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Montana Animal Field Guide

Montana Field Guides

Hoary Bat - Lasiurus cinereus

Species of Concern

Global Rank: G3G4
State Rank: S3

Agency Status


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General Description
The Hoary Bat is a large lasurine (20 to 35 g) with long pointed wings and heavily-furred interfemoral membrane. Pelage overall is frosted or hoary (mixed brownish and grayish with white-tipped hairs, wrist and shoulder patches whitish), yellowish on the throat, forearm length about 46 to 55 mm. Ears are short and rounded, rimmed in dark brown or black, tragus short and broad. It has large teeth; dental formula I 1/3, C 1/1, P 2/2, M 3/3 (Shump and Shump 1982, Adams 2003).

Diagnostic Characteristics
Hoary Bat is the largest bat species found in Montana, and only one of two with an interfemoral membrane completely furred on the dorsal surface, the other being the Eastern Red Bat. The Hoary Bat has a distinctive appearance along with its large size (35 g in weight, to about 140 mm in total length): dorsal pelage in is a mixture of browns and grays, tinges with white, giving the bat a frosted or hoary appearance (Shump and Shump 1982), unlike the reddish dorsal pelage of the smaller Eastern Red Bat. Definitive Hoary Bat calls are also of lower characteristic frequency and appearance: < 23 kHz lasting up to 20 milliseconds for Hoary versus 38-50 kHz lasting > 10 milliseconds for Eastern Red.

Species Range
Montana Range

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Western Hemisphere Range


Summary of Observations Submitted for Montana
Number of Observations: 1329

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



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

Hoary Bat is migratory and only a summer resident in Montana, with records from early June through September. Normal arrival and departure dates are uncertain.

During the summer, Hoary Bats occupy forested areas. A female with two naked pups was found in mid-July using a wooden bridge in Stillwater County as a temporary day roost (Hendricks et al. 2005) but no other Montana roosts have been reported. Often captured foraging over water sources embedded within forested terrain, both conifer and hardwood, as well as along riparian corridors. Reported in Montana over a broad elevation range (579 to 2774 m; 1900 to 9100 ft) during August, the highest record from treeline along the Gravelly Range road (Madison County), the lowest from the Yellowstone River near Sidney (Richland County); probably most common throughout summer in Montana at lower elevations.
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 (high, medium, or low) 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 2001, 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 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 associated as using 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 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.  High, medium, and low habitat quality was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species in the 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 assignments of habitat quality.  If you have any questions or comments on species associations with ecological systems, please contact Bryce Maxell at or (406) 444-3655.

    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: 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.  2001.  The wild mammals of Montana.  Special Publication No. 12.  Lawrence, KS: The American Society of Mammalogists.  278 p.
    • 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
Reported to favor moths (Shump and Shump 1982), but stomach contents of 7 individuals captured in Carter County (Jones et al. 1973) revealed beetles (Scarabidae and Dytiscidae), moths, true bugs (Corixidae, Miridae), leafhoppers (Cicindellidae), lacewings (Myremeleontidae, Hemerobiidae), and true flies (Anthomyiidae, Calliphoridae, Tipulidae, Chironomidae, Muscidae). They are also carnivorous, and have been reported to attack, kill, and eat pipistrelle bats (Shump and Shump 1982, Adams 2003).

Little information available from Montana: a female Hoary Bat with pups roosted 5.3 m above ground on 16 July on the underside of a wooden bridge in Stillwater County, the first time reported for this species (Hendricks et al. 2005) and within 1.5 m of a small maternity colony of Big Brown Bats; a desiccated adult was found 17 June 1974 impaled on a hawthorn near Goat Haunt Ranger Station in Glacier National Park (Roemer 1995). Throughout the range, this bat appears to be solitary, roosting primarily in trees but reported infrequently from caves (dead individuals), squirrel nests, and clinging to the sides of buildings. Most day roosts are 3 to 5 m above ground, and in such trees as elm, plum, box elder, osage orange, and black cherry. Their flight is swift and direct; they generally emerge at dusk (although in winter they may arouse from hibernation and forage on warm afternoons), and most captures occur 3 to 4 hours after sunset. No important predators of Hoary Bats are known but undoubtedly hawks and owls capture some, and there is at least one report of predation by a snake (Shump and Shump 1982).

Reproductive Characteristics
Through 2010, reproductive status in Montana, based on examination of > 120 individuals, is as follows: for adult female Hoary Bats, pregnant (13 June to 10 July), lactating (11 June to 2 August), post-lactating (15-29 July), nulliparous (21 July to 15 August); for adult male Hoary Bat, non-reproductive (14 June to 30 August), scrotal (10 July to 31 August); for young of the year: naked pups (16 July), volant juveniles (16 July to 31 August). See descriptions in Jones et al. (1973) for summary from Carter County, and Hendricks et al. (2005) for observation of adult female with naked pups. Litter size reported from other regions is usually 2, ranging 1 to 4 pups. Mating probably occurs during late summer and autumn migration, but implantation delayed until spring (Shump and Shump 1982).

No management measures have been enacted specifically for the protection of Hoary Bat in Montana. There are a number of reports of fatal collisions with barbed wire, including in Yellowstone County (Swenson and Bent 1977, Shump and Shump 1982). This species is vulnerable to collision with wind turbines at wind farms (Johnson et al. 2003, Arnett et al. 2008). Fatalities of migrating Hoary Bats may be predictable events, because this species appears to be drawn to prominent landmarks that they see during migration, and this is related to autumn flocking and mating behaviors (Cryan and Brown 2007). Increasing rotor start-up wind speed or changing the pitch angle of blades and lowering the required generator speed for electricity production had the same effect in reducing bat fatalities at an Alberta wind farm by 57-60% (Baerwald et al. 2009) and may be promising mitigation techniques at wind energy facilities.

  • Literature Cited AboveLegend:   View Online Publication
    • Adams, R.A. 2003. Bats of the Rocky Mountain West: natural history, ecology and conservation. University Press of Colorado: Boulder, CO. 289 pp.
    • Arnett, E. ., W.K. Brown, W.P. Erickson, J.K. Fiedler, B.L. Hamilton, T.H. Henry, A. Jain. 2008. Patterns of bat fatalities at wind energy facilities in North America. Journal of Wildlife Management 72(1): 61-78.
    • Baerwald, E.F., J. Edworthy, M. Holder, and R.M. R. Barclay. 2009. A large-scale mitigation experiment to reduce bat fatalities at wind energy facilities. Journal of Wildlife Management 73(7): 1077-1081.
    • Cryan, P. M. and A. C. Brown. 2007. Migration of bats past a remote island offers clues toward the problem of bat fatalities at wind turbines. Biological Conservation 139(1-2): 1-11.
    • Hendricks, P., J. Johnson, S. Lenard, and C. Currier. 2005. Use of a bridge for day roosting by the hoary bat, Lasiurus cinereus. Canadian Field-Naturalist 119(1):132.
    • Johnson, G., W. Erickson, J. White, and R. McKinney. 2003. Avian and bat mortality during the first year of operation at the Klondike phase I Wind Project, Sherman County, Oregon. Prepared for Northwestern Wind Power by West, Inc., Cheyenne, WY. 17 pp.
    • Jones, J.K., Jr., R.P. Lampe, C.A. Spenrath, and T.H. Kunz. 1973. Notes on the distribution and natural history of bats in southeastern Montana. Occasional papers (Texas Tech University Museum) 15:1-11.
    • Roemer, D. 1995. Montana Chiroptera from the University of Montana mammals collection. Unpublished report. Environmental Studies Department, University of Montana, Missoula. 22 pp.
    • Shump, K. A., Jr. and A. U. Shump. 1982. Lasiurus cinereus. American Society of Mammalogists, Lawrence, KS. Mammalian Species No. 185:1-5.
    • Swenson, J. E. and J. C. Bent. 1977. The bats of Yellowstone County, southcentral Montana. Proceedings of the Montana Academy of Sciences 37:82-84.
  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Barclay, R. M. 1986. The echolocation calls of Hoary (Lasiurus cinereus) and Silver-haired (Lasionycteris noctivagans) bats as adaptations for long- versus short-range foraging strategies and the consequences for prey selection. Canadian Journal of Zoology 64:2700-2705.
    • Fitzgerald, T. 1989. New records of bats from northeastern Colorado. Journal of the Colorado-Wyoming Academy of Science 21:22.
    • Foresman, K.R. 2001. The wild mammals of Montana. American Society of Mammologists, Special Publication Number 12. Lawrence, KS. 278 pp.
    • 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.
    • Perkins, M. J. and S. P. Cross. 1988. Differential use of some coniferous forest habitats by hoary and silver-haired bats in Oregon. The Murrelet 69:21-24.
    • Reid, F. 2006. Peterson Field Guide to Mammals of North America, 4th Edition. Houghton Mifflin Company: Boston and New York, 608 pp.
    • Thompson, L.S. 1982. Distribution of Montana amphibians, reptiles, and mammals. Bozeman: Montana Audubon Council. 24 pp.
    • Waage, Bruce C., 1988, Western Energy Company Rosebud Mine, Colstrip, Montana: Annual Wildlife Monitoring Report, 1988 Field Season. December 1988.
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Citation for data on this website:
Hoary Bat — Lasiurus cinereus.  Montana Field Guide.  Montana Natural Heritage Program and Montana Fish, Wildlife and Parks.  Retrieved on May 24, 2016, from