growth and reproduction of microbats. The use of torpor is a common energy saving strategy employed by microbats in temperate regions. The efficiency of entry into, and arousal from, torpor is governed by roost microclimate, primarily roost temperature. The large-footed myotis Myotis macropus roosts in both tree cavities and a man-made tunnel at Yan Yean reservoir in Victoria, Australia. We investigated the thermal properties of both roost types in comparison to available tree cavities and ambient temperature over four time periods from October 2003 to May 2005. Tree cavities and tunnel roosts remained significantly warmer at night, cooler during the day, and were more stable than ambient temperatures. In addition, roost tree cavities were significantly cooler between 10:00–13:00 h compared to available tree cavities, and there was a trend for roost tree cavities to be slightly warmer at night a...

Interannual Fidelity to Roosting Habitat and Flight Paths by Female Western Barbastelle Bats

The roost area selection of reproductive female western barbastelles was examined throughout four study seasons (2004–2007) via radio-tracking and automated acoustic monitoring. We specifically analysed the spatial structure of the roosting habitat and roost fidelity including a flight path connecting the roosts. We radio-tracked 13 colony members to 46 natural roosts, mainly dead oaks with large pieces of loose bark. Simultaneous tracking of four pairs of females revealed the existence of subgroups and fission-fusion-behaviour in Barbastella barbastellus. The colony displayed fidelity to the roost area rather than to single roost trees, although some trees were reused in two or three study seasons. Bimodal activity patterns obtained from acoustic monitoring indicated that the flight path connecting two core roosting areas functioned as a commuting corridor.

Plantation forests are used by the lesser short-tailed bat, Mystacina tuberculata rhyacobia

Lesser short-tailed bats, Mystacina tuberculata rhyacobia, use Pinus radiata plantation forests within the central North Island of New Zealand for foraging, commuting, and roosting. These plantations are generally contiguous with a large native forested area from which this species is already known. Short-tailed bats have been detected using native remnants and reserves within plantations, and have been radio-tracked to long-dead native tree roosts within young Pinus radiata stands. We provide the first list of exotic plantations known to be used by short-tailed bats.