Roost Selection Research Articles

SELECTION OF GAMBEL OAK ROOSTS BY SOUTHWESTERN MYOTIS IN PONDEROSA PINE-DOMINATED FORESTS, NORTHERN ARIZONA

Gambel oak (Quercus gambelii) is a valuable tree species for wildlife. In Arizona, USA, it occurs at higher elevations in association with ponderosa pine (Pinus ponderosa). Southwestern myotis (Myotis auriculus) is a bat species that has been anecdotally documented as selecting Gambel oak for maternity roost sites. During summers of 1999 and 2000, we conducted a radiotelemetry study to determine whether lactating, female southwestern myotis selected Gambel oak as maternity roosts within the ponderosa pine–Gambel oak forest in northern Arizona. We located 34 maternity roosts for southwestern myotis in Gambel oak trees (14 females) and 5 roosts in ponderosa pine snags (1 female). Maternity roosts were located in live Gambel oak trees >26-cm diameter at root collar (drc) that contained cavities. We used Akaike's Information Criterion (AIC) to evaluate 4 a priori hypotheses about southwestern Myotis maternity roost selection in northern Arizona. Our top model contained parameters for roost tree height and density of potential roost trees. Roost trees were taller than randomly selected Gambel oak trees. Forest patches immediately surrounding roost trees contained a higher density of large oak trees (drc >26 cm) than around randomly selected trees. We recommend the protection of large Gambel oak trees and encourage recruitment of large Gambel oak trees from smaller size classes to ensure that roosts remain available for southwestern myotis.

Selection of diurnal roosts by red bats ( Lasiurus borealis) in an intensively managed pine forest in Mississippi

Forest managers are increasingly expected to incorporate biodiversity objectives within forest landscapes devoted to timber production. However, data on which to base management recommendations for bats within these systems are limited. Although the red bat ( Lasiurus borealis) is a widespread and common species in temperate forests of North America, little is known of its ecology within intensively managed pine ( Pinus spp.) forests of the southeastern United States. Diurnal roost sites of red bats may be limiting on industrial pine forests due to a lack of large hardwoods within managed stands. Therefore, we investigated selection of day roosts by red bats at multiple spatial scales during June–September 2000 and May–August 2001 in an intensively managed pine landscape in east-central Mississippi, USA. We captured bats using 4-tier mist nets placed over water and attached 0.47–0.54 g radiotransmitters to captured red bats ( n = 46). We located day roosts of red bats ( n = 141 roosts of 27 bats) for the life of the transmitters. Red bats roosted in 16 species of hardwood trees (70% of day roosts) and loblolly pine ( Pinus taeda; 30% of day roosts). In contrast to other studies in the southeastern United States, red bats roosted in pine trees and in midstory hardwood trees. Within thinned pine stands, red bats tended to prefer roost trees with a denser subcanopy and higher basal area as compared to random sites. Stand-level characteristics appeared more important than individual tree characteristics in choice of diurnal roosts. Except for adult males, logistic regression models of roost sites of red bats had high (≥79%) correct classification rates. Day roost site requirements of red bats may exhibit greater plasticity than previously thought. On our study area, intensive forest management appears compatible with diurnal roost needs of this species.

CHARACTERISTICS OF TREE ROOSTS OF RAFINESQUE'S BIG-EARED BAT AND SOUTHEASTERN BAT IN NORTHEASTERN LOUISIANA

We found 44 Corynorhinus rafinesquii and 1 Myotis austroriparius tree roosts during the summer of 2000 on D'Arbonne National Wildlife Refuge in northeastern Louisiana. Corynorhinus rafinesquii and M. austroriparius are species of concern throughout their range. Little information exists on tree roosts of either species. The roost trees found in our study were hollow Nyssa aquatica with triangular-shaped basal openings, and all were located within a 5-ha tupelo stand. A high density of large-diameter cavity trees and a closed canopy characterized this stand. A canal bisected the stand and provided a source of permanent water. Roost trees and non-roost trees could not be compared due to biases in sampling technique. More research directed at roost selection factors by these bats is needed to form conservation plans; however, preliminary information indicates many, large-diameter cavity trees, especially Nyssa tree species, within bottomland hardwood forests are important as tree roosts for these bats.

Influence of temperature in roost selection by Pipistrellus pygmaeus (Chiroptera): relevance for the design of bat boxes

The soprano pipistrelle ( Pipistrellus pygmaeus) is a house-dwelling bat, whose maternity colonies are often affected by exclusion from buildings in southern Europe. Bat boxes with a suitable thermal behaviour can provide alternative roosts. However, this is particularly difficult to achieve in hot climates, where boxes may overheat. We studied roost temperatures and roost thermal preferences of this bat in attics and roofs in a Mediterranean region. Roosts reached high temperatures, experienced great thermal fluctuations and had wide spatial thermal ranges. Bats preferred the warmest locations within roosts, indicating that they are a heat tolerant species. However, they avoided temperatures of 40 °C and above, suggesting that this is the upper limit of the species thermally neutral zone. The study of experimental sets of white, grey and black boxes demonstrated that the latter were the ones that most often reached the temperatures observed in roosts in buildings. They were also the ones occupied by larger numbers of bats. These results suggest that, even in hot Mediterranean climates, black boxes are the best option as alternative roosts for evicted colonies. However, on particularly hot days, bats left them, suggesting that black boxes could be improved by creating a wider thermal range.

Roost Selection and Roosting Behavior of Male Common Nighthawks

Many studies to date have documented clear energetic costs and benefits of avian roost selection. Male Common Nighthawks (Chordeiles minor) spend at least half of each day during the summer on a day-roost. Therefore selection of roost-sites likely has implications for survival and long-term fitness. Our objective was to identify characteristics of day-roosts used by male Common Nighthawks in Cypress Hills Provincial Park, Saskatchewan, Canada. We measured features of roost trees and monitored behavior of roosting birds. Nighthawks preferred trees situated on north facing slopes surrounded by trees with significantly lower canopy height compared to randomly measured trees. Roost trees were taller than random trees and occurred in less dense patches of forest. Birds always roosted parallel to branches and adopted a motionless posture. There was a non-significant trend for birds to roost on branches facing east. Birds typically roosted in a direction pointing away from the sun and away from the roost tree trunk. Roost trees emerging from the canopy may provide landmarks for birds as they search for suitable day-roosts, whereas a low tree density surrounding roost trees likely reduces flight costs associated with maneuvering. Our results suggest that roosts chosen by male nighthawks may provide selective benefits in terms of microclimate, energetics and predator avoidance, but further studies are needed to determine which is the most important.

NIGHT ROOST SELECTION DURING WINTER BY RUFFED GROUSE IN THE CENTRAL APPALACHIANS

In northern regions, ruffed grouse (Bonasa umbellus) conserve considerable energy during winter by burrowing under snow cover to roost. When conditions are unsuitable for snow burrowing grouse almost invariably roost in conifers. We studied selection of winter night roosts by ruffed grouse in western Virginia, a region where snow accumulations are rare and transient. Grouse almost always used ground roosts when snow was present even though snow was never deep enough for snow burrowing. When snow was absent grouse did not show any clear preference in roost microsite type, and were found roosting in and under deciduous and evergreen trees and shrubs, in brush piles, and in leaf litter. We hypothesize that this ambivalence to conifers was due in part to persistent accumulations of fallen oak leaves, which likely afford grouse good thermal cover and concealment. Grouse were frequently found at low elevations during daytime, but rarely roosted in bottoms. This suggests daily elevational movements, possibly to avoid cold air settling in low-lying areas during night.

Roost selection by barbastelle bats ( Barbastella barbastellus, Chiroptera: Vespertilionidae) in beech woodlands of central Italy: consequences for conservation

We investigated roost selection by Barbastella barbastellus in a mountainous area of central Italy. Twenty-five bats, mostly lactating females, were radio-tracked to 33 roost trees. Trees in unmanaged woodland were favoured as roost trees; woodland subject to limited logging was used in proportion to availability, and areas where open woodland and pasture occurred were avoided. Selection depended on tree condition (dead beech trees were preferred) and height (roost trees were taller than random ones). Cavity selection was based on cavity type, height and entrance direction: roost cavities were mainly beneath loose bark, at a greater height above ground and facing south more frequently than random cavities. Untouched areas of mature woodland should be preserved to provide roosting conditions for B. barbastellus. In logged areas, harvesting protocols should save dead and mature trees; frequent roost switching and small colony size imply that large numbers of roost trees are needed.

Thermoregulation and roost selection by reproductive female big brown bats (Eptesicus fuscus) roosting in rock crevices

A free‐ranging maternity colony of big brown bats Eptesicus fuscus roosting in rock crevices along the South Saskatchewan River in south‐eastern Alberta, Canada, was studied to understand better the discrepancy that exists in the literature regarding torpor use by reproductive female bats. Using radio‐telemetry, thermoregulatory patterns and roost microclimate were recorded for pregnant, lactating and post‐lactating females. Relative torpor use is described in several ways: the proportion of days on which torpor was used, depth, minimum body temperature, time spent in torpor, and a comprehensive torpor unit (degree‐min). Pregnant and lactating female E. fuscus used torpor to the same extent overall (degree‐min), but pregnant bats used torpor less frequently and with more time in deep torpor. Torpor was used to the greatest extent after weaning (post‐lactation). Evidence is presented that the cost:benefit ratio for deep and prolonged periods of torpor may be highest during lactation. Microclimates of rock‐crevice roosts mirrored the use of torpor throughout reproduction by bats. Lactation roosts (deeper, larger opening size) were more thermally stable and remained warmer at night compared to the shallow roosts used by pregnant and post‐lactating females. It is shown that conclusions about relative use of torpor can differ depending on the units of comparison, necessitating measurement of all aspects of torpor (depth, duration and frequency). Comprehensive measurements, individual‐based normothermic temperatures, and a definition of torpor that accounts for all energy savings, allow a more accurate depiction of patterns and facilitates inter‐study comparisons.

Conservation of bats in suburban landscapes: roost selection by Myotis yumanensis in a residential area in California

Protection of roosting habitat is essential to the conservation of bats in human-dominated landscapes. To help define bat roosting needs in suburban settings, we used radio telemetry to locate day roosts of a common North American species ( Myotis yumanensis) within a residential area in California. Between June and August 2000, we tracked 16 bats to 20 roosts in two buildings and 18 trees. We used multiple logistic regression to assess roost selectivity at multiple spatial scales. Of 15 tree, plot, and site characteristics considered, only three helped distinguish roosts from random comparisons: tree diameter, distance to water, and forest cover. Myotis yumanensis preferred large trees (mean diameter 115 cm), and roosted only in the five species of largest mean diameter ( Sequoia sempervirens, Pseudotsuga menziesii, Quercus agrifolia, Quercus lobata, and Acer macrophyllum). At the site level, these bats selected roosts that were close to water and had substantial forest cover in the surrounding 100-m radius. Unlike other North American bats, they often roosted in live trees (89% live). Relatively high roost fidelity (mean 4.8 days) and large travel distances between consecutive roosts (mean 1130 m) and between capture sites and roosts (mean 2007 m) may indicate a greater degree of roost limitation at this site versus other research sites. We recommend the preservation of large trees and forested parkland, particularly along stream corridors, to help maintain bat populations in urbanizing landscapes.

Habitat use, diet and roost selection by the Big Brown Bat (Eptesicus fuscus) in North America: a case for conserving an abundant species

ABSTRACTInsectivorous bats are integral components of terrestrial ecosystems. Despite this, a growing number of factors causing world‐wide declines in bat populations have been identified. Relatively abundant species are important for bat conservation because of their role in ecosystems and the research opportunities they offer. In addition, species that have been well‐studied present unique opportunities to synthesize information and highlight important areas of focus for conservation and research. This paper focuses on a well‐studied abundant bat, Eptesicus fuscus. I review the relevant literature on habitat use, diet and roost selection by E. fuscus in North America, and highlight important areas of conservation and research for this species, including the effects of roost disturbance, control of economically important insect pests, exposure to pesticides, long‐term monitoring of populations, and the potential consequences of expanding populations. These issues have broad implications for other species and can be used to focus future research and conservation efforts.

Selection of roost sites by the lesser long‐eared bat (Nyctophilus geoffroyi) and Gould's wattled bat (Chalinolobus gouldii) in south‐eastern Australia

AbstractPhysical characteristics of roost sites used by the lesser long‐eared bat Nyctophilus geoffroyi and Gould's wattled bat Chalinolobus gouldii were investigated in a farmland–remnant vegetation mosaic and adjacent forested floodplain in south‐eastern Australia. A total of 45 individuals of N. geoffroyi and 27 C. gouldii were fitted with radio‐transmitters, resulting in the location of 139 and 89 roosts, respectively. Male N. geoffroyi roosted in trees, fallen and decayed timber and artificial structures. These roosts were low to the ground, mainly under bark and in cracks in timber. Roosts of female N. geoffroyi were located higher above ground, and all within trees. Maternity roosts were predominantly located in large dead trees, approximately twice the diameter of roost trees used by females outside the breeding season. No maternity roosts were found under bark, despite half the roosts used by non‐breeding females being located in these situations. Both sexes roosted primarily in dead timber and used cavities where the narrowest dimension of the entrance was 2.5 cm. Most roosts of C. gouldii were in dead spouts on large, live river red gum Eucalyptus camaldulensis trees. Intraspecific differences in roost characteristics were less pronounced for this species. Despite access to the same roosting opportunities, there were marked differences in roost selection between N. geoffroyi and C. gouldii. Both species favoured large diameter trees, but differed significantly for all other measured variables: type of roost structure, condition of roost tree (live or dead), height of roost tree, height of roost, and entrance dimensions. Although these species are among the most widespread bats in Australia and are often considered to be habitat ‘generalists’, both displayed a high level of discrimination in the roosts used. Clearly, roosting requirements are a complex and important issue in the conservation of even the most common species of bats.

Roosting behaviour and roost selection of female big brown bats (Eptesicus fuscus) roosting in rock crevices in southeastern Alberta

We studied big brown bats (Eptesicus fuscus) roosting in rock crevices along the South Saskatchewan River in southeastern Alberta. We documented roosting behaviour and roost selection. During pregnancy and lactation, individuals aggregated as several small groups or one large group (maternity colony). Postlactating females roosted alone more frequently. During postlactation, individuals periodically returned to roost with a group dominated by pups, between periods of roosting alone. We identified 72 roosts used by members of the colony. Adult females switched roosts frequently and few roosts (24%) were reused. During pregnancy and lactation, the colony roosted in a 1.25-km length of the river valley on the northwest side of the river. With the onset of postlactation, females began roosting on both sides of the river and within a longer section of the river valley, and roosts faced in a more southerly direction. Crevices selected as roosts were more vertical in orientation, were farther from level ground above, and had openings that were smaller than those randomly available. Roosts used during pregnancy, lactation, and postlactation differed in physical attributes; lactation roosts were deeper and had larger openings. Selection of crevices with particular attributes suggested that selection was based on microclimate and avoidance of predation.

Quality of cavity microclimate as a factor influencing selection of maternity roosts by a tree‐dwelling bat, Chalinolobus tuberculatus, in New Zealand

Summary Cavity quality is important for the productivity and survival of many species of tree‐dwelling wildlife. Intensive land management practices, such as logging and agriculture, frequently reduce cavity availability and potentially affect the long‐term viability of populations. The New Zealand long‐tailed bat Chalinolobus tuberculatus selects roosts in small knot‐hole cavities with specific structural properties relative to available cavities. They also change roosts daily among a large pool of different roosts. Such behaviour is likely to make C. tuberculatus vulnerable to human‐induced deterioration in roosting habitat. This study represents a case study of the degree of sophistication sometimes required to assess availability and quality of roost sites, by testing whether roosts selected by C. tuberculatus also have specific microclimates. Selection for microclimate was demonstrated by comparing temperature and humidity inside unoccupied maternity roosts with available, apparently unused, knot‐hole cavities, large trunk‐hollows and ambient conditions. Compared with ambient conditions, roost and available knot‐hole cavities had stable microclimates displaying only small ranges in temperature and humidity. Temperature inside cavities was lower than ambient temperature in the day and was warmer (and peaked) at night. Humidity in cavities was constantly high. Mean temperatures within trunk‐hollows (not known to be used by C. tuberculatus) were cooler than mean ambient and roost temperatures, and temperature ranges in hollows were large and fluctuated similarly to ambient temperatures. Compared with available cavities and hollows, roost cavities had higher minimum temperatures, and maximum temperatures occurred significantly later in the day and continued for significantly longer. Humidity ranges were less and high humidity was maintained for longer. The results suggest that C. tuberculatus selects maternity roost sites with microclimatic conditions that are likely to accrue substantial energetic benefits. Predicted energy savings for adult bats using roost cavities compared with available knot‐holes were 1·1–3·3%, and compared with hollows 3·4–7·3%. Greater energy savings would occur at night and benefit non‐volant young. In order to evaluate adequately and mitigate the full impacts of land‐use practices, there is a need for wider tests to provide direct evidence of interactions between habitat management, cavity provision and survival of cavity‐dependent wildlife.

DAY-ROOST SELECTION BY RAFINESQUE'S BIG-EARED BATS (CORYNORHINUS RAFINESQUII) IN LOUISIANA FORESTS

Availability of bridge roosts is a poorly understood but possibly important component underlying abundance and distribution of the potentially threatened bat Corynorhinus rafinesquii. We analyzed structural characteristics and surrounding habitat of 81 bridges in west-central Louisiana forests to determine which attributes of bridges influenced the selection of roosts by C. rafinesquii. Type of support structure under bridges, material with which bridges were built, proportion of surrounding habitat composed of mature deciduous forest, and road surface of bridges were significantly associated with selection of roost sites. On average, bats tagged with radiotransmitters roosted under bridges 50% of the time and in black gum trees (Nyssa sylvatica) 50% of the time. Preservation of bridges with beam supports and conservation of mature deciduous forest are likely to be important for maintaining populations of C. rafinesquii.

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

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

Roost selection by noctules (Nyctalus noctula) and Daubenton's bats (Myotis daubentonii)

Roost selection by tree roosting noctules Nyctalus noctula and Daubenton's bats Myotis daubentonii was determined by comparing roost characteristics with the characteristics of randomly chosen tree cavities in the area. The following parameters were determined for 81 noctule roosts and 27 Daubenton's bat roosts: tree species, type of cavity (woodpecker or natural), entrance height, compass direction of entrance and distance to the edge of the wood. Roost choice of both bat species was similar except that Daubenton's bats used woodpecker cavities less than noctules. Both bat species were selective in their roost choice. Daubenton's bats preferred oaks over beeches, and noctules preferred woodpecker cavities over natural cavities, indicating dependence on woodpeckers. Both bat species preferred to roost close to the edge of the wood. Roosting close to the edge of the wood may reduce commuting flight costs for both species or may be preferable for thermoregulatory reasons.

Roosts used by the golden‐tipped bat Kerivoula papuensis (Chiroptera: Vespertilionidae)

AbstractUse of roosts by the golden‐tipped bat Kerivoula papuensis was investigated principally in the Richmond Range National Park, north‐eastern New South Wales and Mt Baldy State Forest in north‐eastern Queensland, Australia. Roosts were located primarily using radiotelemetry; although others were found by light tagging, visual location and nest searching techniques. In the main study site in the Richmond Range a total of 54 K. papuensis diurnal roosts were located, 96.5% occurring in the suspended nests of the yellow‐throated scrubwren Sericornis citreogularis (Pardalotidae) (93%) and the brown gerygone Gerygone mouki (Pardalotidae) (3.5%). At Mt Baldy, K. papuensis displayed greater variation in day roost selection, although 73% were in S. citreogularis nests. In both sites, day roosts were confined to the lower stratum of rainforest with a small proportion in eucalypt tall open forest with a rainforest subcanopy. Diurnal roosts were located at distances varying from 20 to 1200 m to the nearest major vegetation ecotone, ranging from along watercourses upslope to ridgelines. Diurnal roosts were predominantly occupied by single bats, with a maximum group size of eight individuals. All roosts in hanging nests were modified by the presence of a basal hole. Strong circumstantial evidence was provided that K. papuensis modified these roost structures in a manner allied to tent‐making bats. A single maternity roost was located in the hollow of a rainforest canopy tree, Flindersia australis (Rutaceae).

Selection of Day Roosts by Red Bats in Mixed Mesophytic Forests

Limited information exists on the choice of day roosts by red bats (Lasiurus borealis) in mature deciduous forests. We radiotracked 10 adult female and 4 adult male red hats as they used 44 day roosts in nived mesophytic forests in castern Kentucky during May through August 1996-97. On average (x ± SE). bats roosted 16.5 ± 0.3 to above ground in the outer foliage of the canopy of 13 different species of hardwood trees: no conifer or snag was used as a day roost. Roost trees were dominant and codominant trees averaging 10.5 1.9 cur dblt. Most roost trees 77.3% were on ridge tops of upland forests. Each hat used an average of 11 roost trees and switched roost trees every 2.3 days in an area <40 m 2 . Day roosts were 277 ± 30 m from lorest edge. with no roost located < 50 m from any edge. These data indicate that choice of day roosts In red bats inhabiting tracts of mature contiguous forest differs from those in fragmented habitats.

Habitat selection by the rare golden-tipped bat Kerivoula papuensis.

Habitat selection by the golden-tipped bat Kerivoula papuensis was described using presence/absence data from 144 harp trapping sites between Cooktown in north-eastern Queensland and Bulahdelah in central-eastern New South Wales. Logistic regression was used to identify structural, topographic and other attributes of sites associated with the presence of K. papuensis. Occupied habitat was characterised by an abundance of vine drapes, the presence of the yellow-throated scrubwren Sericornis citreogularis, close spacing between stream channels, multiple tree layers, high relief and slope characteristics, westerly aspect, higher elevations, low abundance of large tree epiphytes and proximity to the nearest forest ecotone. However, aspects of habitat selection are poorly known, such as maternity roost selection and foraging habitat by the species. Further study is required to fully understand the habitat requirements of this species.

Roost Selection, Population Size and Habitat Use by a Colony of Rafinesque's Big-eared Bats (Corynorhinus rafinesquii)

Abstract Rafinesque's big-eared bat (Corynorhinus rafinesquii) is a species of concern throughout much of its range, with limited information available on the life history of this rare bat. We tracked patterns of population size, measured roost temperatures and used radiotelemetry to locate foraging areas of C. rafinesquii inhabiting a sandstone cave, which these bats used as both a hibernaculum and a maternity site. Counts of hibernating C. rafinesquii ranged from 14–49, with summer colony size reaching a maximum of 118 bats. Bats roosted in different rooms of the cave in winter and summer. Temperatures in a room used in winter were consistently cooler and less stable than temperatures in the room used as the maternity site. Size of foraging areas ranged from 61.6–225.3 ha, and distance of foraging areas from the roost varied from 0.12–1.22 km. We detected no bat >2.5 km from the roost of capture. Bats foraged along ridgelines supporting upland oak-hickory forest.