Roosting ecology of Stenodermatinae bats (Phyllostomidae): evolution of foliage roosting and correlated phenotypes

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Roost and hunting site fidelity of female and juvenile Daubenton's bat Myotis daubentonii (Kuhl, 1817) (Chiroptera: Vespertilionidae)

We investigated roosting and hunting site fidelity of Daubenton's bats Myotis daubentonii (Kuhl, 1817) in the Forêt de Soignes, an old-stand forest dominated by 150–200-year-old beeches, during the summers of 2003 and 2004. Roosting behaviour and hunting activity over ponds of adult females and juveniles were monitored using radio-telemetry. Eighteen roosts were located, all in natural cavities. The bats occupied a limited number of trees located in a specific and small roosting area. This roost aggregation was not linked to the distribution of hollow trees. Furthermore, whereas all 11 ponds in the study area were exploited by Daubenton's bats, monitored individuals were limited to two ponds to which they showed high fidelity. These two ponds were not the closest to the roosting area. Overall, these results show that at least for the time we conducted our experiment, female and juvenile Daubenton's bats are highly faithful to specific roosting and hunting grounds.     

Roost use by long-tailed bats in South Canterbury: examining predictions of roost-site selection in a highly fragmented landscape

We studied the roosting ecology of the long-tailed bat (Chalinolobus tuberculatus) during the springautumn months from 1998–2002 at Hanging Rock in the highly fragmented landscape of South Canterbury, South Island, New Zealand. We compared the structural characteristics and microclimates of roost sites used by communally and solitary roosting bats with those of randomly available sites, and roosts of C. tuberculatus occupying unmodified Nothofagus forest in the Eglinton Valley, Fiordland. Roosting group sizes and roost residency times were also compared. We followed forty radio-tagged bats to 94 roosts (20% in limestone crevices, 80% in trees) at Hanging Rock. Roosts were occupied for an average of 1 day and 86% were only used once during the study period. Colony size averaged 9.8 ± 1.1 bats (range 2–38) and colonies were dominated by breeding females and young. Indigenous forest, shrubland remnants and riparian zones were preferred roosting habitats. Communally roosting bats selected roosts in split trunks of some of the largest trees available. Selection of the largest available trees as roost sites is similar to behaviour of bat species occupying unmodified forested habitats. Temperatures inside 12 maternity roosts measured during the lactation period were variable. Five roosts were well insulated from ambient conditions and internal temperatures were stable, whereas the temperatures inside seven roosts fluctuated in parallel with ambient temperature. Tree cavities used by bats at Hanging Rock were significantly nearer ground level, had larger entrance dimensions, were less well insulated, and were occupied by fewer bats than roosts in the Eglinton Valley. These characteristics appear to expose their occupants to unstable microclimates and to a higher risk of threats such as predation. We suggest that roosts at Hanging Rock are of a lower quality than those in the Eglinton Valley, and that roost quality may be one of the contributory factors in the differential reproductive fitness observed in the two bat populations. The value of introduced willows (especially Salix fragilis) as bat roosts should be acknowledged. We recommend six conservation measures to mitigate negative effects of deterioration of roosting habitat: protection and enhancement of the quality of existing roosts, replanting within roosting habitat, provision of high quality artificial roosts, predator control, and education of landowners and statutory bodies.     

Roosting behaviour is related to reproductive strategy in brood parasitic cowbirds

Shiny Cowbirds Molothrus bonariensis and Screaming Cowbirds Molothrus rufoaxillaris are closely related brood parasites but the former is socially polygynous or promiscuous and an extreme host generalist, whereas the latter is socially monogamous and parasitizes almost exclusively one host. Females of both species lay in relative darkness, before dawn, relying for host nest location on previous days’ prospecting activity, or possibly on following better‐informed roost associates. We studied the temporal and spatial patterns of roosting behaviour in these species to test the hypothesis that roosting behaviour of cowbirds is related to their breeding strategy (brood parasitism) and reflects differences in strategies between species. We recorded fidelity to a roost, location fidelity within a roost, inter‐individual spatial associations and timing of roost departures and parasitic events, using tagged individuals. Female Shiny Cowbirds and both sexes of Screaming Cowbirds showed marked fidelity in roosting location, and roost departures occurred both during and after the known time window for parasitism, with earlier departures probably corresponding to laying days. Screaming Cowbird females and males that were trapped together and showed high levels of association during the day, also showed high levels of association in the roost. We describe the spatial and temporal patterns of a relatively poorly known aspect of avian ecology in general and the behaviour of brood parasites in particular.     

Roosting Behavior of Colonial and Solitary Flying Foxes in American Samoa (Chiroptera: Pteropodidae)1

We examined characteristics of roosting sites utilized by two flying fox species (Pteropus tonganus and P. samoensis) in American Samoa. The colonial roosting sites of P. tonganus were observed over a ten‐year period, including two years when severe hurricanes devastated bat populations and destroyed roost trees. Prior to the hurricanes, roosts were located on cliff faces above the ocean or steep mountainsides, locations that were either inaccessible to people or in protected areas where hunting was not allowed. In the years immediately following the hurricanes, P. tonganus colonies split into smaller groups that moved frequently to different locations. Four years after the second hurricane, colonies had coalesced and returned to many of the traditional roosting sites used before the hurricanes. Common tree species in upland and coastal forest were selected as roosts. The isolated locations selected for P. tonganus roosts were apparently the result of hunting pressure on the colonies. The solitary roosts of P. samoensis were observed during 29 months. Roosting bats were well concealed and hard to detect within the forest; even bats on exposed branches were cryptic. Mature primary forest was favored as roosting habitat. Individual bats used specific branches or trees as roosts and returned to them for up to 29 months. Unlike P. tonganus, people did not alarm roosting P. samoensis easily and some roosts were located near houses and along roads.     

Comparative Roosting Ecology of Cynopterus (Chiroptera: Pteropodidae) Fruit Bats in Peninsular Malaysia1

Although the use of modified roosts has been reported in more than 20 species of bats in the tropics, comparative studies of the roosting ecology of congeneric tent‐roosting species are notably lacking. In the Paleotropics, this unique behavior has been described in two species belonging to the genus, Cynopterus: C. sphinx and C. brachyotis. However, it is not known whether tent roosting is an essential component of their roosting ecology, or whether the behavior is found in other members of the genus. In this study we characterize the roosting ecology of four sympatric species of Cynopterus in peninsular Malaysia and use these data to address two main questions. (1) Do all four species use modified roosts and, in those that do, is tent‐roosting obligate or opportunistic? (2) Do species pairs overlap in roost preferences and roosting habitat and, if so, is there evidence for interspecific interactions in relation to these resources? We radio‐tracked bats at two floristically distinct sites and located a total of 249 roosts. Interspecific roost niche overlap was minimal at both sites and we found no evidence for interspecific competition for roost resources at the local level. Species differences in roosting ecology were defined primarily by spatial separation of roosting habitats and secondarily by within‐habitat differences in roost selection. Importantly, we found that although periodic use of modified roosts was a characteristic shared by all four species, most roosts were unmodified, indicating that tent roosting is a facultative behavior in Malaysian Cynopterus.     

Communal roosting in the Magpie (Pica pica)

Summary Why does MagpiesPica pica roost communally rather than solitarily in winter? Most roosts were situated in deciduous trees near water, and they held relatively small numbers of birds. All Magpies roosted communally in winter. Strong winds reduced the height of roost perches, and roosting in leeward conditions increased. Less time was spent at the roost before and following roosting in winter when compared with the autumn and the spring situations. Magpies from high quality territories arrived late in the evening and left early in the morning. Foraging activity increased at the roost as day-length decreased, whereas flying remained constant. Sexual and aggressive behaviour were common in spring. Juveniles were sub-ordinate at the roost. Communal gathering was common at the roost. Several activities occurred frequently either at the pre-roost or at the roost, but aggressive and sexual behaviour had a spatial distribution as expected from the number of birdhours spent in the two sites. Roosting ceased following initiation of nesting activity, but early nesters attended the roost longer than late nesters following start of nest building. Start of breeding was not synchronized within roosts. Predation was rare at the roost and elsewhere in the study area. Roosting seems not to be due to information centre effects, predator avoidance, favourable micro-climate, lack of roost sites, or synchronization of breeding activities. Magpies may monitor the quality of their neighbours including their mating status at the roost. Communal roosting of corvid species seems to be related primarily to the distribution and the abundance of food, species with an unpredictable food supply roosting communally.

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Gemeinsames Übernachten bei der ElsterPica pica

Zusammenfassung Warum ziehen Elstern Gemeinschaftsschlafplätze der Einzelübernachtung vor? Viele Übernachtungsplätze liegen in Laubbäumen am Wasser und werden meist nur von relativ wenigen Individuen benutzt. Im Winter übernachteten jedoch alle Elstern in größeren Scharen (Abb. 1). Starker Wind verringert die Höhe der Sitzplätze und begünstigt leewärts gelegene. Vor und nach dem Übernachten waren die Elstern im Winter weniger lange Zeit answesend als im Frühjahr und Herbst (Abb. 6). Elstern aus Revieren hoher Qualität kamen abends später und flogen morgens früher wieder ab (Abb. 7, 8). Nahrungssuche am Übernachtungsplatz nahm mit abnehmender Tageslänge zu; Flugaktivität blieb konstant. Im Frühjahr waren Anzeichen von Aggressivität und Sexualverhalten häufig. Juv. nahmen an Übernachtungsplätzen niedrigere Rangstellungen ein. Schwarmbildung war häufig. Verschiedene Aktivitäten waren häufig entweder vor oder am Übernachtungsplatz festzustellen, doch Aggressiv- und Sexualverhalten konzentrieren sich meistens auf Plätze außerhalb. Nach Beginn des Nestbaus wurde der gemeinsame Übernachtungsplatz nicht mehr aufgesucht (Abb. 12), doch blieben Frühbrüter relativ länger als Spätbrüter gemessen am Stand des Brutgeschäfts. Innerhalb einer Übernachtungsgesellschaft verlief der Beginn des Nestbaus nicht synchron. Der Feinddruck am Schlafplatz wie im übrigen Untersuchungsgebiet war sehr gering. Gemeinsames Übernachten scheint keine Bedeutung als Informationszentrum oder für Verringerung der Feindeinwirkung zu besitzen, noch ist es wegen günstigen Mikroklimas, des Fehlens geeigneter Übernachtungsplätze oder als Mittel der Synchronisation des Brutgeschäftes erklärbar. Elstern prüfen vielleicht die Qalität ihrer Nachbarn und ob sie verpaart sind. Gemeinsames Übernachten scheint bei Corviden in erster Linie mit der Verteilung und Menge der Nahrung zusammenzuhängen: Arten mit einem nicht vorhersagbaren Nahrungsangebot übernachten gemeinsam.

     

Roosting behavior of a Neotropical migrant songbird, the northern waterthrush Seiurus noveboracensis, during the non-breeding season

Several species of Nearctic-Neotropical migratory songbirds appear to form roosting aggregations while on their wintering grounds but little is understood about the ecology of this behavior. We studied roosting behavior and patterns of roost habitat selection in the northern waterthrush Seiurus noveboracensis , during three winter years (2002–2004) in Puerto Rico using radio telemetry. Overall, red mangrove was selected for roosting disproportionately to its availability. Regardless of diurnal habitat used, 87% (n=86) of northern waterthrush selected dense stands of coastal red mangrove for roost sites. Individuals traveled up to 2 km to access roost sites in this habitat on a daily basis. The majority (8 of 14) of individuals roosted alone, while others roosted in loose aggregations near communal roosts of gray kingbirds Tyrannus dominicensis . Patterns of roost site selection did not vary by sex. Individuals showing aggressive response to playback during the day, however, selected roost sites significantly closer to the coast. Several additional migratory and resident bird species also used red mangrove for night-time roosting habitat. Red mangrove may be a critical nocturnal roosting habitat for bird populations that live in proximity to coastal areas in the Neotropics. The benefits of nocturnal roosting behavior as well as why individuals appear to select red mangrove remain poorly understood.     

Roosting and Foraging Social Structure of the Endangered Indiana Bat (Myotis sodalis)

Social dynamics are an important but poorly understood aspect of bat ecology. Herein we use a combination of graph theoretic and spatial approaches to describe the roost and social network characteristics and foraging associations of an Indiana bat (Myotis sodalis) maternity colony in an agricultural landscape in Ohio, USA. We tracked 46 bats to 50 roosts (423 total relocations) and collected 2,306 foraging locations for 40 bats during the summers of 2009 and 2010. We found the colony roosting network was highly centralized in both years and that roost and social networks differed significantly from random networks. Roost and social network structure also differed substantially between years. Social network structure appeared to be unrelated to segregation of roosts between age classes. For bats whose individual foraging ranges were calculated, many shared foraging space with at least one other bat. Compared across all possible bat dyads, 47% and 43% of the dyads showed more than expected overlap of foraging areas in 2009 and 2010 respectively. Colony roosting area differed between years, but the roosting area centroid shifted only 332 m. In contrast, whole colony foraging area use was similar between years. Random roost removal simulations suggest that Indiana bat colonies may be robust to loss of a limited number of roosts but may respond differently from year to year. Our study emphasizes the utility of graphic theoretic and spatial approaches for examining the sociality and roosting behavior of bats. Detailed knowledge of the relationships between social and spatial aspects of bat ecology could greatly increase conservation effectiveness by allowing more structured approaches to roost and habitat retention for tree-roosting, socially-aggregating bat species.     

Using infrared thermography to detect night‐roosting birds

Most birds sleep while roosting at night. Although a widespread behavior, few investigators have studied the nocturnal roosting behavior of birds. Studies conducted to date have either focused on species that roost communally or used radio‐telemetry to locate sleeping individuals of a few focal species. Portable thermal cameras capable of detecting infrared (IR) heat signals may provide a more efficient and less invasive means of detecting nocturnal‐roosting endotherms such as birds. Our objective was to assess the efficacy of using thermal cameras to detect roosting birds in a woodland bird community in southeastern Australia. To better understand the limitations of using thermography to detect roosting birds, paired bird surveys were conducted along 44 transects from May to September 2016 using both traditional survey techniques during the day and surveys with a thermal camera at night. We detected 195 birds representing 21 species at nocturnal roosts using IR thermography, with the detection rate of birds during nocturnal surveys approximately one‐third (29.1%) that during diurnal surveys. Detection rates during nocturnal surveys declined more steeply with distance from observers than for diurnal surveys. Detection rates were significantly higher during diurnal surveys for 14 species of woodland birds, but did not differ between diurnal and nocturnal surveys for eight other species. Roost height, roost visibility, bird mass, and cluster size (i.e., two or more birds in physical contact) did not differ between species categorized as having high or low detectability during nocturnal surveys. Variability among species in nocturnal‐detectability could not be attributed to roost‐site visibility, roost height, or bird size. Positive detection biases associated with diurnal behavior, such as movement and vocalizations, and limitations of current IR technology, e.g., low resolution, likely contributed to overall lower detection rates during nocturnal surveys. However, our results suggest that infrared thermography can be an effective and useful technique for detecting roosting birds and studying roosting behavior, as well as for population monitoring under certain conditions.     

Hunting Activity Effects on Roost Selection by Male Wild Turkeys

Roosting is an important component of wild turkey (Meleagris gallopavo; turkey) ecology as roosts provide security from predators and inclement weather. Males call (gobble) from roosts during the reproductive season, and roost locations are important for maximizing access to females and transmission of calls across the landscape, while also minimizing predation risk. Spring hunting of male turkeys occurs during the reproductive season, and hunting activity influences male behaviors and calling. Because roost sites are important for wild turkey ecology, we evaluated roost site selection and fidelity of male turkeys relative to land cover types, vegetative characteristics, and the presence of hunting activity during 2017–2018 in Georgia, USA. Prior to onset of hunting, males selected roosts nearest to hardwood and pine (Pinus spp.) forests. Roost site fidelity was low and distances between roosts were large. After onset of hunting, males selected pine forests less and exhibited greater plasticity in roost selection while fidelity remained minimal, suggesting that males may have altered selection to mitigate risk from hunting while maintaining the strategy of moving about their ranges and roosting at different sites on consecutive nights. Future research should examine potential effects of hunting-induced shifts in resource selection on other aspects of male turkey behavior and ecology. © 2019 The Wildlife Society.     

Mechanisms for the formation and maintenance of traditional night roost aggregations in a territorial damselfly

Communal roosting has been studied extensively in birds, but the mechanisms and functions of this taxonomically widespread behaviour pattern remain poorly understood. We studied the roosting behaviour of rubyspot damselflies, Hetaerina americana, in relation to sex and territorial status, and conducted field experiments to test for specific mechanisms of roost formation and maintenance. Both sexes tended to return close to their previous night's roost, but only males were significantly more roost site faithful than chance expectations based on individual day ranges. Males were more roost site faithful when they held mating territories. After acquiring a territory, males usually began roosting closer to the territory after a delay of a few days. Roosts were not located at sites that reduced the daily commuting distance between hunting areas and territories; males generally hunted closer to their territories than to their roosts. In field experiments, sites 'seeded' with synthetic models of male rubyspots attracted more recruits than vacant control sites and control sites seeded with nonrubyspot (clear-winged) damselfly models. Sites seeded repeatedly with rubyspot models often remained popular for roosting after the models were removed, suggesting that the models established new traditional roosts. These results indicate that conspecific attraction and individual spatial memory together may be sufficient to explain, at a proximate level, the traditional night roost aggregations of this species. We discuss these results in relation to functional hypotheses for roost site choice and fidelity. Copyright 2000 The Association for the Study of Animal Behaviour.     

Social calls used by a leaf-roosting bat to signal location

Social calls in bats have many functions, including mate attraction and maintaining contact during flight. Research suggests that social calls may also be used to transfer information about roosts, but no studies have yet demonstrated that calls are used to actively attract conspecifics to roosting locations. We document the social calls used by Spix''s disc-winged bat (Thyroptera tricolor) to actively recruit group members to roosts. In acoustic trials, we recorded two sets of calls; one from flying individuals termed ‘inquiry calls’, and another from roosting bats termed ‘response calls’. Inquiry calls were emitted by flying bats immediately upon release, and quickly (i.e. 178 ms) elicited production of response calls from roosting individuals. Most flying bats entered the roost when roosting individuals responded, while few bats entered the roost in the absence of a response. We argue that information transfer concerning roost location may facilitate sociality in T. tricolor, given the ephemeral nature of roosting structures used by this species.     

Sociality influences thermoregulation and roost switching in a forest bat using ephemeral roosts

In summer, many temperate bat species use daytime torpor, but breeding females do so less to avoid interferences with reproduction. In forest‐roosting bats, deep tree cavities buffer roost microclimate from abrupt temperature oscillations and facilitate thermoregulation. Forest bats also switch roosts frequently, so thermally suitable cavities may be limiting. We tested how barbastelle bats (Barbastella barbastellus), often roosting beneath flaking bark in snags, may thermoregulate successfully despite the unstable microclimate of their preferred cavities. We assessed thermoregulation patterns of bats roosting in trees in a beech forest of central Italy. Although all bats used torpor, females were more often normothermic. Cavities were poorly insulated, but social thermoregulation probably overcomes this problem. A model incorporating the presence of roost mates and group size explained thermoregulation patterns better than others based, respectively, on the location and structural characteristics of tree roosts and cavities, weather, or sex, reproductive or body condition. Homeothermy was recorded for all subjects, including nonreproductive females: This probably ensures availability of a warm roosting environment for nonvolant juveniles. Homeothermy may also represent a lifesaver for bats roosting beneath loose bark, very exposed to predators, because homeothermic bats may react quickly in case of emergency. We also found that barbastelle bats maintain group cohesion when switching roosts: This may accelerate roost occupation at the end of a night, quickly securing a stable microclimate in the newly occupied cavity. Overall, both thermoregulation and roost‐switching patterns were satisfactorily explained as adaptations to a structurally and thermally labile roosting environment.     

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 (). 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.     

A genetic analysis of group movement in an isolated population of tree-roosting bats

Group fission is an important dispersal mechanism for philopatric adults. In Cypress Hills Interprovincial Park, Saskatchewan, tree-roosting big brown bats (Eptesicus fuscus) exhibit fission-fusion roosting behaviour. During 2004-2007, the majority of females previously resident to roosting area 1 (RA1) moved to a new roosting area (RA4). We examined how genetic relationships, inferred from data for microsatellite loci and mitochondrial DNA, influenced new roost area (RA) selection during 2006 when colony members were split between the RAs. We found that females who moved to RA4 had higher average relatedness than those that remained in RA1. We found that nearly all females belonging to matrilines with high average relatedness moved to RA4 while females from matrilines with low average relatedness were split between the two RAs. These results suggest that closely related maternal kin preferentially move to new RAs. However, daily roosting preferences within a RA are not based on genetic relationships probably because daily roosting associations between kin and non-kin are used to ensure adequate roost group size. Studying the effects of kinship on the fission and movements of groups not only enhances our understanding of social behaviour and population genetics but also informs conservation decisions.     

External temperature and distance from nearest entrance influence microclimates of cave and culvert‐roosting tri‐colored bats (Perimyotis subflavus)

Many North American bat species hibernate in both natural and artificial roosts. Although hibernacula can have high internal climate stability, they still retain spatial variability in their thermal regimes, resulting in various “microclimates” throughout the roost that differ in their characteristics (e.g., temperature and air moisture). These microclimate components can be influenced by factors such as the number of entrances, the depth of the roost, and distance to the nearest entrance of the roost. Tri‐colored bats are commonly found roosting in caves in winter, but they can also be found roosting in large numbers in culverts, providing the unique opportunity to investigate factors influencing microclimates of bats in both natural and artificial roost sites. As tri‐colored bats are currently under consideration for federal listing, information of this type could be useful in aiding in the conservation and management of this species through a better understanding of what factors affect the microclimate near roosting bats. We collected data on microclimate temperature and microclimate actual water vapor pressure (AWVP) from a total of 760 overwintering tri‐colored bats at 18 caves and 44 culverts. Using linear mixed models analysis, we found that variation in bat microclimate temperatures was best explained by external temperature and distance from nearest entrance in both caves and culverts. External temperature had a greater influence on microclimate temperatures in culverts than caves. We found that variation in microclimate AWVP was best explained by external temperature, distance from nearest entrance, and proportion from entrance (proportion of the total length of the roost from the nearest entrance) in culvert‐roosting bats. Variation in microclimate AWVP was best explained by external temperature and proportion from entrance in cave‐roosting bats. Our results suggest that bat microclimate temperature and AWVP are influenced by similar factors in both artificial and natural roosts, although the relative contribution of these factors differs between roost types.     

Weather conditions affect the collective roosting behaviour of the Cattle Egret Bubulcus ibis

ABSTRACT

Capsule: Collective roosting behaviour of the Cattle Egret Bubulcus ibis was influenced by the weather and the season.

Aims: To document the roosting behaviour of the Cattle Egret and assess the relationship between weather conditions and four components of the roosting behaviour including the population size, duration of roost occupancy, the timing of roost gathering and the rate of arrival at roost.

Methods: We recorded the number and arrival times of individuals occupying a communal roost site in northeast Algeria in 2013–2014 between December and April.

Results: There was a seasonal decline of the flock size and rate of arrival and a seasonal increase in the duration of gathering. Weather conditions affected all variables assessed in roosting behaviour such that bad weather lowered the number of individuals in the roost, lengthened the duration and advanced the timing of gathering, and reduced the rate of gathering in the roost.

Conclusion: Our study highlights the importance of weather conditions in shaping the collective roosting behaviour of a gregarious species. Our results suggest that future changes in climatic conditions might influence the collective behaviour of the Cattle Egret in particular and gregarious birds in general.     

Experimental test of the mechanism underlying sexual segregation at communal roosts of harvestmen (Prionostemma spp.)

Closely related, ecologically similar species often roost in distinctly different habitats, and roosting patterns also vary within species in relation to sex, age and season. The causes of such variation are not well understood at either a proximate or ultimate level. We studied communal roosting in two congeneric species of Prionostemma harvestmen at a rainforest site in Nicaragua. Previous research showed that Prionostemma sp. 1 forms male‐biased communal roosts in tree‐root cavities, while Prionostemma sp. 2 forms communal roosts of variable but temporally stable sex ratios on spiny palms. Here, we investigate potential mechanisms underlying variation in roosting site choice between and within these syntopic species. First, we present the results of a field experiment designed to probe the mechanism underlying skewed roost sex ratios in Prionostemma sp. 2. Previous studies have suggested that these harvestmen use conspecific scent to locate communal roosts and that new roosts can be established via group translocation. Therefore, to test the hypothesis that skewed roost sex ratios in this species arise from sex differences in scent marks, we translocated single‐sex groups of ca. 30 individuals to each of 20 previously unoccupied spiny palms. Female release sites attracted new recruits of both sexes, while male release sites attracted almost exclusively males. We infer that Prionostemma sp. 2 females preferentially roost in sites scent‐marked by females and that this mechanism is sufficient to explain the skewed roost ratios. Further adding to knowledge of Prionostemma roosting behavior, we show that Prionostemma sp. 1 forms female‐biased communal roosts on spiny palms, that some roosts contain both species, and that the species composition is stable on a time scale of at least 2 weeks. To the best of our knowledge, this study is the first experimental test of mechanisms underlying sexual segregation at communal roosts in any taxon.     

Observations of social and reproductive biology of the bent-winged bat Miniopterus australis in northern Borneo

The small bent-winged bat Miniopterus australis was studied at low tropical latitudes north of the equator, principally in Subis cave, Niah, Sarawak, East Malaysia. During the course of field-work in 1957–58, most specimens were captured at roost in concavities in the cave ceiling, here termed "cupolas". At all months of observation, roosting groups varied from one to seven bats. Solitary bats were predominantly males, and multiple groups rarely included more than one male. It is suggested that the sexes differ in their response to a potential or familiar roosting site, depending on the prior occupation by other bats. Roosting behaviour did not vary with the progress of the reproductive cycle and seemed to have no epigamic function.
Observations of reproductive biology in 1957–58, supported by specimens captured in 1959–60, demonstrated that the species is monoestrous, with a brief annually recurrent breeding season in November-December. Copulation was observed in early November and preceded ovulation. In unovulated females taken in early December the right uterine horn was distended with spermatozoa. The single embryo subsequently implanted in the right horn, although in the three females examined the fertilized ovum derived from the left ovary.
Parturition occurred in late April and early May after a gestation period of 4 1/2–5 months. This period is considerably longer than the presumed species-specific minimum, observed at latitude 15 S. The prolonged gestation period is regarded as an adaptation to perennially low and variable food resources in an otherwise favourable environment, and there is evidence that the months of gestation and birth coincide with a period of limited seasonal increase in abundance of insect prey.