Primary Roost Research Articles

Pre-Roost Habitats of Western Marsh Harriers (Circus aeruginosus) Wintering in Keoladeo National Park, Bharatpur in Northwestern India

Abstract I recorded information on pre-roost habitats of Western Marsh Harriers (Circus aeruginosus) near communal roost sites located in and around Keoladeo National Park (KNP), India, during three winters from 1997 to 2000. Harriers pre-roosted in different habitats in KNP compared to the surrounding areas (25-km radius). Harriers used trees as their main pre-roosting perches in KNP, but mainly used open fields in the surrounding areas. All nine tree species present near roost sites in KNP were used for pre-roosting. Among tree species used for pre-roosting, harriers preferred sacred fig (Ficus religiosa), a tall tree with a wide canopy. Babul (Vachellia nilotica) trees, though not preferred, were more utilized for pre-roosting, probably because of their abundance. The lack of suitable open areas near the primary roost site in KNP may help explain why harriers used trees as pre-roosting perches there. At other roost sites outside KNP where trees were sparse, harriers mainly pre-roosted on the ground. By perching on trees, harriers may be conspicuous to other arriving harriers, which likely helps the birds gather into a large roosting flock. Such large roosts may benefit harriers by providing protection from predators and a site where birds may obtain information on food resources. Although trees were used as pre-roosting sites at KNP, I did not observe any harriers roosting on trees overnight during the 3-yr study.

Network analysis of a northern long-eared bat (Myotis septentrionalis) maternity colony in a suburban forest patch

Abstract Many bat species are highly social, forming groups of conspecifics, particularly during the maternity season. In temperate North America, these social groups are typically comprised of closely related individuals or individuals that share some common trait (i.e. reproductive state or shared hibernacula from the previous winter). In the summer, when bats use forests for day-roosts, these social groups often demonstrate nonrandom patterns of periodically associating in common roosts and disassociating using different roosts as a ‘fission–fusion society’. As cave hibernating bat species in North America continue to decline due to the impacts of White-nose Syndrome, opportunities to describe these dynamics are becoming rare. Unfortunately, these patterns often are still poorly documented, yet understanding these behaviors is critical for species-specific habitat conservation and management. In our study, we tracked female northern long-eared bats (Myotis septentrionalis) to their day-roosts in a small, suburban forest fragment in coastal New York, USA, in the summers of 2018 and 2019. We confirmed that the bats shared roost sites and, using network analyses, analyzed social dynamics and space use. In contrast to previous research on this imperiled species in large, unfragmented core forests, we found a more dense, connected roost network that concentrated around forest patch edges. Unusual for this species, primary roosts were anthropogenic structures. Our findings suggest that northern long-eared bats can utilize small forest patches and that incorporation of specific types of anthropogenic roosts might be an effective strategy for long-term conservation in more urbanized landscapes where forest management actions to enhance day-roosting conditions are impractical and the risk of stochastic loss of roosts is high.

Indiana bat roosting behavior differs between urban and rural landscapes

Urbanization may negatively affect forest obligate bat species. We compared the roosting behavior of federally endangered Indiana bats (Myotis sodalis) in a fragmented site, located on the leading edge of a developing urban area (Indianapolis, IN), with a site of relatively contiguous forest cover in Indiana, USA, during the summers of 2013–2015. Bats in both sites used large standing dead trees and bat boxes with low levels of overhead canopy closure (fragmented site: 26.1 ± 11.0%, contiguous site: 20.1 ± 7.3%) as primary roosts (large groups of bats resident over many days). Between the 2 sites, secondary roosts (individual bats or small groups resident for only a few days) differed in canopy closure at the roost-scale (fragmented site: 66.9 ± 5.1%, contiguous site: 37.1 ± 9.3%); secondary roosts in the contiguous site resembled solar-exposed primary roosts. Bats in the fragmented site switched roosts less often (1.7 ± 0.5 switching events/bat, 5.8 ± 1.7 days of use/roosts) and traveled shorter distances between roosts (702 ± 211 m) than bats in the contiguous site (2.3 ± 0.6 switching events/bat, 2.4 ± 0.4 days of use/roosts; 1216 ± 337 m between roosts). This suggests that the fragmented site may have had low densities of available roosts, which may help explain the heavy use of bat boxes by bats in the fragmented site. These data suggest that urban populations of Indiana bats behave differently than those in rural areas, which managers should consider while managing for this species.

Roost selection of the endangered Spotted Greenshank (Tringa guttifer) in critical habitat in the Inner Gulf of Thailand

BackgroundRoost-site quality can significantly affect the individual fitness of shorebirds, but roost sites remain poorly described for many threatened species on the East Asian–Australasian Flyway. We studied roost-site selection of the globally endangered Spotted Greenshank (Tringa guttifer) in the Inner Gulf of Thailand, an area which supports approximately 24% of their global wintering population, during two non-breeding seasons (October 2014–May 2015 and December 2015–February 2016).MethodsWe measured nine variables associated with roost site characteristics including water depth, indicators of disturbance/predation risk, and associations with other shorebird species. We predicted that roost ponds with shallow water in proximity to foraging sites would receive higher usage than those further away.ResultsA total of 94 sites were measured of which 46 were used for roosts with 23 used repeatedly. All used sites were human-modified ponds, of which 44 were used for salt farming and two used for aquaculture. Roosts were on average 1.10 ± 0.78 (SE) km from foraging sites and 5.8 ± 2.4 cm deep. The most supported model indicated that roost sites were negatively associated with distance to foraging sites and positively associated with the presence of Grey Plover (Pluvialis squatarola) and water depth.ConclusionsTraditional saltpans and other artificial wetlands near (< 1 km) mudflats serve as the primary high-tide roost habitat in the Inner Gulf of Thailand for this Spotted Greenshank population and perhaps seven other globally threatened or near-threatened species. Critically, all observed roost sites are on private land with no formal protection and thus will require creative public–private partnerships to manage sustainably.

Thermoregulatory Requirements Shape Mating Opportunities of Male Proboscis Bats

The spatiotemporal distribution of females is a major factor affecting animal social systems. Predation risk and the distribution of feeding resources often determine where females are found, but abiotic factors (e.g. temperature) can also shape the distribution of females and therefore variation in social organization and mating systems. Given the predicted future changes in climatic variation, it is vital to understand how animal mating systems and the sexual selection process may be altered by temperature. In bats, female distribution is tightly linked to roosting ecology and particularly to the microclimatic conditions at the roost. Proboscis bats (Rhynchonycteris naso) form cohesive and stable multi-male-multi-female groups and inhabit exposed day roosts (e.g. tree trunks, vines, buildings). Strong selection to remain inconspicuous to visually oriented predators in the exposed day roosts has been suggested to promote a rather rare male mating strategy termed site-specific dominance where males defend females directly but are successful in doing so only in their own territory. The choice of open-roost structures can result in the bats roosting under direct sunlight, making individuals susceptible to overheating. Here we investigate whether regular relocations of R. naso social groups among male territories are a mechanism of behavioral thermoregulation. Our results suggest that in general R. naso choose the warmest suitable roost sites within a roost, possibly to minimize the energetic costs of thermoregulation. However, on days with high midday temperatures at the primary roost site, bats commonly relocate to alternative, cooler sites within their roosts. These thermoregulatory relocations entail that a social group regularly switches among the territories of several males. Thus, the need for behavioral thermoregulation determines the spatial distribution of females and shapes the mating opportunities of males during the day. This is supported by our result that territorial males defending primary roost sites are reproductively more successful than territorial males of alternate roost sites. In line with other studies, our findings suggest that the increase in ambient temperatures associated with climate change has the potential to affect the intensity of sexual selection in bat species and may have far-reaching behavioral, demographic and evolutionary consequences for their populations.

Effects of hierarchical roost removal on northern long-eared bat (Myotis septentrionalis) maternity colonies.

Forest roosting bats use a variety of ephemeral roosts such as snags and declining live trees. Although conservation of summer maternity habitat is considered critical for forest-roosting bats, bat response to roost loss still is poorly understood. To address this, we monitored 3 northern long-eared bat (Myotis septentrionalis) maternity colonies on Fort Knox Military Reservation, Kentucky, USA, before and after targeted roost removal during the dormant season when bats were hibernating in caves. We used 2 treatments: removal of a single highly used (primary) roost and removal of 24% of less used (secondary) roosts, and an un-manipulated control. Neither treatment altered the number of roosts used by individual bats, but secondary roost removal doubled the distances moved between sequentially used roosts. However, overall space use by and location of colonies was similar pre- and post-treatment. Patterns of roost use before and after removal treatments also were similar but bats maintained closer social connections after our treatments. Roost height, diameter at breast height, percent canopy openness, and roost species composition were similar pre- and post-treatment. We detected differences in the distribution of roosts among decay stages and crown classes pre- and post-roost removal, but this may have been a result of temperature differences between treatment years. Our results suggest that loss of a primary roost or ≤ 20% of secondary roosts in the dormant season may not cause northern long-eared bats to abandon roosting areas or substantially alter some roosting behaviors in the following active season when tree-roosts are used. Critically, tolerance limits to roost loss may be dependent upon local forest conditions, and continued research on this topic will be necessary for conservation of the northern long-eared bat across its range.

Diurnal and Nocturnal Roost Site Fidelity of Dunlin (Calidris Alpina Pacifica) at Humboldt Bay, California

AbstractShorebird roosts are often considered traditional, on the basis of predictable occupancy by large numbers of birds over long periods. However, fidelity of individuals to roosts at fine spatial and temporal scales, particularly at night, has rarely been described. We compared diurnal and nocturnal use of high-tide roosts by radiotagged Dunlin (Calidris alpina pacifica) wintering (November-March) at Humboldt Bay, California. Despite high fidelity to the study area, fidelity to particular roosts was relatively low and highly variable. At night, Dunlin used fewer roosts, were more faithful to primary roosts, and moved shorter distances between successive roosts than during the day. Day and night roosts differed in location, habitat, and distance from tidal flats. At night, Dunlin made greater use of pasture, and less use of islands and manmade structures. Day and night strategies of high-tide space use by Dunlin may be related to differences in food availability or predation danger. Our results illustrate that notions of tradition and site fidelity are scale-dependent and that knowledge of space use across the full range of environmental conditions is necessary for appropriate management of shorebird habitat.Fidelidad a los Sitios de Descanso Diurnos y Nocturnos en Calidris alpina pacifica en la Bahía de Humboldt, California

DIURNAL AND NOCTURNAL ROOST SITE FIDELITY OF DUNLIN (CALIDRIS ALPINA PACIFICA) AT HUMBOLDT BAY, CALIFORNIA

Abstract Shorebird roosts are often considered traditional, on the basis of predictable occupancy by large numbers of birds over long periods. However, fidelity of individuals to roosts at fine spatial and temporal scales, particularly at night, has rarely been described. We compared diurnal and nocturnal use of high-tide roosts by radiotagged Dunlin (Calidris alpina pacifica) wintering (November-March) at Humboldt Bay, California. Despite high fidelity to the study area, fidelity to particular roosts was relatively low and highly variable. At night, Dunlin used fewer roosts, were more faithful to primary roosts, and moved shorter distances between successive roosts than during the day. Day and night roosts differed in location, habitat, and distance from tidal flats. At night, Dunlin made greater use of pasture, and less use of islands and manmade structures. Day and night strategies of high-tide space use by Dunlin may be related to differences in food availability or predation danger. Our results illus...

The Relationship Between Habitat Characteristics and Demographic Performance of Northern Spotted Owls in Southern Oregon

AbstractWe used data from Northern Spotted Owl (Strix occidentalis caurina) territories to model the effects of habitat (particularly intermediate-aged forest stand types), climate, and nonhabitat covariates (i.e., age, sex) on owl reproductive rate and apparent survival in southwestern Oregon. Our best model for reproductive rate included an interaction between a cyclic, annual time trend and male breeding experience, with higher reproductive rates in even years compared to odd, particularly for males with previous breeding experience. Reproductive rate was also negatively related to the amount of winter precipitation and positively related to the proportion of old-growth forest near the owl territory center. Apparent survival was not associated with age, sex, climate or any of the intermediate-aged forest types, but was positively associated with the proportion of older forest near the territory center in a pseudothreshold pattern. The quadratic structure of the proportion of nonhabitat farther from the nest or primary roost site was also part of our best survival model. Survival decreased dramatically when the amount of nonhabitat exceeded ∼50%. Habitat fitness potential estimates (λ̂h) for 97 owl territories ranged from 0.29–1.09, with a mean of 0.86 ± 0.02. Owl territories with habitat fitness potentials &lt;1.0 were generally characterized by &lt;40%–50% old forest habitat near the territory center. Our results indicate that both apparent survival and reproductive rate are positively associated with older forest types close to the nest or primary roost site. We found no support for either a positive or negative direct effect of intermediate-aged forests on either survival or reproductive rate.

Use of Bat Boxes by a Maternity Colony of Indiana Myotis (Myotis sodalis)

Selection of maternity roosts by the federally endangered Indiana myotis (Myotis sodalis Miller and Allen) is a topic of great concern for wildlife managers. As part of annual monitoring of Indiana myotis at the Indianapolis International Airport, we observed M. sodalis using 2 of 974 available birdhouse-style bat boxes as maternity roosts. This represents the first reported use of birdhouse-style bat boxes as maternity roosts for M. sodalis. However, these 2 boxes were among 3204 artificial roosting structures on the site, including 259 triple and 715 single birdhouse-style bat boxes, many of which were in place for more than a decade and never used by Indiana myotis. Use of bat boxes by Indiana myotis may have been initiated by loss of a primary roost tree 2 years earlier.

FLIGHT BEHAVIOR OF BLACK AND TURKEY VULTURES: IMPLICATIONS FOR REDUCING BIRD–AIRCRAFT COLLISIONS

Abstract Mid-air collisions with black vultures (Coragyps atratus) and turkey vultures (Cathartes aura) regularly cause substantial damage to military and civilian aircraft. Information concerning the flight behavior of black and turkey vultures potentially could improve predictive models designed to reduce bird strikes by aircraft. We examined the flight behavior of black and turkey vultures at the Savannah River Site (SRS) in South Carolina, USA, and determined whether flight characteristics were predictable with respect to weather and time variables. We captured birds at their primary roost and subsequently relocated them via aerial telemetry from 11 February 2002 through 29 January 2003. One hundred eighty of 326 locations (55%) for 8 black vultures and 129 of 206 locations (63%) for 5 turkey vultures were of flying birds. Black vultures flew at an average altitude of 169 ± 115 (SD) m above ground level, whereas turkey vulture flight altitude averaged 163 ± 92 m. Our results contrast with those of pre...

HOME RANGES OF SYMPATRIC BLACK AND TURKEY VULTURES IN SOUTH CAROLINA

Abstract We examined home-range characteristics of seven Black Vultures (Coragyps atratus) and four Turkey Vultures (Cathartes aura) at the Savannah River Site, South Carolina. Birds were captured at their primary roost and tracked via aerial telemetry from 11 February 2002 through 29 January 2003. Mean annual home-range sizes (95% fixed kernel) for Black and Turkey Vultures were 12 399 ± 5199 ha [SE] and 34 053 ± 8567 ha, respectively. Black Vultures concentrated their movements around the primary roost, whereas Turkey Vultures demonstrated less site fidelity. Home-range sizes and time spent soaring for both species were much greater than reported for vultures residing in an agricultural landscape. We suggest that food resources at the heavily forested Savannah River Site were fewer and less predictable than in agricultural landscapes, requiring larger home ranges and increased time spent foraging. Rangos de Hogar de los Buitres Simpatricos Coragyps atratus y Cathartes aura en Carolina del Sur Resumen. E...

INDIANA BAT, MYOTIS SODALIS, MATERNITY ROOSTS IN THE SOUTHERN UNITED STATES

We characterized Indiana bat (Myotis sodalis) roosting habitat at three maternity colony sites in western North Carolina and eastern Tennessee. Using radio telemetry, we tracked six bats a total of 40 bat days (range 4–9 days/bat). In 1999, we located a primary roost in an eastern hemlock (Tsuga canadensis) snag (109 cm DBH) in the Nantahala National Forest, NC. In 2000, we located a primary roost in a pine (Pinus sp.) snag (39 cm DBH) in Great Smoky Mountains National Park (GSMNP), TN. Another primary roost was found in a pitch pine snag (P. rigida; 55 cm DBH) in GSMNP in 2001. Largest exit counts for the three colonies were 28, 23, and 81 bats. Primary roost sites were exposed to direct sunlight during most of the day. We also located six alternate roost trees: three pine snags, two red oak (Quercus rubra) snags, and one live sweet birch (Betula lenta). All three primary roosts located in this study were not used during subsequent summers. The eastern hemlock used in 1999 was still standing as of June 2001, while the two primary roosts in GSMNP had fallen within a year of being located. These records represent one of the first descriptions of Indiana bat maternity habitat in the southern United States.

HABITAT USE AND FORAGING BEHAVIOR OF TOWNSEND'S BIG-EARED BAT (CORYNORHINUS TOWNSENDII) IN COASTAL CALIFORNIA

Abstract Radiotracking studies of Townsend's big-eared bat (Corynorhinus townsendii) were conducted in grazed grassland and coastal forest (California bay, Douglas-fir, and redwood) at Point Reyes National Seashore in coastal central California. Radiotagged bats were used to determine the foraging patterns of both female and male bats and to locate alternate roost sites. The animals showed considerable loyalty to their primary roost sites even though the study was conducted after the nursery period had ended, when the bats would normally be dispersing for the season. Foraging patterns differed between male and female bats, with females traveling greater distances than males. Males consistently stayed close to the maternity colony both during day and night. Both sexes flew in the immediate vicinity of vegetation, both when foraging and when traveling from the roost to foraging areas. Foraging activity was concentrated primarily along the edges of riparian vegetation.

Selection of Summer Roosting Sites by Indiana Bats (Myotis sodalis) in Missouri

Summer roosting sites were studied at four maternity colonies of Indiana bats ( Myotis sodalis ) in northern Missouri. Colonies of Indiana bats used two types of roosts, primary and alternate, that differed in intensity of use, number, and probable function. Primary roosts were defined as roosts where use by >30 bats on more than one occasion was observed. The number of primary roosts per colony ranged from one to three. All primary roosts were in standing dead trees situated in trees exposed to direct sunlight. Alternate roosts were used by smaller numbers of bats. These roosts included both living and dead trees that typically were located within the shaded forest interior. Differences in patterns of use between types of roosts seemed to be influenced by weather conditions in that use of alternate roost trees increased during periods of elevated temperature and precipitation. Indiana bats have specific requirements for roost sites, but also must be able to relocate when loss of bark, tree fall, or other events render their current roost sites unusable. Practices of forest management within the summer range of Indiana bats should favor retention of large-diameter, mature, and senescent trees.

Home range and movements of postfledging American black ducks in eastern Maine

We monitored the movements of 97 female and 15 male juvenile American black ducks (Anas rubripes) in the vicinity of Moosehom National Wildlife Refuge in eastern Maine and southwestern New Brunswick from September through mid-December, 1985–1987. Movements were described by estimating home ranges and radial movements from the primary roost marsh. Overall home range sizes averaged 4987 ha (range 54 – 28 070 ha), and maximum distances moved from the roost averaged 9.9 km (range 0.9–42.8 km). Home ranges were linear (linearity index 2.8), and home range area and distance of movements from the roost both increased monthly. Ducks that used &gt;15% riverine habitat had larger home ranges and moved greater distances from the roost than ducks using &lt;15% riverine wetlands. Movements did not differ between ducks usually alone and those usually in flocks. Juvenile black ducks moved in small flocks and were often alone (34% of 355 observations). Most ducks showed fidelity to one roost-marsh complex from September until migration in late November. Daily and seasonal movement patterns were similar to those predicted for refuging systems.

Hemodilution with Anesthesia in the Bat, Antrozous pallidus

Lavia must provide effective insulation during cool times, and Rosevear (1965) thought the long fur might shield the bats from excessive insolation. The broad wing membranes allow for rapid heat dissipation in hot weather. Significantly, bats never remained at the primary roost site when temperatures even closely approached body temperature (assumed to be near 380C). Thus, by roosting at sites with temperatures well below 380C, bats could always dissipate heat passively from the wing membranes to the relatively cool air. Throughout this study my wife Rosemary helped locate and observe bats, and in May and June Jill E. Varnum assisted with this work.

The roles of energetics, water economy, foraging behavior, and geothermal refugia in the distribution of the bat,Macrotus californicus

Energy metabolism, thermoregulation, and water flux ofMacrotus californicus, the most northerly representative of the Phyllostomidae, were studied in the laboratory using standard methods, and energy metabolism and water fluxes were studied in the field using the doubly labelled water method together with a time budget. Daily energy expenditures of free-living bats averaged 22.8 kJ during the winter study period. Approximately 60% of this was allocated to resting metabolism costs while in the primary roosts (22 h/day).Macrotus californicus is unable to use torpor. The thermoneutral zone (TNZ) in this species is narrow (33 to 40 °C) and metabolic rate increased rapidly as ambient temperature decreased below the TNZ. Basal metabolic rate was 1.25 ml O2/g·h, or 24 J/g·h. Total thermal conductance below the TNZ. was 1.8 mW/g·°C, similar to values measured for other bats. Evaporative water loss showed a hyperbolic increase with increasing ambient temperature, and was approximately 1% of total body mass/h in the TNZ. The success of these bats as year-round residents in deserts in the southwestern United States is probably not due to special physiological adaptations, but to roosting and foraging behavior. They use geothermally-heated winter roost sites (stable year-round temperatures of approximately 29 °C) which minimize energy expenditures, and they have an energetically frugal pattern of foraging that relies on visual prey location. These seem to be the two major factors which have allowedM. californicus to invade the temperate zone.