Roost Trees Research Articles

Population Structure and Sex-biased Dispersal in the Forest Dwelling Vespertilionid Bat, Myotis Septentrionalis

Sex-biased dispersal is a specific pattern of movement whereby one sex either stays or returns to its natal group or natal area to breed while the other disperses from the natal area. Temperate vespertilionid bats are thought to exhibit the typical mammalian pattern of male-biased dispersal although relatively few studies have been conducted on this group. The northern myotis (Myotis septentrionalis) is a relatively common forest dwelling bat found in eastern North America. Despite being a common species in North America, relatively little is known about its habitat requirements and life history characteristics including dispersal patterns. Using five polymorphic microsatellite loci I found that females within localized subpopulations exhibited a higher degree of genetic structuring than males indicating female philopatry and male-biased dispersal [female FST = 0.011; male FST = −0.016; P = 0.006 (sex-biased dispersal randomization test)]. I also found a weak (FST = 0.002), but significant (P = 0.03), average fixation index for the subpopulations examined which is consistent with other studies on temperate vespertilionid bats. The presence of maternity site fidelity in M. septentrionalis may have important conservation implications since commercial and private development that thins or removes potential roost trees could have an impact on pregnant female bats that will have to incur additional costs of searching for new roosting habitat as they return from their hibernacula.

HAIRY WOODPECKER WINTER ROOST CHARACTERISTICS IN BURNED PONDEROSA PINE FOREST

Abstract Winter roosts afford escape from extreme climatic conditions, reduce heat and energy loss, and provide protection from predators for North American woodpeckers. We monitored the use and characteristics of 12 winter roosts used by nine radio-marked Hairy Woodpeckers (Picoides villosus) in ponderosa pine (Pinus ponderosa) forests of northern Arizona that had experienced wildfire in 1996 and 2000. Roost trees were larger in diameter than 95% of non-roost trees and on average 2.5 times larger within burned areas of similar severity. Roost trees were within patches less dense than 95% of measured patches across study sites, which were on average 1.5 times as dense. Two-thirds of roost trees were created by fire and were smaller than those created by other means. Six birds each used one roost and three males each used two roosts. Two-thirds of the roosts were outside or on the edge of estimated home ranges. Maximum straight-line distances traveled, from roost to farthest point of home range, were >1 km...

Winter Roosting Ecology of Eastern Red Bats in Southwest Missouri

Abstract:Eastern red bats (Lasiurus borealis) have been found to overwinter in areas that can experience severe fluctuations in temperature. We examined the red bat's use of winter roosts in southwest Missouri, USA, for 2 winters (2003–2005). We found tree roosts in eastern red cedars (Juniperus virginiana) and hardwoods. Tree roost sites were located on the south side of trees, and we found roost trees on south‐facing slopes. Roost sites occurred more frequently in the location with least canopy cover. Bats switched from tree roosts to leaf litter roosts when ambient temperatures approached or fell below freezing. We found habitat characteristics and aspect to be determining factors in the selection of leaflitter roosts. Management of overwintering red bats requires a diverse forest structure, including canopy gaps, stand‐density variation, and leaf‐bearing trees, including oaks (Quercusspp.).

FEEDING ECOLOGY OF TAWNY OWL (STRIX ALUCO) IN WIGRY NATIONAL PARK (NORTH EAST POLAND)

In 1989–1991, the feeding ecology of Tawny Owl (Strix aluco) was studied in Wigry National Park (NE Poland). Diet composition was investigated by analysis of pellets gathered in stands under roost trees or nest boxes from April to August in 3-5 home ranges each year. In order to assess potential prey, small animals were caught in 28 traps. Small mammals composed 66.5% of prey items and 78.9% of food biomass of Tawny Owl, birds - 8.1% and 13.9%, and frogs - 17.4% and 6.8% of prey and biomass, respectively. The diet was dominated by rodents, mainly bank vole (Clethrionomys glareolus) and common vole (Microtus arvalis), which together composed 37.0% of prey items and 37.2% of the biomass consumed. Among birds, the most common prey was Song Thrush (Turdus philomelos). Slightly preferred prey were field mouse (Apodemus agrarius), short-tailed vole (Microtus agrestis) and bank vole. One pellet contained 1-11 (mean 2.34 ± 0.09) prey items. Amphibians were the most numerous during May and June.

Roosting behaviour of the greater noctule Nyctalus lasiopterus Schreber, 1780 (Chiroptera, Vespertilionidae) in Hungary as revealed by radio-tracking

Nyctalus lasiopterus is one of the rarest bat species in Europe and there is little information on the roosting requirements and habitat preference of this species. In recent times two papers have been published regarding carnivory of small birds by the species (Dondini and Vergari 2000, Ibanez et al. 2001). In these articles some notes are also presented on the roosts of the species and Ibanez et al. (2004) give a summary on the knowledge of the ecology of N. lasiopterus, including data on roosting behaviour. N. lasiopterus is known as a typical tree-dwelling bat, roosting in trees all year round. It has been found in the cavities of very different trees, including both deciduous and coniferous species (Ibanez et al. 2004). Dondini and Vergari (2000) reported the species from bat boxes fitted on beech trees (Fagus sylvatica) in Tuscany, Italy. Ibanez et al. (2001, 2004) found 11 tree roosts of N. lasiopterus in a park in Sevilla, eight of which were in Platanus spp. and three in Sophora japonica. They also described a maternity colony of 80 specimens roosting under the dried leaves of three palm trees (Washingtonia filirifera) in Jerez de la Frontera, Southern Spain. Beck and Gebhard (2000) reported on an unusual occurrence of the species: a female specimen was found in the cellar of a castle in Aargau Kanton, Switzerland. Another subterranean occurrence was discovered by Tvrtkovic and Baltic (1996), where the remains of 16 N. lasiopterus were found in a cave on the island of Mljet, Croatia. N. lasiopterus is known from nine locations in Hungary (Vasarhelyi 1964, Topal 1959, 1976, Dobrosi 1993, Gombkoto et al. 1996, Czajlik and Harmos 1997, Cser kesz 1998, Matis et al. 2003), but no roosts have been reported. However, one partly destroyed corpse of N. lasiopterus was found in an attic in Hungary (Topal 1976), but this might have been captured and transported postmortem to the building by Tyto alba. One of the Hungarian localities of N. lasiopterus is a significant place of occurrence, which gives the opportunity to observe the species regularly. In 2004, a radio telemetry programme was initiated with the main aim of finding the roosts of N. lasiopterus and ensuring their conservation. This paper reports the first results concerning the roosting behaviour of the species.

Predicting Minimum Habitat Characteristics for the Indiana Bat in the Champlain Valley

Predicting potential habitat across a landscape for rare species is extremely challenging. However, partitioned Mahalanobis D2 methods avoid pitfalls commonly encountered when surveying rare species by using data collected only at known species locations. Minimum habitat requirements are then determined by examining a principal components analysis to find consistent habitat characteristics across known locations. We used partitioned D2 methods to examine minimum habitat requirements of Indiana bats (Myotis sodalis) in the Champlain Valley of Vermont and New York, USA, across 7 spatial scales and map potential habitat for the species throughout the same area. We radiotracked 24 female Indiana bats to their roost trees and across their nighttime foraging areas to collect habitat characteristics at 7 spatial scales: 1) roost trees, 2) 0.1-ha circular plots surrounding the roost trees, 3) home ranges, and 4–7) 0.5-km, 1-km, 2-km, and 3-km buffers surrounding the roost tree. Roost trees (n = 50) typically were tall, dead, large-diameter trees with exfoliating bark, located at low elevations and close to water. Trees surrounding roosts typically were smaller in diameter and shorter in height, but they had greater soundness than the roost trees. We documented 14 home ranges in areas of diverse, patchy land cover types that were close to water with east-facing aspects. Across all landscape extents, area of forest within roost-tree buffers and the aspect across those buffers were the most consistent features. Predictive maps indicated that suitable habitat ranged from 4.7–8.1% of the area examined within the Champlain Valley. These habitat models further understanding of Indiana bat summer habitat by indicating minimum habitat characteristics at multiple scales and can be used to aid management decisions by highlighting potential habitat. Nonetheless, information on juvenile production and recruitment is lacking; therefore, assessments of Indiana bat habitat quality in the region are still incomplete.

Potential for Niche Overlap in Roosting Sites Between Nycticeius humeralis (Evening Bats) and Eptesicus fuscus (Big Brown Bats)

Many bat species have similar requirements for summer roosting sites leading to the potential for niche overlap and competition for roosts. Similarities in day roosts between bat species are rarely considered as a factor influencing population dynamics of species. We tracked Nycticeius humeralis (evening bats) and Eptesicus fuscus (big brown bats) to roost trees to evaluate the possibility of niche overlap in roost-site selection. Only tree height was significantly different between roosts used by the two species. Canopy cover, canopy height, dbh, tree species, tree condition, and roost type were not significantly different between the trees used by the two species. If competition for roosts exists between these species, similarities in roost trees may be important, especially as roost trees become scarce due to increased human alteration of roosting habitat. Competition for roost sites, in concert with other factors, may affect both competitors; however, populations of the inferior competitor, which is probably the evening bat, should be more negatively affected.

Introduction to the Special Section—Bat Habitat Use in Eastern North American Temperate Forests: Site, Stand, and Landscape Effects

Forest bats of eastern North America select habitats for roosting, foraging, and winter hibernation/migration over a myriad of scales. An understanding of forest-bat habitat use over scales of time and space is important for their conservation and management. The papers in this Special Section report studies of bat habitat use across multiple scales from locations across the eastern forests of North America. The consensus of the studies in the Special Section is that the larger portion of the variability in bat habitat use occurs at the smaller scales of sites (roost trees) and stands (foraging areas). Nevertheless, it was also recognized that these features occur discontinuously across larger-scale watersheds and landscapes.

Roost selection flexibility of European starlings aids invasion of urban landscape

The ability to shift habitat preferences is one of the characteristics of flexibility in a species and can be a key to the success of invasive species. Our objective in this paper was to analyse the possible behavioural flexibility of European starling ( Sturnus vulgaris) through its rapid adjustment to changes in roost site availability. First we analysed the change of starling roost sites at regional (Brittany, 1973–1997, 87 sites) and at town scales (Rennes, 1983–2004, 59 sites) in western France. Site selection followed changes in habitat availability, switching from reed beds to conifer plantations regionally, and from hedges/bushes to trees, especially conifers, in Rennes. Secondly, we analysed urban roost sites measuring several characteristics of trees and neighbouring environment. Roost trees were taller and had a bole circumference and canopy larger than non-roost trees. Trees with a large amount of small branches were more selected by starlings. Among environmental features including landscape composition and configuration, only temperature was higher in roost sites. Starlings show great flexibility in choice of roost site characteristics which may in part explain their success as an invasive species and as urban colonists. Despite such flexibility, preferred roost site characteristics could be used to reduce urban nuisance by managing/creating sites in less sensitive locations.

Diet of the Myotis sodalis (Indiana Bat) at an Urban/Rural Interface

We conducted a study of the diet of the federally endangered Indiana bat (Myotis sodalis) at an urban/rural interface near Indianapolis International Airport in summer 2004. We used two 1-m2 quadrats covered with window screening to collect guano under a known roost tree. We then examined 20 fecal pellets/week until the bats abandoned the roost (i.e., 13 weeks). The most common orders of insects eaten were: Lepidoptera (35.3% volume, 84.6% frequency), Diptera (27.9%, 73.2%), Coleoptera (16.9%, 62.9%), and Hymenoptera (10.9%, 45.9%). Components of the diet at the ordinal level varied significantly over time. Despite the developed nature of the site, the diet consisted of the same components reported in earlier studies.

Autumn Activity of Myotis sodalis (Indiana Bat) in Bland County, Virginia

Nocturnal activity and diurnal roosts of Myotis sodalis (Indiana bat) were studied during autumn swarming in 2000 near a hibernaculum in Bland County, VA. Bats were active in 9 habitats, using open deciduous forests more fequently, and developed lands, closed deciduous habitats, and mixed deciduous-evergreen habitats less frequently than would be expected based on random use of available habitats. Agricultural lands, intermediate deciduous forests, old field, and water were used in proportion to availability. Wooded pastures (agricultural) and recently logged areas (open woodland) provided foraging habitat. Many bats used multiple diurnal roosts; twenty-six roosts were found in 9 species of trees. Five bats, males and females, used the same roost tree for 2–3 consecutive days. Many roosts were near canopy openings; ten were in selective cut, clear-cut, and pastured woodlands with scattered trees and open canopies, and 5 were near or along logging roads or powerline corridors with open canopies. Eleven roosts were in forests with moderate to high canopy closure. Roosts were clumped near the cave (mean = 0.8 km; SD = 0.3). Roosts closer to the cave,, although limited in number, may provide an advantage during swarming. Prolonged wet, cold weather systems appear to be a part of the seasonal cycle that drives timing of autumn swarming.

House Finch Carpodacus mexicanus roosting behaviour during the non‐breeding season and possible effects of mycoplasmal conjunctivitis

We studied House Finch Carpodacus mexicanus roosting behaviour during the non‐breeding season using radiotracking and direct observations in Ithaca, NY, USA. In contrast to what has been reported in the literature and in contrast to what should be expected from Newton's European studies of cardueline finches, House Finches roost in small groups (mean 3.5; maximum 11) and do not display at roost sites. Seventy‐seven per cent of the birds re‐used the same tree on successive observations. In winter, birds re‐used the same roost tree more often than in the autumn, and birds with mycoplasmal conjunctivitis tended to move more between roost trees than did birds without conjunctivitis. A small number of radiotagged birds that roosted in the same tree were observed together in the daytime more often than by chance, suggesting the existence of social bonds between birds (some same sex) during the non‐breeding season. In the autumn the birds often roosted in leafed deciduous trees and closer to their daytime feeding locations than they did in winter. In winter all birds roosted in evergreen trees. It is possible that the reliable and predictable food sources at feeding sites offered by the public might have changed House Finch roosting behaviour.

Applying Network Analysis to the Conservation of Habitat Trees in Urban Environments: a Case Study from Brisbane, Australia

In Australia more than 300 vertebrates, including 43 insectivorous bat species, depend on hollows in habitat trees for shelter with many species using a network of multiple trees as roosts. We used roost-switching data on white-striped freetail bats (Tadarida australis; Microchiroptera: Molossidae) to construct a network representation of day roosts in suburban Brisbane, Australia. Bats were caught from a communal roost tree with a roosting group of several hundred individuals and released with transmitters. Each roost used by the bats represented a node in the network, and the movements of bats between roosts formed the links between nodes. Despite differences in gender and reproductive stages, the bats exhibited the same behavior throughout three radiotelemetry periods and over 500 bat days of radio tracking: each roosted in separate roosts, switched roosts very infrequently, and associated with other bats only at the communal roost. This network resembled a scale-free network in which the distribution of the number of links from each roost followed a power law. Despite being spread over a large geographic area (> 200 km2), each roost was connected to others by less than three links. One roost (the hub or communal roost) defined the architecture of the network because it had the most links. That the network showed scale-free properties has profound implications for the management of the habitat trees of this roosting group. Scale-free networks provide high tolerance against stochastic events such as random roost removals but are susceptible to the selective removal of hub nodes. Network analysis is a useful tool for understanding the structural organization of habitat tree usage and allows the informed judgment of the relative importance of individual trees and hence the derivation of appropriate management decisions. Conservation planners and managers should emphasize the differential importance of habitat trees and think of them as being analogous to vital service centers in human societies.

ROOST SELECTION BY FOREST-LIVING FEMALE BIG BROWN BATS (EPTESICUS FUSCUS)

Previous studies of forest-dwelling bats have identified physical features of trees and forests that correlate with the presence of bats by comparing roost sites to paired, randomly selected sites. This method may be limited if the absence of bats from random sites cannot be confirmed. Our purpose was to address roosting ecology of female big brown bats (Eptesicus fuscus) using a different approach. We quantified relative use of trees with 3 different types of cavity openings (long crevices, multiple holes, or single holes) and compared the relative use of these potential roosts to the availability of each roost type in the study area. Bats used trees with multiple holes and crevices significantly more often than expected based on their availability and trees with single holes less often than expected. Crevice roosts had significantly larger cavities than did single holes and roosting-group size was positively correlated with cavity volume. No relationship was found between cavity volume and tree height or stem diameter of roost trees, 2 variables that have been reported to correlate with roost selection in other studies of forest bats. Examination of our data suggests that the volume of roost cavities may be an important selection criterion for colonial, forest-living bats and that standard interpretations of the roost versus random-tree approach may not accurately identify patterns of roost selection in some systems.

Roost tree characteristics determine use by the white‐striped freetail bat (Tadarida australis, Chiroptera: Molossidae) in suburban subtropical Brisbane, Australia

Abstract We examined factors affecting roost tree selection by the white‐striped freetail bat Tadarida australis (Chiroptera: Molossidae), a large insectivorous bat in suburban Brisbane, Australia. We compared biophysical characteristics associated with 34 roost trees and 170 control trees of similar diameter, height and tree senescence characters. Roost trees used by the white‐striped freetail bat had significantly higher numbers of hollows in the trunk and branches (P < 0.003) and were more likely to contain a large trunk cavity with an internal diameter of >30 cm (P < 0.001) than control trees. These trees also accommodated more species of hollow‐using fauna (P = 0.005). When comparing roost trees with control trees of similar diameters and heights, roost trees were on average at a later stage of tree senescence (P < 0.001). None of the roost trees were found in the large forest reserves fringing the Brisbane metropolitan area despite these areas being used for foraging by the white‐striped freetail bat. Although all tree locations in this study were in modified landscapes, roost trees tended to be surrounded by groups of trees and undergrowth. Roost trees provide important habitat requirements for hollow‐using fauna in suburban, rural and forested environments.

Description of Spring Roost Trees Used by Female Indiana Bats (Myotis sodalis) in the Lake Champlain Valley of Vermont and New York

Extensive effort has been directed at the roosting ecology of the federally endangered Indiana bat (Myotis sodalis) during the maternity season; however, spring roosting ecology has received much less attention. In April 2002, radio transmitters were attached to the back of 19 female Indiana bats as they emerged from a hibernaculum in northeastern New York. Thirty-nine roost trees were found in the vicinity of the Lake Champlain Valley of New York and Vermont over the span of 224 bat days (i.e., 1 bat located for 1 d equals 1 bat day). Distances from hibernaculum to roost trees ranged from 14.6 to 40.0 km (mean = 26.9 km). Shagbark hickory (Carya ovata) was the most common (33.3% of all trees, 39.7% of all bat days) of 11 tree species used. Roost trees had a mean diameter of 45.6 cm, were 18.9 m tall and were similar in structure to those used during summer by Indiana bats elsewhere in their range. This study provides the first large-scale examination of trees used by female Indiana bats after spring emergence, supplying critical life history information useful for the conservation of this species.

Roost site selection by lesser short‐tailed bats (Mystacina tuberculata) in mixed podocarp‐hardwood forest, Whenua Hou/Codfish Island, New Zealand

Roosting ecology of the lesser short‐tailed bats (Mystacina tuberculata) was studied in mixed podocarp‐hardwood forest on Whenua Hou/Codfish Island, New Zealand during winter 1996, and winter to summer 1998–99. The structural characteristics of roosts used by communal groups and by solitary bats are described, and roost selection is examined at three scales: forest stand, tree, and cavity. Differences in structural characteristics and microclimate of roosts used in winter and in summer are compared. Forty‐three bats were radio‐tracked and 122 tree roosts located. Communal groups occupied 47.5% of roosts and solitary bats occupied 52.5%. Bats selected roosts in Hall's totara (Podocarpus hallii) trees more than expected based on the availability of this tree species. Roost trees had significantly larger stem diameters and greater numbers of cavities than random trees. Communal bats demonstrated a higher degree of roost selectivity than solitary bats. Communal roosts had significantly less vegetation clutter surrounding roost entrances, larger stem diameters at cavity height, larger internal cavity heights, and thicker cavity walls than potentially available cavities. Communal roost cavities were consistently larger than solitary roosts. Solitary roosts had less open space around them than communal roosts and random cavities. Communal roosts were well insulated and exhibited stable internal temperatures. Structural and thermal characteristics did not differ between roosts used in winter and in summer. Differences between characteristics of communal and solitary roosts, and selection of well‐insulated cavities in some of the largest available trees, appears consistent among different forest types used by lesser short‐tailed bats in New Zealand, and with behaviour of many other tree‐dwelling bat species in temperate climates. Descriptive statistics of trees provide guidance to forest managers, especially those practicing silviculture, for identifying potential bat roosting habitat. Regression analyses of cavity characteristics provide insight into factors explaining the rarity of favoured cavities. Intraspecific differences in roost selection by bats should be considered when undertaking conservation management actions such as identifying trees for retention through logging cycles, or designating and designing reserves.

Dietary variation in spectacled flying foxes (Pteropus conspicillatus) of the Australian Wet Tropics

The diet of Pteropus conspicillatus, a large flying fox, was examined by collecting faeces in traps beneath daytime roost trees in four geographically distinct camps in the Wet Tropics bioregion of North-eastern Queensland, Australia. Faecal analyses revealed that P. conspicillatus utilise a broad variety of plant resources from a variety of habitats. Seed and pulp from figs (Ficus spp., Moraceae) and pollen from the family Myrtaceae were most frequently represented in the faeces from a range of both wet sclerophyll and rainforest habitats. The dietary composition of P. conspicillatus at individual camps could not be predicted by the habitats located within a typical foraging distance of each camp (20 km), and although consistent dietary changes were seen across all camps over time, each camp had a unique dietary signature indicative of feeding on a distinct subset of available vegetation. The unique diet of each camp and the variety of dietary items consumed suggest that camps may need to be managed on an individual camp-specific basis, and that P. conspicillatus are utilising a broader range of resources than would be expected if the species was a strict ‘rainforest-fruit specialist’.

Characteristics of Summer and Winter Roost Trees Used by Evening Bats (Nycticeius humeralis) in Southwestern Missouri

We radio-tracked 13 evening bats (Nycticeius humeralis) to 34 trees during the summer of 2003 and 10 evening bats to 29 trees during the winters of 2003 and 2004. We captured males in every month of the year and provide evidence suggesting that females are also year-round residents of southwestern Missouri. These captures extend the known winter range of N. humeralis at least 110 km northeast. Evening bats selected trees in late stages of decay during the summer, but during the winter they selected a higher proportion of live trees. Comparisons of summer and winter trees suggest that habitat characteristics are more important than tree characteristics in explaining variation between roosts used in the two seasons. Winter roost trees were located in areas with lower average tree height and higher densities of trees. Those attributes would likely cause problems with clutter when leaves are on the trees during summer.

Roosting and thermoregulatory behaviour of male Gould's long-eared bats, Nyctophilus gouldi: energetic benefits of thermally unstable tree roosts

Information about the thermal biology of bats in relation to their roosting behaviour is scant. I used temperature telemetry to locate roosts and record the thermoregulatory behaviour of male long-eared bats, Nyctophilus gouldi (9 g), during late spring in the Northern Tablelands of New South Wales. Bats roosted under bark and in tree cavities, where they typically experienced wide daily fluctuations in ambient temperature (Ta). On 13 out of 16 days, bats employed two torpor bouts per day, during the early morning and late afternoon, coinciding with times of low Ta. Heating of roosts during the day resulted in up to 20°C of passive re-warming before active arousal and provided high Ta around midday when bats were normothermic. By switching between torpor and normothermic thermoregulation according to the daily Ta cycle, male N. gouldi appear to gain an energetic advantage from choosing poorly insulated and often sun-exposed roosts.