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Townsend's Big-eared Bat - Corynorhinus townsendii

Image Copyright and Usage Information
Species of Concern
Native Species

Global Rank: G4
State Rank: S3
(see State Rank Reason below)


Agency Status
USFWS:
USFS: Sensitive - Known in Forests (LOLO)
BLM: SENSITIVE
FWP SWAP: SGCN3

External Links

State Rank Reason (see State Rank above)
Species is widespread, but uncommon and appears to occur at low densities. Disturbance of cave and mine roosts and the hard closure of occupied mines threaten long-term persistence.
  • Details on Status Ranking and Review
    Townsend's Big-eared Bat (Corynorhinus townsendii) Conservation Status Review
    Review Date = 09/26/2018
    Range Extent

    ScoreG - 200,000-2,500,000 km squared (about 80,000-1,000,000 square miles)

    Comment357,419 square Kilometers from Natural Heritage Program range maps.

    Long-term Trend

    ScoreE - Relatively Stable (±25% change)

    CommentHabitat is likely stable within +/- 25% since European settlement. Species forages in high clutter environments within forests or brushy areas across the state. It is unlikely that these habitats have changes significantly since European arrival. Roost habitats have likely increased as the species will use mines and buildings in the absence of suitable caves or other rock features.

    Short-term Trend

    ScoreU - Unknown. Short-term trend in population, range, area occupied, and number and condition of occurrences unknown.

    CommentNo data on trends available.

    Threats

    ScoreB - Moderate and imminent threat. Threat is moderate to severe and imminent for a significant proportion (20-60%) of the population or area.

    CommentDisturbance of roosting bats in caves and mines. Habitat loss through the closure of mines used by this species without installation of a bat friendly gate and collapse of mine adits.

    SeverityModerate - Major reduction of species population or long-term degradation or reduction of habitat in Montana, requiring 50-100 years for recovery.

    CommentIf animals can transition to other local roosts, recovery should be relatively quick. However suitable roosts may not exist within the immediate area

    ScopeModerate - 20-60% of total population or area affected

    CommentSince there are few visitors to most caves and mines in the state it is unlikely that this represents a threat to much of the population. However, the species is sensitive to visitation across much of the year amplifying the impacts of disturbance. Hard closure of mine adits may impact a small proportion of the population each year, but have a significant cumulative impact.

    ImmediacyHigh - Threat is operational (happening now) or imminent (within a year).

    CommentThreat is ongoing

    Intrinsic Vulnerability

    ScoreB - Moderately Vulnerable. Species exhibits moderate age of maturity, frequency of reproduction, and/or fecundity such that populations generally tend to recover from decreases in abundance over a period of several years (on the order of 5-20 years or 2-5 generations); or species has moderate dispersal capability such that extirpated populations generally become reestablished through natural recolonization (unaided by humans).

    CommentSpecies is long lived and has low fecundity. As these animals can fly, dispersal to and recolonization of extirpated populations is possible.

    Environmental Specificity

    ScoreB - Narrow. Specialist. Specific habitat(s) or other abiotic and/or biotic factors (see above) are used or required by the Element, but these key requirements are common and within the generalized range of the species within the area of interest.

    CommentSpecies is mostly dependent on forest habitats and cave roost sites which are rare on the landscape. Some evidence of building use in regions without karst features, sandstone outcrops, or mines.

    Raw Conservation Status Score

    Score 3.5 + 0 (geographic distribution) + 0 (environmental specificity) + 0 (long-term trend) + -0.75 (threats) = 2.75

 
General Description
Townsend’s Big-eared Bat is a moderately sized bat found throughout the state where suitable habitat exists, primarily near caves, mines, rock outcrops, and badlands. As the common name suggests, the species has large ears compared to its overall size. Although it never appear to be common in any portion of the state, it’s distribution is widespread and is among the most commonly observed species during cave surveys.

The species has large ears (30 to 39 millimeters) joined across forehead are a prominent feature in Townsend's Big-eared Bat; the tragus is long and pointed. The dorsal hairs are brownish at the tips, contrasting a little or considerably with the lighter underfur; ventral hairs are dark brownish-gray in color with brown to cinnamon tips. The hairs on the toes do not project beyond the toenails. There are two large, fleshy lumps on the snout, the basis for one of its common names, "lump-nosed bat." Total length is 90 to 113 millimeters; forearm length is 39.0 to 47.6 millimeters; adult mass is 5.0 to 13.5 grams. The greatest length of the skull is 15.2 to 17.4 millimeters; the skull has 36 teeth (Handley 1959, Kunz and Martin 1982, Nagorsen and Brigham 1993).

Diagnostic Characteristics
Townsend's Big-eared Bat differs from other Montana bats by its combination of extremely long, brownish ears that are joined at the base, the prominent lumps on the nose, the absence of large, white spots in the pelage (as with the Spotted Bat) and a dorsal pelage that is darker at the tips than the base (opposite that of the Pallid Bat, which is also larger-bodied).

The species is infrequently captured in mist nets. Nets set over water can be used, but captures are typically rare. The species is more frequently captured by placing nets within tight flyways in high clutter environments such as tall brush and densely forested areas. Surveys of caves and mines are an efficient way to detect the species as it is one of the most commonly encountered species within these features, particularly in the winter. Acoustic methods are effective and call sequences distinct, but echolocation is typically much quieter than other bat species and microphones must be placed close to roosts or foraging areas to ensure any individuals in the area are recorded.

Species Range
Montana Range Range Descriptions

Native

Western Hemisphere Range

 


Range Comments
Townsend’s Big-eared Bat has been documented across Montana in areas with suitable foraging and roosting habitats. These bats forage in high clutter environments such as tall brush and forest understory. Active season roosts include caves, mines, erosion cavities, and structures like buildings and bridges. As such only the short-grass prairies of northcentral and northeast Montana appear to be uninhabited by this species.

Observations in Montana Natural Heritage Program Database
Number of Observations: 449

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density

Recency

 

(Observations spanning multiple months or years are excluded from time charts)



Migration
Little information on movement is available for this species. Townsend's Big-eared Bat is present yearround in Montana, with summer or winter records from several localities (Hoffmann et al. 1969, Swenson and Shanks 1979, Hendricks 2000, Hendricks et al. 2000, Hendricks and Kampwerth 2001), but movements of individuals between active season roosts and hibernacula have not been reported or studied. The species has been consistently detected in several caves in western and central Montana in both the active and hibernation seasons. While not conclusive, anecdotally this supports the hypothesis that seasonal movement is limited.

Habitat
Of all of Montana’s bat species, Townsend’s Big-eared Bat is the most closely associated with caves, mines, and other similar features such as talus caves and erosion cavities found in badlands and river breaks. Caves and abandoned mines are used for maternity roosts and hibernacula (Worthington 1991, Hendricks et al. 1996, Hendricks 2000, Hendricks et al. 2000, Foresman 2012, Hendricks and Kampwerth 2001); use of buildings in late summer has also been reported (Swenson and Shanks 1979). In hibernacula, ambient temperatures ranged from -1.0 to 8.0 degrees (30 to 46 when torpid Townsend's Big-eared Bats were present) (Hendricks and Kampwerth 2001). Temperatures at maternity roosts are poorly documented; the temperature was 12 degrees (54 in mid-July near a colony in an abandoned mine in Lake County), and 18 degrees (66 in August near a colony in a large and relatively open cave chamber in Lewis and Clark County). Most caves and mines in Montana appear to be too cool in summer for use as maternity roosts.

Ecological Systems Associated with this Species
  • Details on Creation and Suggested Uses and Limitations
    How Associations Were Made
    We associated the use and habitat quality (common or occasional) of each of the 82 ecological systems mapped in Montana for vertebrate animal species that regularly breed, overwinter, or migrate through the state by:
    1. Using personal observations and reviewing literature that summarize the breeding, overwintering, or migratory habitat requirements of each species (Dobkin 1992, Hart et al. 1998, Hutto and Young 1999, Maxell 2000, Foresman 2012, Adams 2003, and Werner et al. 2004);
    2. Evaluating structural characteristics and distribution of each ecological system relative to the species' range and habitat requirements;
    3. Examining the observation records for each species in the state-wide point observation database associated with each ecological system;
    4. Calculating the percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system to get a measure of "observations versus availability of habitat".
    Species that breed in Montana were only evaluated for breeding habitat use, species that only overwinter in Montana were only evaluated for overwintering habitat use, and species that only migrate through Montana were only evaluated for migratory habitat use.  In general, species were listed as associated with an ecological system if structural characteristics of used habitat documented in the literature were present in the ecological system or large numbers of point observations were associated with the ecological system.  However, species were not listed as associated with an ecological system if there was no support in the literature for use of structural characteristics in an ecological system, even if point observations were associated with that system.  Common versus occasional association with an ecological system was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species as represented in scientific literature.  The percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system was also used to guide assignment of common versus occasional association.  If you have any questions or comments on species associations with ecological systems, please contact the Montana Natural Heritage Program's Senior Zoologist.

    Suggested Uses and Limitations
    Species associations with ecological systems should be used to generate potential lists of species that may occupy broader landscapes for the purposes of landscape-level planning.  These potential lists of species should not be used in place of documented occurrences of species (this information can be requested at: mtnhp.org/requests) or systematic surveys for species and evaluations of habitat at a local site level by trained biologists.  Users of this information should be aware that the land cover data used to generate species associations is based on imagery from the late 1990s and early 2000s and was only intended to be used at broader landscape scales.  Land cover mapping accuracy is particularly problematic when the systems occur as small patches or where the land cover types have been altered over the past decade.  Thus, particular caution should be used when using the associations in assessments of smaller areas (e.g., evaluations of public land survey sections).  Finally, although a species may be associated with a particular ecological system within its known geographic range, portions of that ecological system may occur outside of the species' known geographic range.

    Literature Cited
    • Adams, R.A.  2003.  Bats of the Rocky Mountain West; natural history, ecology, and conservation.  Boulder, CO: University Press of Colorado.  289 p.
    • Dobkin, D. S.  1992.  Neotropical migrant land birds in the Northern Rockies and Great Plains. USDA Forest Service, Northern Region. Publication No. R1-93-34.  Missoula, MT.
    • Foresman, K.R.  2012.  Mammals of Montana.  Second edition.  Mountain Press Publishing, Missoula, Montana.  429 pp.
    • Hart, M.M., W.A. Williams, P.C. Thornton, K.P. McLaughlin, C.M. Tobalske, B.A. Maxell, D.P. Hendricks, C.R. Peterson, and R.L. Redmond. 1998.  Montana atlas of terrestrial vertebrates.  Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, MT.  1302 p.
    • Hutto, R.L. and J.S. Young.  1999.  Habitat relationships of landbirds in the Northern Region, USDA Forest Service, Rocky Mountain Research Station RMRS-GTR-32.  72 p.
    • Maxell, B.A.  2000.  Management of Montana's amphibians: a review of factors that may present a risk to population viability and accounts on the identification, distribution, taxonomy, habitat use, natural history, and the status and conservation of individual species.  Report to U.S. Forest Service Region 1.  Missoula, MT: Wildlife Biology Program, University of Montana.  161 p.
    • Werner, J.K., B.A. Maxell, P. Hendricks, and D. Flath.  2004.  Amphibians and reptiles of Montana.  Missoula, MT: Mountain Press Publishing Company. 262 p.

Food Habits
Townsend's Big-eared Bat feeds on various nocturnal flying insects near the foliage of trees and shrubs, but appears to specialize primarily on small moths (Kunz and Martin 1982); other insects in the diet include lacewings, beetles, true flies, and wasps. There are reports of gleaning insects from foliage, but most are captured in the air, often near foliage. In a California study, individuals hunted primarily around the perimeter of trees, usually 10 to 30 meters off the ground, between mid-canopy and near the top of the canopy (Fellers and Pierson 2002). The diet and foraging behavior of Townsend's Big-eared Bat in Montana have not been reported or studied.

Ecology
Females form maternity colonies during the spring and summer. Colonies are typically composed of 20 to 180 females, each giving birth to one pup after a gestation period of 55 to 100 days (Pearson et al. 1952, Genter personal observation). Pups are able to fly in 3 weeks and are weaned at 6 weeks. Both sexes congregate at cooler caverns (called swarming sites) in late summer/early fall.

Townsend's Big-eared Bat emerges from day roosts in coastal California and central Oregon within an hour after sunset (Dobkin et al. 1995, Fellers and Pierson 2002); limited information from Montana indicates a similar emergence time (P. Hendricks and J. Carlson personal observation). In Oregon, individuals moved up to 24 kilometers from hibernacula to foraging areas (Dobkin et al. 1995). In California, foraging individuals traveled less than 10.5 kilometers from primary day roosts and tended to forage in the same areas each night. The mean center of activity for females was 3.2 kilometers from the roost, and 1.3 kilometers for males; 41 to 88% of tagged bats returned to their roost each night. Individual bats used nine alternate roosts (Fellers and Pierson 2002).

Townsend's Big-eared Bat tends to hibernate singly, but does occur in clusters during winter in some areas (Schmidly 1991). It tends not to associate closely in day roosts and hibernacula with other species of bats, although individuals of other species may be present elsewhere in the roost (Handley 1959, Kunz and Martin 1982, Genter 1986, Choate and Anderson 1997, Kuenzi et al. 1999). In Montana, Townsend's Big-eared Bat has been found at summer and winter roosts in the presence of other bat species (Swenson and Shanks 1979, Worthington 1991, Hendricks et al. 2000, Hendricks and Kampwerth 2001), although it usually hibernates in the open and alone, rather than in clusters or wedged in cracks.

Crude population density in Oklahoma was estimated at one bat per hectare (Humphrey and Kunz 1976, Kunz and Martin 1982), about 3 to 4 times greater than that reported in California (Pearson et al. 1952). Natality rates for colonies of adult females typically exceed 90%, but may be as low as 35% (Kunz and Martin 1982, Fellers 2000); pre-weaning post-natal mortality of adults generally is 4 to 5%. Adult survivorship is relatively high (about 70 to 80% in females in California). Regional population increases in California may be dependent on the establishment of new nursery colonies (Pearson et al. 1952), since colony size has been reported to remain static year after year. Predation has been suggested as the primary limiting factor in Kansas and Oklahoma (Handley 1959), although lack of suitable roosting habitat seems more likely to limit population size in this region (Humphrey and Kunz 1976). Predators of Townsend's Big-eared Bat are poorly documented, but include the Black Rat and Eastern Woodrat (Clark et al. 1990, Fellers 2000), as well as the Black Ratsnake, Spotted Skunk, Domestic Cat, and Ringtail (Pierson et al. 1999); predators can significantly depress reproductive success in some maternity colonies. No demographic data or estimates of population size are available for any population in Montana, nor have any predators been documented.

Reproductive Characteristics
No published studies are available on the reproductive biology of this species in Montana, and other documentation is very limited. Only five maternity colonies are known in Montana, with an estimated size in recent years of 25 to 100 adult females each. Lone adult females captured in early August in the Pryor Mountains were non-lactating (P. Hendricks and J. Carlson personal observation); flying juveniles appear in the same region sometime between late June and early September (Worthington 1991).

Based upon studies in other areas of the species' range mating begins in autumn and continues into winter. Ovulation and fertilization are delayed until late winter/early spring. Gestation lasts 2.0 to 3.5 months. A single young is born during a five week period, beginning mainly in late May in California, June in west Texas, and the second week of July in Washington (Pearson et al. 1952, Easterla 1973, Kunz and Martin 1982). Young can fly at 2.5 to 3.0 weeks, and are weaned by 6 weeks. In central California, summer colonies start to break up in August when the older young are just over 3 months old. Females become sexually mature their first summer; males are not sexually active until their second year. Young fly at 1 month of age and are weaned at 2 months. Most adult females breed every year. Maternity colonies are often smaller than 100 adult females, but up to 550 adult females are present in some (Easterla 1973, Humphrey and Kunz 1976, Pierson et al. 1991, Szewczak et al. 1998, Fellers 2000, Sherwin et al. 2000, Fellers and Pierson 2002). Males roost separately (apparently solitary) during this time. Maximum longevity is estimated to be about 16 to 17 years (Kunz and Martin 1982).

Management
The response by Townsend's Big-eared Bats to human activities is largely undocumented in Montana. The maternity colony at Lewis and Clark Caverns has persisted for over a century, even though it is exposed daily to tour groups. In eastern Montana, numerous abandoned coal mines have been completely closed in recent decades, several of which were used as hibernacula; these mines are no longer accessible to bats. Abandoned mine reclamation has also been underway in western Montana during the same time. During the last decade, mine surveys prior to closure have been undertaken by land management agencies to determine the potential of abandoned mines as bat habitat. In some cases bat-friendly gates were installed at known Townsend's Big-eared Bat roosts, and the roosts have continued to be used after gate installation (Hendricks 1999, Hendricks and Kampwerth 2001). Some caves in the Pryor Mountains and Little Rocky Mountains with documented use by Townsend's Big-eared Bat are protected with bat-friendly gates (Worthington 1991, Hendricks et al. 2000). Abandoned mines should be surveyed for Townsend's Big-eared Bats or other bat species prior to any reclamation activity. Surveys should follow protocols in the conservation assessment and conservation strategy (Pierson et al. 1999). Installation of bat-friendly gates should be considered as a protective measure for all Townsend's Big-eared Bat roosts. Other land management activity (cave management, pesticide spraying, timber harvest, other vegetation conversion) at or near known roosts should also be conducted according to the best management practices outlined in the conservation assessment and strategy. Maternity roosts and hibernacula should be routinely monitored to establish population trends across the state. Undiscovered maternity colonies and hibernacula undoubtedly exist in Montana. All observations of Townsend's Big-eared Bat roosts should be reported to the appropriate land management agency, the Montana Natural Heritage Program, or the Montana Department of Fish, Wildlife and Parks.

References
  • Literature Cited AboveLegend:   View Online Publication
    • Choate, J. R. and J. M. Anderson. 1997. Bats of Jewel Cave National Monument, South Dakota. Prairie Naturalist 29:39-47.
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    • Dobkin, D. S., R. D. Gettinger, and M. G. Gerdes. 1995. Springtime movements, roost use, and foraging activity of Townsend's big-eared bat (Plecotus townsendii) in central Oregon. Great Basin Naturalist 55:315-321.
    • Easterla, D. A. 1973. Ecology of the 18 species of Chiroptera at Big Bend National Park, Texas. Part I and II. Northwest Missouri State University Studies 34:1-165.
    • Fellers, G. M. 2000. Predation on Corynorhinus townsendii by Rattus rattus. Southwestern Naturalist 45:524-527
    • Fellers, G. M. and E. D. Pierson. 2002. Habitat use and foraging behavior of Townsend's big-eared bat (Corynorhinus townsendii) in coastal California. Journal of Mammalogy 83:167-177.
    • Foresman, K.R. 2012. Mammals of Montana. Second edition. Mountain Press Publishing, Missoula, Montana. 429 pp.
    • Genter, D. L. 1986. Wintering bats of the upper Snake River plain: occurrence in lava-tube caves. Great Basin Naturalist 46(2):241-244.
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    • Hendricks, P. 2000. Preliminary bat inventory of caves and abandoned mines on BLM lands, Judith Mountains, Montana. Montana Natural Heritage Program, Helena, Montana. 21 pp.
    • Hendricks, P. and D. Kampwerth. 2001. Roost environments for bats using abandoned mines in southwestern Montana : a preliminary assessment. Report to the U.S. Bureau of Land Management. Montana Natural Heritage Program, Helena, Montana. 19 pp.
    • Hendricks, P., D. L. Genter, and S. Martinez. 2000. Bats of Azure Cave and the Little Rocky Mountains, Montana. Canadian Field-Naturalist 114 :89-97.
    • Hendricks, P., K.A. Jurist, D.L. Genter and J.D. Reichel. 1996. Bats of the Kootenai National Forest, Montana. Unpublished report. Montana Natural Heritage Program, Helena, Montana. 99 pp.
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    • Pierson, E. D., W. E. Rainey, and D. M. Koontz. 1991. Bats and mines: experimental mitigation for Townsend's big-eared bat at the McLaughlin Mine in California. In: R.D. Comer et al. eds. Proceedings V: issues and technology in the management of impacted wildlife. pp. 31-44. Thorne Ecological Institute, April 8-10, Snowmass, Colorado.
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  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
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    • Worthington, D.J. and H.N. Ross. 1990. Abundance and distribution of bats in the Pryor Mountains of south central Montana. Unpublished report for the Montana Natural Heritage Program. 20 p.
    • Zukal, J., J. Pikula, and H. Bandouchova. 2015. Bats as bioindicators of heavy metal pollution: history and prospect. Mammalian Biology 80(3): 220-227.
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Citation for data on this website:
Townsend's Big-eared Bat — Corynorhinus townsendii.  Montana Field Guide.  .  Retrieved on , from