Forest Bats Research Articles

Bat fauna in Hidaka and Tokachi districts, central and eastern Hokkaido : (8) Capture records of bats in windbreak forests being located in the agricultural areas of Nakasatsunai Village

Bat fauna in Hidaka and Tokachi districts, central and eastern Hokkaido : (8) Capture records of bats in windbreak forests being located in the agricultural areas of Nakasatsunai Village

Temperature effects on metabolic rate and torpor in southern forest bats (Vespadelus regulus)

I measured the metabolic rate (MR) of four male southern forest bats (Vespadelus regulus; 5.5 g) exposed to a diurnal increase in air temperature (Ta) from 13 to 26°C, simulating conditions in natural tree roosts. Three bats remained in torpor throughout the day, despite the rise in Ta, whereas one bat aroused at a Ta of 25.2°C and was normothermic for 108 min until re-entering torpor when Ta declined in the afternoon. All bats aroused shortly after lights off. Torpid MR increased exponentially with rising Ta, yet even at 26°C remained only 16% of minimum resting MR at the same Ta. Rest-phase energy expenditure (12 h), including the estimated cost of an evening arousal, ranged from 0.62 to 1.23 kJ. Thus, torpor provides these small bats with an enormous reduction in energy consumption even at Ta close to their thermoneutral zone.

Roost selection by Big Brown Bats in Forests of Arkansas: Importance of Pine Snags and Open Forest Habitats to Males

Although Eptesicus fuscus (Big Brown Bat) has been widely studied, information on tree-roosting in forests by males is rare, and little information is available on tree roosting in the southeastern United States. Our objectives were to characterize diurnal summer roosts, primarily for male Big Brown Bats, and to determine relationships between forest structure and roost selection. We quantified 25 male roosts located via radiotelemetry, and describe an additional 9 maternity roosts for females. All roosts for both sexes were in Pinus echinata (Shortleaf Pine) snags, and 82% of roost snags were 15–25 cm diameter at breast height (dbh). Most (94%) roosts for both sexes were under loose bark. A logistic regression model differentiating male roost sites from random locations indicated males were more likely to roost in recently thinned, open-forest conditions (less canopy cover, more cut stumps, and fewer under-story stems) that contained abundant overstory pines ≥25 cm dbh and abundant snags. Males roosted primarily (84%) in stands that had recently undergone partial harvesting. Maintaining a supply of pine snags ≥15 cm dbh in relatively open forest habitats, including areas undergoing partial harvest, would provide roosting habitat for male Big Brown Bats in the Ouachita Mountains.

Systematic review of small fruit-eating bats (Artibeus) from the Guianas, and a re-evaluation of A. glaucus bogotensis

Abstract We studied molecular and morphological variation in small fruit-eating bats (Artibeus) in northern South America to establish species boundaries, evolutionary relationships, and distributional limits. Although this is a speciose genus with some of the most common bats in Neotropical forests, resolution of taxonomy and their identification has been difficult. Our molecular phylogeny based on Bayesian and parsimony analyses of cytochrome b variation includes a well supported topology of A. glaucus glaucus sister to a clade of A. gnomus and A. glaucus bogotensis indicating that A. glaucus is a paraphyletic amalgam. A re-assessment of morphology corroborates differences between A. g. bogotensis from the Andean valleys of Colombia east into the Guianas and A. g. glaucus from western Amazonia. Thus, we recognize A. bogotensis and A. glaucus as distinct and allopatrically occurring species. Based on a Kimura-2 parameter model of substitution for cytochrome b, there was 1.2% sequence divergence within A....

Male Seminole Bat Winter Roost‐Site Selection in a Managed Forest

Abstract: Understanding year‐round roost‐site selection is essential for managing forest bat populations. From January to March, 2004 to 2006, we used radiotelemetry to investigate winter roost‐site selection by Seminole bats (Lasiurus seminolus) on an intensively managed landscape with forested corridors in southeastern South Carolina, USA. We modeled roost‐site selection with logistic regression and used Akaike's Information Criterion for small samples (AICc) and Akaike weights to select models relating roost‐site selection to plot‐ and landscape‐level variables. We tracked 20 adult male bats to 71 individual roosts. Bats used a variety of roosting structures, including the canopy of overstory trees, understory vegetation, pine (Pinus spp.) needle clusters, and leaf litter. Roost height, structure type, and habitat type were influenced by changes in minimum nightly temperature. On warmer nights, bats selected taller trees in mature forest stands, but when minimum nightly temperatures were <4° C, bats typically were found roosting on or near the forest floor in mid‐rotation stands. We recommend avoiding prescribed burning in mid‐rotation stands on days when the previous night's temperature is <4 °C to minimize potential disturbance and direct mortality of bats roosting on or near the forest floor. We encourage forest managers to incorporate seasonal changes in roost‐site selection to create year‐round management strategies for forest bats in managed landscapes.

Prey Selection by Bats in Forests of Western Oregon

We investigated food habits and relationships between food resource abundance and activity of bats. We identified prey remains in guano collected from 337 individuals in the Oregon Coast Range. Guano analyses indicated that 2 species, long-legged myotis (Myotis volans) and Townsend's big-eared bat (Corynorhinus townsendii), consumed predominantly Lepidoptera; 4 species, California myotis (M. californicus), little brown myotis (M. lucifugus), Yuma myotis (M. yumanensis), and silver-haired bat (Lasionycteris noctivagans), consumed predominantly smaller insects likely of aquatic origin (Diptera and Trichoptera); and the remaining 4 species, long-eared myotis (M. evotis), fringed myotis (M. thysanodes), big brown bat (Eptesicus fuscus), and hoary bat (Lasiurus cinereus), consumed predominantly larger invertebrates of terrestrial origin (Lepidoptera, Coleoptera, Hemiptera, and Araneae). We hypothesized that bat activity in riparian areas would be correlated with abundance of preferred insect prey and used an information-theoretic approach to determine whether variability in bat activity was more strongly associated with captures of all insects, of taxa most frequently occurring in the diet, or of particular size classes of insects. We found strong associations between activity of small Myotis species and number of captures of small insects, but activities of larger Myotis species and of non-Myotis species were not associated with numbers of insects of any category.

Habitat Use of Pallid Bats in Coniferous Forests of Northern California

Limited information exists on the ecology and habitat requirements of the pallid bat (Antrozous pallidus) inhabiting forested ecosystems at the northern limits of its range. We used mist netting, radiotelemetry, and emergence counts at roosts to identify foraging and roosting habitat of pallid bats on the Plumas National Forest in northern California during summer 2007. Pallid bats used a variety of structures for day and night roosting, including live trees and snags, a rock crevice, and a building. Live trees and snags used for roosting were consistently tall in height, large in diameter, and located in mature stands in micro-sites with low percentages of overstory and mid-story cover. The height of roosting sites used by pallid bats in live trees and snags was low relative to the height of the stems selected for roosting. Size of foraging areas varied among sex and reproductive classes of pallid bats, with lactating females (1.56 km2 ± 0.88 SE) exhibiting the smallest foraging areas and post-lactating females (5.97 km2 ± 2.69 SE) having the largest foraging areas. Sierran mixed conifer and white fir habitats comprised significantly larger proportions of the available habitat within foraging areas of adult females than other habitats. Long distance movements during nightly foraging, > 2 km, were common for all sex and reproductive classes of pallid bats. These data indicate that pallid bats inhabiting coniferous forests choose alternate habitats in which to forage and roost from those typically used by the species in other regions of its distribution.

Scale‐Dependent Effects of Landscape Structure and Composition on Diurnal Roost Selection by Forest Bats

Abstract: Forest management affects the quality and availability of roost sites for forest‐dwelling bats, but information on roost selection beyond the scale of individual forest stands is limited. We evaluated effects of topography (elevation, slope, and proximity of roads and streams), forest habitat class, and landscape patch configuration on selection of summer diurnal roosts by 6 species of forest‐dwelling bats in a diverse forested landscape of the Ouachita Mountains, Arkansas, USA. Our objectives were to identify landscape attributes that potentially affect roost placement, determine whether commonalities exist among species in their response to landscape attributes, and evaluate the effects of scale. We modeled roost selection at 2 spatial scales (250‐ and 1,000‐m radius around each roost). For each species, parameters included in models differed between the 2 scales, and there were no shared parameters for 2 species. Average coefficients of determination (R2) for small‐scale models were generally higher than for large‐scale models. Abundance of certain forest habitat classes were included more often than patch configuration or topography in differentiating roost from random locations, regardless of scale, and most species were more likely to roost in areas containing abundant thinned forest. Among topographic metrics, big brown bats (Eptesicus fuscus) were more likely to roost at higher elevations; roosts of big brown bats, northern long‐eared bats (Myotis septentrionalis), and Seminole bats (Lasiurus seminolus) were influenced by slope; and big brown bats, evening bats (Nycticeius humeralis), and Seminole bats were more likely to roost closer to water than random. Northern long‐eared bats and red bats (Lasiurus borealis) were more likely to roost closer to roads, whereas eastern pipistrelles (Perimyotis subflavus) were more likely to roost further from roads than random. Common parameters in most models included 1) positive associations with group selection (5 of 6 species) and thinned mature forest (4 species) at the small scale; 2) negative associations with unmanaged mixed pine‐hardwood forest 50–99 years old at the large scale (4 species); 3) negative association with stands of immature pine 15–29 years old at the small scale (3 species); and 4) a positive association with largest patch index at the large scale (3 species). Our results suggest that, in a completely forested landscape, a variety of stand types, seral stages, and management conditions, varying in size and topographic location throughout the landscape, would likely provide the landscape components for roosting required to maintain a diverse community of forest bats in the Ouachita Mountains.

Blood Characteristics, Heart Mass, and Wing Morphology of Antillean Bats

Abstract. Oxygen-transport properties of blood and heart mass of 11 species of bats in the families Phyllostomidae, Mormoopidae, Noctilionidae, Molossidae, and Vespertilionidae were investigated and related to morphological characteristics of the wings and to phylogeny. These 11 species include all West Indian core species, and 85% of the assemblage of bats in the subtropical moist forest of northern Puerto Rico. Hematocrits (48.5%–64%) fall within values expected for bats. Diameter of red blood cells ranged from 4.2µm to 6.2µm. Heart mass (0.32g–0.01g) and hematocrit were significantly correlated to wing shape and wing loading (0.19 g/cm2–0.06 g/cm2), but not to phylogeny. The relationship between hematocrit and wing loading showed a negative slope.

Changes in prey abundance unlikely to explain the demography of a critically endangered Central European bat

Summary Recognizing the factor(s) that caused a demographic crash is a prerequisite to the development of a tailored population restoration plan. While habitat destruction leaves little scope for population persistence, cryptic habitat deterioration (for example through reduction of food resources) may similarly render an area totally inhospitable, while it still appears to have a suitable habitat configuration. Most European bat species have undergone dramatic declines over the past decades. Once among the most widespread and abundant bat species of Central Europe, the lesser horseshoe bat, Rhinolophus hipposideros (Bechstein 1800), is today extinct in many regions. Although changes in the agricultural landscape have been suggested as the major cause of decline, recent studies have shown that this bat forages almost exclusively in woodland, a habitat that has increased in area across continental Europe over the past decades. This suggests that habitat eradication per se is unlikely to be the main cause of decline. But could cryptic habitat deterioration play a harmful role? We looked at the abundance of insect prey in woodland in the vicinity of colonial roosts with diverging demographic status (extinct, declining or recovering populations), both in the Swiss lowlands (Swiss Plateau) and in the Alps. We predicted that population size correlates positively with prey abundance. Diet composition mirrored local insect prey abundance, confirming an opportunistic foraging strategy. Prey abundance showed marked seasonal variation, but did not differ between sites harbouring extinct, declining or recovering populations. There was also no difference in food abundance between extinct populations in the lowlands and recovering populations in the Alps. Synthesis and applications. Cryptic habitat deterioration through a reduction in prey abundance is unlikely to preclude recolonization of abandoned areas by presently recovering populations. However, sufficient areas of natural forest should be preserved or created around potential nursery roosts. Moreover, connectivity between forest patches must be ensured (by creation of hedges and tree lines) to prevent any spatial gap in recolonization within semi‐open agricultural landscapes. Other threatened European forest bats may also benefit from these measures.

Highly structured fission–fusion societies in an aerial-hawking, carnivorous bat

In some group-living animals, societies are far from being static but are instead dynamic entities encompassing multiple scales of organization. We found that maternity colonies of giant noctule bats, Nyctalus lasiopterus, form fissionefusion societies, where group composition in single tree roosts changes on a daily basis but social cohesion in the larger group is preserved. The population inside a small city park was comprised of three distinct but cryptic social groups coexisting in close proximity. Each social group used a distinct roosting area, but some overlap existed in the boundaries between them. Social groups were stable at least in the mid term because adult females were loyal to roosting areas and young females returned to their natal social groups in successive years. Our results suggest that distinct social groups with separate roosting areas may have existed for at least 14 years. The findings described support the hypothesis that roost-switching behaviour in forest bats permits the maintenance of social bonds between colony members and enhances knowledge about a colony’s roosting resources. Fissionefusion societies in forest bats might have evolved as a mechanism to cope with changing conditions in the environment by restructuring subgroups or adjusting subgroup size, to maximize the amount of information that can be transferred between colony members, or as a consequence of territory inheritance by philopatric female offspring. Other factors such as resource competition or kin selection could limit the size and composition of fissionefusion societies and promote strong social structuring within populations.

The sensory basis of roost finding in a forest bat,Nyctalus noctula

Tree cavities are a critical resource for most forest-dwelling bats. Yet, it is not known how bats search for new sites and, in particular, find entrances to cavities. Here, we evaluated the importance of different sensory channels for the detection of tree roosts by the noctule bat Nyctalus noctula. Specifically, we tested the role of three non-social cues (echo information, visual information and temperature-related cues) and two social sensory cues (conspecific echolocation calls and the presence of bat olfactory cues). We set up an experiment in a flight room that mimicked natural conditions. In the flight room, we trained wild-caught bats kept in captivity for a short while to find the entrance to an artificial tree cavity. We measured the bats' hole-finding performance based on echolocation cues alone and then presented the bat with one of four additional sensory cues. Our data show that conspecific echolocation calls clearly improved the bats' performance in finding tree holes, both from flying (long-range detection) and when they were crawling on the trunk (short range detection). The other cues we presented had no, or only weak, effects on performance, implying that detection of new cavities from a distance is difficult for noctules if no additional social cues, in particular calls from conspecifics, are present. We conclude that sensory constraints strongly limit the effectiveness of finding new cavities and may in turn promote sociality and acoustic information transfer among bats. As acoustic cues clearly increased the bats' detection performance, we suggest that eavesdropping is an important mechanism for reducing the costs of finding suitable roosts.

Bats in forests: conservation and management

Although bats are often thought of as cave dwellers, many species depend on forests for all or part of the year. Of the 45 species of bats in North America, more than half depend on forests, using the bark of trees, tree cavities, or canopy foliage as roosting sites. Over the past two decades it has become increasingly clear that bat conservation and management are strongly linked to the health of forests within their range. Initially driven by concern for endangered species-the Indiana bat, for example-forest ecologists, timber managers, government agencies, and conservation organizations have been altering management plans and silvicultural practices to better accommodate bat species. Bats in Forests presents the work of a variety of experts who address many aspects of the ecology and conservation of bats. The chapter authors describe bat behavior, including the selection of roosts, foraging patterns, and seasonal migration as they relate to forests. They also discuss forest management and its influence on bat habitat. Both public lands and privately owned forests are considered, as well as techniques for monitoring bat populations and activity. The important role bats play in the ecology of forests-from control of insects to nutrient recycling-is revealed by a number of authors. Bat ecologists, bat conservationists, forest ecologists, and forest managers will find in this book an indispensable synthesis of the topics that concern them.

Maternity roost site selection of big brown bats in ponderosa pine forests of the Channeled Scablands of northeastern Washington State, USA

Bats play a variety of ecological roles in forest ecosystems and forest management can impact habitat conditions for forest-dwelling bats. We examined the use and characteristics of roosts selected by reproductive female big brown bats ( Eptesicus fuscus) in the Channeled Scablands of northeastern Washington. We radio-tracked 14 bats to locate 36 roosts. Bats were found in colonies averaging 27 and these colonies switched roosts about every 3.7 days. Habitat variables were measured for the 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. Of the 36 roosts located, 34 were in natural tree cavities; 28 were in ponderosa pine ( Pinus ponderosa) and eight in quaking aspen ( Populus tremuloides). Dead tops of live pine trees were used significantly more as roosts than pine snags. Although there were significantly more roosts in trees >30 cm in diameter and >12 m high than what was available, roosts were not always the tallest tree in the stand. A significantly greater proportion of big brown bat roosts were found in open pine, aspen and mixed-aspen pine forests and less in grasslands and closed pine than expected. Forest management strategies should protect both large diameter snags and existing dead top live trees and maintain natural population levels of biological agents that create dead tops. Restoration of historic open conditions in ponderosa pine and aspen stands will provide improved habitat for big brown bats.

Relating bat species presence to habitat features in natural forests of Slovakia (Central Europe)

For the assessment of the habitat use of bats with consideration of a complexity of environmental features a large-scale multivariate canonical correspondence analysis (CCA) was performed. Data were collected in April–September (1999–2005) using mist-netting and bat-detectors ( n=209 samplings) in Slovakia ( n=160 sites). For the habitat description, 17 environmental variables that characterised the sampling site, tree-species composition and general character of surrounding forest were selected. In study sites, altogether 93% of Slovak chiropterofauna species were recorded but only 16 species (2466 individuals) were recorded in more than 5% of samplings. The most common and frequent species were Myotis mystacinus (frequency of occurrence=57%, species dominance=12%) and Myotis myotis (44%, 10%), followed by Barbastella barbastellus (32%, 6%), Plecotus auritus (32%, 6%), Nyctalus noctula (31%, 9%) and Myotis brandtii (31%, 7%). Of the tested environmental variables used in CCA analysis, 13 had significant influence on the species’ presence. On the base of gradients in ordination analysis, there were two main groups of species. In the first “true” forest bats group the tree-dwelling and gleaning species Myotis bechsteinii, Myotis nattereri and P. auritus dominated. Their occurrence was connected mainly with old forests of natural tree-species composition. The second group comprised species, which foraged in more open space or along the forest edge (with the farmland) and avoided closed interior (particularly Eptesicus serotinus, N. noctula, Nyctalus leisleri, Pipistrellus pipistrellus). The presence of mountain species Eptesicus nilssonii and Vespertilio murinus was associated mainly with dominance of spruce. Suggested predictive modelling of species composition in forest bat assemblages in conditions of natural forests can help in nature conservation.

Effects of reduced impact logging on bat biodiversity in terra firme forest of lowland Amazonia

Timber harvest is one of the main causes of degradation of Amazonian tropical forests, where bats represent important components of biodiversity. In addition, bats may represent keystone taxa in the Neotropics, as they are primary agents of pollination and seed dispersal for many pioneer plants. We assessed the impact of low harvest (18 m 3/ha), reduced impact logging (RIL) on population and community characteristics of phyllostomid bats in Amazonian terra firme forest of Brazil at 20–42 months post-harvest. Based on 103,680 net-meter-hours of netting in Tapajós National Forest, 2341 phyllostomids were captured, representing 42 species, 25 genera, and 4 broad feeding guilds. Population-level responses of common phyllostomids to RIL were minor, with 10 of 15 species evincing no change in mean abundance. Of those taxa responding to RIL (mean difference in number of individuals per site), three increased ( Artibeus concolor [0.46 individuals], Artibeus lituratus [3.88], and Glossophaga soricina [0.71]) and two decreased ( Carollia brevicauda [0.96] and Carollia perspicillata [14.04]) in abundance. Compositional (species distributions) and structural (rank distributions) aspects of bat assemblages differed between cut and control forests. More specifically, bat assemblages in cut forest had increased diversity and decreased dominance compared to control forest. Nonetheless, the proportional abundance of the five most common species, as a group, was similar in cut (86%) and control forest (88%), and frugivores dominated assemblages in both management types. Mean abundance of frugivores decreased (10.59 individuals per site) in response to RIL; however, this response was driven by decreases in C. perspicillata, the most abundant species in terra firme forest. Although RIL had only minor effects on biodiversity in the short-term, extrapolation to a long-term prospectus should be exercised with caution when applied to conservation or policy issues.

Prey Consumption of Insectivorous Bats in Coniferous Forests of North-Central Idaho

A considerable body of work has emerged on the ecology of insectivorous bats in forests of the Pacific Northwest, including dietary studies. Existing research in the Pacific Northwest on bat diets and prey consumption has emphasized populations of bats in Oregon. There are limited data for species inhabiting forests elsewhere in the region. We collected fecal samples from bats captured in mist nets set during May through August, 2004-05, in two watersheds in north-central Idaho that supported forests which were actively managed for timber production. We analyzed fecal samples of 183 bats of five species and compared the results to previously published data for these same species inhabiting forest habitats in the Pacific Northwest. Remains of 12 orders or classes of prey, along with 18 taxonomic families of insects, were identified in the diet of these bats. Prey items included Acari, Arachnida, Coleoptera, Diptera, Hemiptera, Homoptera, Hymenoptera, Isoptera, Lepidoptera, Neuroptera, Orthoptera, and Trich...

Describing roosts used by forest bats: the importance of microclimate

Adequate descriptions of roosting habitat are vital to the management and conservation of bats. However, most studies on bat roosting preference report only structural characteristics of roosts and surrounding habitat, and ignore potentially important factors in roost selection. I argue that the current methods for describing the roosting habitat of tree-roosting bats can be improved, and that more emphasis should be placed on designing studies to determine why bats choose particular roosts. Herein, I focus on measuring microclimate in roosts because it universally influences habitat selection. Specifically, roost temperature is easily measured and is likely an important microclimate variable used by bats in roost selection. Variation in structural characteristics of roosts is often assumed to correlate with variation in microclimate of the roost; however, empirical data are too scarce to verify this assumption. I suggest improvements to the current methods of describing roost characteristics and suggest the inclusion of new methods to describe microclimate. In summation, I argue that there are methods of measuring roost characteristics that may be beneficial to use in conjunction with the methods currently being used, and that microclimate should be considered when designing future studies.

Tree Selection and Landscape Analysis of Eastern Red Bat Day Roosts

ABSTRACT Declining bat populations and increasing demands on forest resources have prompted researchers to investigate tree roost selection of forest bats. Few studies, however, have investigated different spatial scales and landscape pattern as criteria for selection of tree roosts. In 1999 and 2000, we radiotracked 23 eastern red bats (Lasiurus borealis) to 64 day roosts. Using univariate and multivariate comparisons, we tested roost tree variables with random tree data at 3 circular spatial scales: roost tree, plot, and landscape. We found 15 variables that were entered in a stepwise discriminant analysis to best differentiate between the roost and random samples; 11 (73.3%) were landscape variables measured with a geographic information system. On average (x̄ ± SE), red bats roosted in deciduous trees (42.0 ± 2.1 cm dbh) that were located in plots with more (3.1 ± 0.1 m2) basal area, higher (84.0 ± 1.3) percentage of canopy closure, and lower (27.2 ± 2.2) percentage of groundcover than random plots. At the landscape scale (by percent magnitude), red bat buffers (1,000‐m‐radius circle) had significantly less development (81.6%), less feeding operations (70.4%), more deciduous (52.9%) and pine forest (63.8%), and fewer local roads (5.4%) but more trails (94.1%), open water (61.4%), wetland areas (80.4%), and stream areas (63.1%) than random buffers. Red bat roost trees were significantly closer (χ2 = 22.0088, df = 1, P < 0.001) to trails (106.2 ± 13.3 m) than to streams (279.4 ± 28.5 m). Our results suggest that red bats in our study area select roosts in mature riparian forests near trails, open water, and wetlands. The high percentage of landscape values in the discriminant analysis lends support to using landscape metrics as an investigative technique of resource selection. We recommend that managers consider landscape factors when protecting red bat day‐roost habitat.

Mist Net Effort Required to Inventory a Forest Bat Species Assemblage

Abstract: Little quantitative information exists about the survey effort necessary to inventory temperate bat species assemblages. We used a bootstrap resampling algorithm to estimate the number of mist net surveys required to capture individuals from 9 species at both study area and site levels using data collected in a forested watershed in northwestern California, USA, during 1996–2000. The mean number of simulated surveys required to capture individual species varied with species' rarity and ranged from 1.5 to 44.9. We retrospectively evaluated strategies to reduce required survey effort by subsampling data from 1996 to 1998 and tested the strategies in the field during 1999 and 2000. Using data from 1996 to 1998, the mean number of simulated surveys required to capture 8 out of 9 species was 26.3, but a 95% probability of capture required >61 surveys. Inventory efficiency, defined as the cumulative proportion of species detected per survey effort, improved for both the study area and individual sites by conducting surveys later in summer. We realized further improvements in study area inventory efficiency by focusing on productive sites. We found that 3 surveys conducted between 1 July and 10 September at each of 4 productive sites in this 10‐km2 study area resulted in the capture of 8 species annually. Quantitative estimation of the survey effort required to assess bat species occurrence improves the ability to plan and execute reliable, efficient inventories. Results from our study should be useful for planning inventories in nearby geographical areas and similar habitat types; further, the analytical methods we used to assess effort are broadly applicable to other survey methods and taxa.