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Montana Animal Field Guide

Montana Field Guides

Eastern Red Bat - Lasiurus borealis

Potential Species of Concern

Global Rank: G3G4
State Rank: SU

Agency Status


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General Description
The Eastern Red Bat is a moderately-sized lasurine (7 to 15 g) with long pointed wings and heavily-furred interfemoral membrane. Pelage overall is reddish, lighter on the belly than the back. Ears are low and rounded, tragus triangular, forearm length about 39 to 41 mm. It has large teeth; the dental formula is I 1/3, C 1/1, P 2/2, M 3/3 (Shump and Shump 1982a, Adams 2003).

Diagnostic Characteristics
Eastern Red Bat has a distinctive pelage: upper parts are brick-red to rusty-red washed with white, under parts are slightly paler. Only one other bat species in Montana, Hoary Bat, has an interfemoral membrane completely furred on the dorsal surface. The Hoary Bat is much larger (2.0-2.5 X in body wieght, 17-20% longer in total length) than the Eastern Red Bat, and its dorsal pelage is mixed grayish and brownish, tinged with while, giving it a frosty or hoary appearance, not uniformly reddish (Shump and Shump 1982a). Definitive Eastern Red Bat calls are also of higher characteristic frequency: 38-50 kHz lasting > 10 milliseconds for Eastern Red versus < 23 kHz lasting up to 20 milliseconds for Hoary.

Species Range
Montana Range

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Western Hemisphere Range


Summary of Observations Submitted for Montana
Number of Observations: 110

(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)

The Eastern Red Bat is migratory; all verified records in Montana (n = 11) are from the autumn migration period (between 2 August and 5 September); as of 2011 all individuals identified to sex (n = 3) were female.

The Eastern Red Bat migrates through eastern Montana, particularly along wooded and riparian areas. In other parts of its range, it is reported to prefer elm, box elder, wild plum, willow, hawthorn, sumac, and a variety of other woody plants for roosting, and hibernates in woodpecker holes, tree foliage, and under loose bark (Shump and Shump 1982a, Jones et al. 1983, van Zyll de Jong 1985).
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
No diet information is available from Montana. Elsewhere it is reported that Eastern Red Bat feeds on flying insects in wooded areas, often on moths (Lepidoptera) but also the Orders Homoptera, Coleoptera, Hymenoptera, and Diptera; they also feed on ground-dwelling crickets, flies, bugs, beetles, cicadas and grain moths (Shump and Shump 1982a). East of Montana they are reported to hunt around city street lights or barn flood lights.

No information from Montana. Elsewhere, these bats tend to be solitary, roosting singly or in female-litter groups, usually in foliage or tree cavities (1 to 6 m above ground but also at ground level) near habitat edges or water. Tends not to associate with other bat species, including foliage-roosting species, except during foraging or drinking. They often begin to forage within two hours after sunset, with some feeding throughout the night. During winter they arouse from hibernation on warm days to feed. Several species of mammals and raptorial birds are documented predators of Eastern Red Bat. In the east, Blue Jays are significant predators of young (Shump and Shump 1982a, Adams 2003).

Reproductive Characteristics
Little information available from Montana; two females caught on 9 and 11 August were nulliparous. Mating probably occurs during autumn migration and within the winter range, during August and September, but implantation delayed until spring. Gestation period is 80-90 days, young are born in late June and July, lactating females reported in southern Michigan in early August. Litter size ranges from 1-5, but averages about 3 (Shump and Shump 1982a).

No management measures have been enacted specifically for the protection of Eastern Red Bat in Montana, in part because we have too few data; more surveys are necessary to define habitat needs, dates of occurrence and migration, and population status. In Michigan, numbers captured in paired netting surveys have declined 52-85% over 1-26 years, which corresponds to a 10-fold reduction in numbers tested for rabies during 38 years (Winhold at el. 2008). Population declines, if real, could be related to forest fragmentation, pesticides and environmental pollutants, controlled burning of leaf litter, and collisions with various man-made objects, all of which could expose the species to hazards throughout the year. This species is also vulnerable to collision with wind turbines, and large numbers are killed at wind farms (Hendricks et al 2003, Arnett et al. 2008). 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.
    • Hendricks, Paul, C. Currier, S. Lenard, and J. Johnson. August/September 2003. MTNHP Bat Survey Field Form - Sites in central and southern Montana.
    • L. Winhold., A. Kurta, R. Foster. 2008. Long-term change in an assemblage of North American bats: are eastern red bats declining. Acta Chiropterologica 359-366
    • Shump, K.A., Jr. and A.U. Shump. 1982. (Lasiurus borealis). American Society of Mammalogists, Lawrence, KS. Mammalian Species No. 183:1-6.
    • Van Zyll de Jong, C.G. 1985. Handbook of Canadian mammals. Volume 2. Bats. National Museums of Canada, Ottawa. 212 pp.
  • Additional ReferencesLegend:   View Online Publication
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    • Foresman, K.R. 2001. The wild mammals of Montana. American Society of Mammologists, Special Publication Number 12. Lawrence, KS. 278 pp.
    • Reid, F. 2006. Peterson Field Guide to Mammals of North America, 4th Edition. Houghton Mifflin Company: Boston and New York, 608 pp.
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Citation for data on this website:
Eastern Red Bat — Lasiurus borealis.  Montana Field Guide.  Montana Natural Heritage Program and Montana Fish, Wildlife and Parks.  Retrieved on May 25, 2016, from