Roost Switching Research Articles

Ranging Patterns and Habitat Use of a Solitary Flying Fox (Pteropus dasymallus) on Okinawa-jima Island, Japan

Most flying fox species (genus Pteropus) exhibit strong coloniality. They are highly mobile animals and commonly forage over vast areas. Only a small number of species are solitary, and their foraging and roosting patterns are not well understood. Here, we examined ranging patterns and habitat use of Orii's flying fox, Pteropus dasymallus inopinatus, a solitary fruit bat, using radiotracking from April 2002 to January 2006 on Okinawa-jima Island, Ryukyu Archipelago, Japan. The daily home range size for this species was very small (mean 52.5 ha) compared to other Pteropus species, although home range size was highly variable among individuals and seasons. The distance between a day roost and feeding trees was 621 m on average, with a maximum of 6,875 m. Day roost site shifted frequently (every 1.6 ±0.8 days) to a nearby site in the current foraging area. The distance between consecutive day roost sites was 792 m on average, with a maximum of 6,000 m. These bats favored forest habitats for roosting sites, whereas they often used residential areas as feeding sites. Our results suggest that they regularly shifted the location of their personal activity range, a small home range with roost switching, probably to track changes in food availability and to avoid local competition for food. The solitary roosting system of this species links to its flexible foraging system, which likely provides an advantage for using limited food resources on a small island, even when food is patchily distributed in urbanized habitats.

Nocturnal Activity Patterns of Lactating Silver-Haired Bats (Lasionycteris noctivagans): the Influence of Roost-Switching Behavior

A characteristic feature of forest-dwelling bats is that they regularly switch day roosts. The additional time associated with finding or assessing the availability of a new roost, moving offspring to the new roost, coordinating with other group members, and meeting any increased energetic demands that may be associated with these behaviors may influence the number and duration of feeding bouts of reproductive females. To examine the influence of roost-switching on nocturnal activity patterns we radio-tagged lactating female silver-haired bats (Lasionycteris noctivagans) and monitored them on nights when they moved to a new roost site and nights when no roost shift occurred. The typical activity pattern on a non-move night consisted of an initial long bout away from the day roost (median length: 177.4 min) followed by alternating bouts in (50.6 min) and away (57.0 min) from the roost for the rest of the night. On move nights bats reduced the length of their first absent period (82.7 min) and increased the number of trips from the roost, although neither the length of these subsequent absent periods nor the total time absent from the roosts differed from non-move nights. Similarly, total time spent in roosts did not differ between move and non-move nights, but bats made more and shorter visits on move nights. Visits to original and new roosts were not synchronous among colony members, and the length of time for individuals from the same colony to move to a new roost varied from 1 to 4 h. Our results indicate that roost switching did not influence the total time spent in or away from day roosts. Rather, bats moved between the original roost, the new roost, and foraging areas with much greater frequency on move nights.

MonasticMyzopoda: the foraging and roosting ecology of a sexually segregated Malagasy endemic bat

We studied the social organization, use of foraging habitat, roost switching and diet of the sucker-footed bat Myzopoda aurita in south-eastern Madagascar. All 138 bats caught were males, 18 of which were selected for radio-tracking. The areas individual bats used for foraging varied between 7 and 108 ha (100% minimum convex polygon). Bats foraged close the roost for the first hour after emergence, then travelled up to 1.8 km away. Compositional analysis revealed that they selected coffee plantations, degraded humid forest and wooded grassland more than any other habitats. All 133 roosts located consisted of the partially unfurled leaves of Ravenala madagascariensis and housed between nine and 51 individuals. Bats changed roosts every 1–5 days. Their diet comprised mainly of Lepidoptera and Coleoptera. No ectoparasites were observed. Myzopoda aurita is one of the few mammals endemic to Madagascar that uses disturbed patches of vegetation and is not therefore threatened by deforestation, although it may be affected by loss of roosts for building materials. The search for females continues.

Spatial and temporal patterns of roost use by western long-eared bats (Myotis evotis)

We investigated roost use by western long-eared bats (Myotis evotis), including roost fidelity, movement between roosts and the size of roosting home-ranges. We expected reproductive females, especially lactating females, to exhibit higher roost fidelity and to move shorter distances between roosts than males or nonreproductive females. Individuals generally switched roosts every 1 or 2 d. Despite their low roost fidelity, individuals occupied small roosting home-ranges (<2 ha), demonstrating fidelity to a roosting area. Roost fidelity, distances moved between roosts and roosting home-range sizes were not associated with reproductive class or reproductive period, possibly indicating that any energetic cost of roost switching is trivial in the energy budget of M. evotis, or that the advantages of roost switching outweigh any energetic cost.

Species-specific barrier effects of a motorway on the habitat use of two threatened forest-living bat species

It is generally recognized that roads can adversely affect local animal populations but little is known how roads affect bats. In particular, no study compared the response of bats that differ in foraging ecology to motorways that cut through the breeding habitat. As bats are key species in conservation, such data are urgently needed for designing management plans. Using radio-telemetry, mist netting, and mark-recapture data we investigated the effects of a motorway with heavy traffic on the habitat use of two threatened forest-living bats. We compared barbastelle bats ( Barbastella barbastellus), which forage in open space, to Bechstein’s bats ( Myotis bechsteinii), which glean prey from the vegetation. Five of six radio-tracked barbastelle bats crossed the motorway during foraging and roost switching, flying through underpasses and directly over the motorway. In contrast, only three of 34 radio-tracked Bechstein’s bats crossed the motorway during foraging, all three using an underpass. Bechstein’s bats, unlike barbastelle bats, never crossed the motorway during roost switching. Moreover, only in Bechstein’s bats individuals foraging close to the motorway had smaller foraging areas than individuals foraging further away, whereas other forest edges had no such effect. Our data show that motorways can restrict habitat accessibility for bats but the effect seems to depend on the species’ foraging ecology and wing morphology. We suggest that motorways have stronger barrier effects on bats that forage close to surfaces than on bats that forage in open space, and discuss the implications of our findings for bat conservation during road construction.

Roost Switching and Activity Patterns in the Soprano Pipistrelle,Pipistrellus pygmaeus, during Lactation

We studied roost switching and habitat selection of 16 P. pygmaeus females tagged in two nursery colonies. There were differences in overnight roosting and flying. The highest foraging activity was observed over water bodies, at forest edges and near street lamps. During each night, each female visited at least one night-roost, and five females regularly visited two roosts. On average, the females visited a roost 3.7 times per night. After parturition, the distances between night roosts and day roosts increased. The number of night roosts used declined as pups neared weaning. Five females changed day roosts after two nights. Based on the observation of flightless young in new roosts a conclusion was reached that some females transported their offspring to new roosts at night. After lactation began, some females visited roosts occupied by vocalizing males of P. pygmaeus and P. nathusii.

Cimex pipistrelli (Heteroptera, Cimicidae) and the dispersal propensity of bats: an experimental study

Previous results have shown frequent movements of crevice-dwelling bats between different shelters. Low roost fidelity of some dwelling bat species reduces the reproductive success of ectoparasites. The question of whether high densities of bat bugs (Cimex pipistrelli) represent a cost for crevice-dwelling bats (Pipistrellus pygmaeus), resulting in roost switching, has been examined. Sessions in a volary equipped with two bat boxes were carried out. One of the boxes was loaded with ectoparasites (low and high densities), the other served as a control and new roost for bats, which left the loaded box. Differences in the level of bat self-grooming, movements inside experimental boxes, and leaving the boxes between experiments with bat bugs and controls were significant. Allogrooming was observed only in few cases; therefore, the hypothesis of cooperation among individual bats in defense against bat bugs was rejected. Experiments with artificial parasitation, when bugs were added to a bat roost, showed that leaving a confined roost infested by bat bugs, i.e., roost switching, is a natural reaction of crevice-dwelling bat species, which reduces parasite load.

Influence of the microclimate of bat boxes on their occupation by the soprano pipistrelle Pipistrellus pygmaeus: possible cause of roost switching

ABSTRACT Between April and October 2003–2004, the changes in occupation of three bat boxes used by Pipistrellus pygmaeus were studied using a passive IR monitors and data loggers. Bat boxes were situated in a floodplain forest in south-eastern Moravia. Generalized additive models indicated that internal humidity described better the fluctuation in bat numbers during pregnancy and lactation than did changes in the internal temperature. Three variables (internal humidity, external temperature, and number of bats) described 87% of the variability in internal roost temperature, while the number of bats described only 29% of the variability. A negative correlation was found between the internal temperature and the number of bats roosting in a bat box the next day during pregnancy and lactation. The number of bats was also positively correlated with the internal humidity. The internal temperature of a roost with bats was biased by temperature strategies induced by the bats during particular reproductive periods...

Roost selection and roost switching of female Bechstein’s bats (Myotis bechsteinii) as a strategy of parasite avoidance

Ectoparasites of vertebrates often spend part of their life cycle in their hosts' home. Consequently, hosts should take into account the parasite infestation of a site when selecting where to live. In a field study, we investigated whether colonial female Bechstein's bats (Myotis bechsteinii) adapt their roosting behaviour to the life cycle of the bat fly Basilia nana in order to decrease their contact with infective stages of this parasite. B. nana imagoes live permanently on the bat's body but deposit puparia in the bat's roosts. The flies metamorphose independently in the roosts, but after metamorphosis emerge only in the presence of a potential host. In a field experiment, the bats preferred non-contagious to contagious day-roosts and hence were able to detect either the parasite load of roosts or some correlate with infestation, such as bat droppings. In addition, 9 years of observational data on the natural roosting behaviour of female Bechstein's bats indicate that the bats largely avoid re-occupying roosts when highly contagious puparia are likely to be present as a result of previous occupations of the roosts by the bat colony. Our results indicate that the females adapted their roosting behaviour to the age-dependent contagiousness (emergence probability) of the puparia. However, some infested roosts were re-occupied, which we assume was because these roosts provided advantages to the bats (e.g. a beneficial microclimate) that outweighed the negative effects associated with bat fly infestation. We suggest that roost selection in Bechstein's bats is the outcome of a trade-off between the costs of parasite infestation and beneficial roost qualities.

Ecological Correlates of Roost Fidelity in the Tent-Making Bat Artibeus watsoni

Roost switching is a common occurrence in bats, yet the causes and consequences of such behavior are poorly understood. In this study we explore the ecological correlates of roost fidelity in the tent-making bat Artibeus watsoni, particularly focusing on the effect of sex, reproductive status, and roost availability using a three-factor general linear model (GLM). We estimated roost fidelity of radio-tracked individuals and found that the GLM was significant (R2 = 0.72, F10,34 = 8.91, p < 0.001). Significant interaction terms were observed for relative roost availability and sex (F4,34 = 16.96, p < 0.001), and relative roost availability and reproductive status (F6,34 = 7.62, p < 0.001), indicating that variation in roost fidelity among males and females, and among individuals under different breeding conditions, depended on relative roost availability at the site where they were radio-tracked. Individuals in areas of high roost availability exhibited lower roost fidelity than those sampled in areas of lower roost availability. Females exhibited less roost fidelity than males for all roost availability categories, but the difference between males and females was only significant at high roost availability. The general pattern of decreased roost fidelity as roost availability increased was also prevalent among individuals in different breeding conditions. Additionally, satellite males exhibited higher roost fidelity than resident males in areas of low roost availability, and lactating females had higher roost fidelity than non-breeding females in areas of medium roost availability. Our study thus demonstrates that sex, reproductive status, and roost availability all affect roost fidelity in the tent-making bat A. watsoni, and also suggests that roost availability is the most important factor influencing roost fidelity in this bat, providing the first quantitative evidence that roost fidelity is correlated with roost abundance in a single species.

The sessile serotine: the influence of roost temperature on philopatry and reproductive phenology of Eptesicus serotinus (Schreber, 1774) (Mammalia: Chiroptera)

Maternity colonies of serotine bats inhabiting large roof spaces were studied at three localities in southwestern Germany and Luxembourg. Bats of all three colonies returned to the maternity roosts during the second or third week of April, and were strongly philopatric to their main roost. Roost switching occurred only rarely and for short periods. Measurements of temperature inside two roosts showed gradients according to height and aspect of the roof space with a mean roost temperature of 22°C during gestation and lactation. The availability of adequate microclimates within the roost during gestation and lactation was thought to favour roost philopatry. Females of all ages and reproductive classes inhabit the roosts throughout summer. Mean (± SD) inferred gestation length was 52 ± 6 days, and variations were not related to roost temperatures during gestation. The mean date of birth was 16th June with most births occurring within a period of 14 ± 6 days and of young first emerged from the roost 36 ± 7 days after birth. Prolonged adverse weather conditions, leading to low roost temperatures, resulted in mortality of 11–27% of preweaning young in four of the five years studied. Since immigration occurs, the number of young emerging from the roost cannot be deduced from the number of females present during gestation or lactation. Adult females and young start to disperse after the first young are weaned at the beginning of August and are last observed in October. The implications of these results for the epidemiology of European bat lyssavirus 1 are discussed.

Spatial and temporal patterns of roost use by tree‐dwelling barbastelle batsBarbastella barbastellus

We evaluated the spatial and temporal patterns of roost switching behaviour by a tree‐dwelling population of barbastelle batsBarbastella barbastellusin a beech forest of central Italy. Switching behaviour was common to both sexes and did not depend on group size. We observed both individual and group switching, the latter often involving the abandonment of a roost tree on a single night. We suggest that behaviours such as flight activity around roosts or cavity inspection by bats play a role in recruiting group mates and coordinating their occupation of another site. Bats almost never crossed mountain ridges to use roosts located beyond them, possibly because ridges are regarded as boundaries delimiting main roosting areas. The rate of switching was lowest during the middle of the lactation period, probably to minimise problems related to the transportation of non‐volant young by their mothers. Although the maintenance of social relationship among bats spread over large forest areas may partly explain the occurrence of roost switching, the persistence of this behaviour in solitary bats and the movement of entire groups best fit the hypothesis that roost switching represents a way to maintain or increase knowledge of alternative roosts.

MATERNITY ROOST SITE SELECTION OF LONG-EARED MYOTIS, MYOTIS EVOTIS

Bat conservation is hindered by a lack of geographic-specific knowledge of characteristics of roost sites used by reproductive females. We examined roost selection by reproductive female Myotis evotis (long-eared myotis) in the Channeled Scablands of northeastern Washington. We used radiotelemetry to locate 35 roosts of reproductive female Myotis evotis. Habitat variables were measured for each roost itself and at a 0.1-ha microplot and 78-ha macroplot surrounding each roost. We measured habitat variables at random 0.1-ha microplots in the vicinity of each roost and at general random 0.1-ha microplots and 78-ha macroplots. Thirty-four roosts were found in crevices in small basalt rock formations. All radiomarked bats switched roosts at least once and roost switching apparently involved the entire colony. The average number of switches was 3.3 with an average of 2 days between roost switches. The distance traveled between day roosts averaged 148.9 m. Compared to random plots, roosts were in more open, rocky habitats, closer to edge of forest stands, and relatively distant from sources of permanent water.

Roost switching, roost sharing and social cohesion: forest-dwelling big brown bats, Eptesicus fuscus, conform to the fission–fusion model

We used radiotelemetry to quantify roost switching and assess associations between members of maternity colonies of forest-dwelling big brown bats. Bats remained loyal to small roosting areas of forest within and between years and switched trees often ( X± SD=1.7±0.7 days ). For radiotagged bats from the colony in one of these areas, roost-switching frequency was positively correlated with the number of different individuals with which tagged bats shared roosts. We quantified associations between pairs of bats using a pairwise sharing index and found that bats associated more often than predicted when roost and roostmate selection were random but that all tagged bats spent at least some days roosting in different trees, apart from preferred roostmates. Our results suggest that forest-dwelling big brown bats conform to a fission–fusion roosting pattern. Roost switching in forests may reflect the maintenance of long-term social relationships between individuals from a colony that is spread among a number of different trees on a given night. In this fission–fusion scenario, switching between trees, within a local area, could serve to increase the numbers of individuals with which bats maintain associations. We contend that roosting areas in forests are analogous to spatially large roosts in caves, mines and buildings.

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.

Information transfer about roosts in female Bechstein's bats: an experimental field study.

Information transfer among group members is believed to play an important part in the evolution of coloniality in both birds and bats. Although information transfer has received much scientific interest, field studies using experiments to test the underlying hypotheses are rare. We used a field experiment to test if communally breeding female Bechstein's bats (Myotis bechsteinii) exchange information regarding novel roosts. We supplied a wild colony, comprising 17 adult females of known relatedness, with pairs of suitable and unsuitable roosts and monitored the arrival of individuals marked with transponders (PIT-tags) over 2 years. As expected with information transfer, significantly more naive females were recruited towards suitable than towards unsuitable roosts. We conclude that information transfer about roosts has two functions: (i) it generates communal knowledge of a large set of roosts; and (ii) it aids avoidance of colony fission during roost switching. Both functions seem important in Bechstein's bats, in which colonies depend on many day roosts and where colony members live together for many years.

Role of various adhesion and activation molecules in patients with coronary artery disease

Fission–fusion dynamics appear common among temperate bats where females form roost groups that change in size and composition, as females switch roosts almost daily. One hypothesis for frequent roost switching is that females move to find suitable thermal conditions as ambient conditions change. Tests of this hypothesis have, however, been conducted mostly at roosts in artificial structures where microclimate is relatively stable. The goal of our study was to determine whether roost switching and roost use by northern long-eared bats, Myotis septentrionalis, that roost in trees are related to ambient conditions. We used generalized linear fixed effects models to explore the influence of roost characteristics and changes in ambient conditions on the likelihood of roost switching. We used canonical correlation analyses to examine the relationship between ambient conditions and roost characteristics. Roost switching was indeed linked to ambient conditions together with characteristics of roosts on the previous day; the best descriptors of roost switching differed between the two geographical regions we analysed. In Nova Scotia, females were less likely to switch roosts when it rained, particularly if they were in roosts below surrounding canopy whereas they were more likely to switch roosts when they were in roosts of high decay. Females roosted in shorter trees in earlier decay classes on warm days, as well as on windy and rainy days. In Kentucky, females were more likely to switch roosts at high temperatures, particularly when they were in roosts in high decay. Females roosted in shorter, decayed trees on warm days, and in less decayed trees with small diameter on windy and rainy days. Our results suggest bats switch roosts in response to changes in ambient conditions to select suitable roosting conditions, which may explain some of the proximate factors shaping fission–fusion dynamics of bats.

Life History and Roost Switching in Six Summer Colonies of Eastern Pipistrelles in Buildings

Summer colonies of the eastern pipistrelle, Pipistrellus subflavus , in six different buildings in Indiana were studied by the owners of the buildings. Colonies generally started forming from 13 to 29 April. Size of the colony increased gradually and reached a maximum of 7 to 29 adults ( X = 15 ± 7 SD, n = 18) from 26 April to 7 June. Births occurred from 30 May to 11 July, but most young were born from 12 June to 1 July. Juveniles apparently became volant ca. 4 weeks of age and foraged with their mothers for ca. 1 week. Adults often abandoned maternity roosts soon after weaning, but young remained longer. There was considerable daily variation in the number of bats in a given colony, and sometimes the entire colony disappeared, even when flightless young were present, suggesting that each colony was using more than one roost.

Secondary Use of Aspen Cavities by Tree-Roosting Big Brown Bats

To further explore natural roost-site selection by temperate bats, we examined the use of tree roost sites by big brown bats ( Eptesicus fuscus ) in the West Block of Cypress Hills Provincial Park, Saskatchewan, an area where the number of human structures is limited. In this area, we found big brown bats roosted exclusively in cavities of trembling aspen trees ( Populus tremuloides ), despite the availability of cavities in snags of conifer trees. Most cavities had been excavated and previously used by yellow-bellied sapsuckers ( Sphyrapicus varius ). The use of aspens by sapsuckers relates to the relatively soft wood and susceptibility to heart rot of these trees, which provide ideal conditions for nesting: decayed heartwood with a firm sapwood shell. Orientation of cavity entrances was close to due south. The width of bats and the width of cavity entrances differed, suggesting that bats are not using roosts for protection from predators or exclusion of competitors. Bats showed fidelity to a particular group of roost trees because, despite roost switching, bats reunited in subsequent roost sites. During the day, temperatures in aspen cavities were approximately 50C cooler than in cavities of conifer snags. Microclimate differences, including temperature, may be why aspen cavities are selected over available cavities in conifer snags. All of the randomly selected cavities in aspen that we searched showed evidence of use by bats, which suggests roost sites for big brown bats in southwestern Saskatchewan may be a limiting resource.

Low roost-site fidelity in pallid bats: associated factors and effect on group stability

Despite potential costs of changing roost or densites, many animals frequently move between roosts or dens. Pallid bats (Antrozous pallidus) change diurnal roost sites frequently and also reportedly have a variety of cooperative social behaviors, many of which are associated with the care of developing offspring. Roost switching is likely to increase the costs of maintaining the group stability expected with social cooperation. Pallid bats roosting in rock crevices in central Oregon were studied with radiotelemetry to (1) examine characteristics of day roosts, (2) determine what ecological factors were correlated with low roost fidelity, and (3) examine the temporal stability of roosting groups of pregnant and lactating bats. Pallid bats changed roosts an average of once every 1.4 days throughout the summer. The bats exhibited seasonal shifts in roost use, occupying roosts behind thin slabs of rock in cool weather and roosts in deep rock crevices in warm weather. Roost switching was not correlated with daily variations in weather conditions or with structural characteristics of the diurnal roosts, although switching may have allowed bats to maintain familiarity with several roosts that vary in microclimate. Roost switching was positively correlated with ectoparasite load. High ectoparasite levels were correlated with lower body weights in lactating females (Fig. 3), suggesting that parasites may be costly to the bats. Roost switching may be a strategy to decrease ectoparasite loads by interrupting the reproductive cycles of those parasites that spend at least part of their life cycle on the walls of the roost. Both pregnant and lactating pallid bats frequently changed their diurnal roost location, but lactating bats tended to travel shorter distances between consecutive roosts. Lactating bats were more likely to continue to associate with particular roostmates despite changes in the location of the diurnal roost (Fig. 4) and were less likely to roost alone. Although the stability of groups of lactating bats was not absolute, evidence supported the prediction that such groups are more cohesive than are those of pregnant bats.