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Montana Field Guide

Montana Field Guides

Arctic Shrew - Sorex arcticus

Species of Concern

Global Rank: G5
State Rank: S1S3

Agency Status


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General Description
The Arctic Shrew is a medium to large sized shrew. Adults possess a distinctive tri-colored pelage; the dorsum is very dark brown to black, the sides are lighter brown, and the underparts are grayish-brown. The tail is distinctly bicolored, darker above and lighter below. Ranges in external measurements (in millimeters) are: total length 100 to 125, tail length 36 to 45, hind foot 12 to 15, and a mass of 5.3 to 13.5 grams. Condylobasal length of the skull is 19.0 to 20.0 millimeters, palatal length is 8.1 to 8.7 millimeters, maxillary breadth is 4.8 to 5.5 millimeters, and the length of the maxillary tooth row is 6.7 to 7.9 millimeters (Junge and Hoffmann 1981, Van Zyll de Jong 1983, Kirkland and Schmidt 1996). The skull has 32 teeth (dental formula: I 3/1, C 1/1, P 3/1, M 3/3); the 5 upper teeth with single cusps that are posterior to the first incisor are termed the unicuspids (U), and include 2 incisors, 1 canine, and 2 premolars. There is a medial tine on I1, and U3 is as large or larger than U4. On the lower jaw (mandible), the pigment is in two or three segments on I1 (the posterior extent of pigment on the ventromedial edge is restricted to about the first third), the height of the coronoid process is more than 4.3 millimeters, and the length of the dentary is greater than 7.8 millimeters (Carraway 1995).

Diagnostic Characteristics
Throughout its range, the Arctic Shrew is the only member of the subgenus Sorex, and is distinguished by its well-developed postmandibular canals and lack of pigmented ridges on the unicuspids (Junge and Hoffmann 1981, Kirkland and Schmidt 1996). In northeastern Montana, no other Sorex shrew is as large in skull or body measurements as the Arctic Shrew; the tricolored pelage is also distinctive.

Species Range
Montana Range

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Western Hemisphere Range


Summary of Observations Submitted for Montana
Number of Observations: 5

(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)

No information is available on movements.

Few descriptions of habitat use by Arctic shrew in Montana are available . All individuals have been captured in wet meadow habitat adjacent to marshes or in the sandy flats of creek flood plains. Dominant plants included Agropyron repens, Sonchus spp., Juncus balticus, Carex spp., Agropyron smithii, Distichlis spicata; Hordeum jubatum was also present (Perry 2000, Foresman 2012).

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: 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
Generally, Arctic Shrews feed largely on insects; the diet includes moth larvae, grasshoppers, larval and adult beetles, fly larvae, aquatic insects, and other terrestrial invertebrates (Jones et al. 1983, Kirkland and Schmidt 1996). Destructive larch sawfly larvae seasonally constitute a large part of its diet (Buckner 1964). The diet in Montana has not been reported or studied.

No studies have been completed for Arctic Shrew in Montana. Studies from other areas of the species' range reveal Arctic Shrews are active throughout the year, and are most often nocturnal (Baird et al. 1983, Kirkland and Schmidt 1996). All Montana captures have occurred in late July (Perry 2000, Foresman 2012). Other small mammal associates of Arctic Shrew across its range include the shrews Sorex cinereus, S. hoyi, and S. palustris (Wrigley et al. 1979, Kirkland and Schmidt 1996); S. cinereus has been captured in sympatry with the Arctic Shrew in Montana (Perry 2000, Foresman 2012).

Vital statistics, measures of population trends, and estimates of population density are rarely available. Home range size in Manitoba was 5913 square meters (Buckner 1966). Population density in Manitoba tamarack bogs was 4.1 to 5.1 per hectare in July and 7.3 to 7.8 per hectare in September; in Wisconsin marsh habitat, density was 8.6 per hectare (Kirkland and Schmidt 1996). There is high population turnover, with loss of approximately 80% of each generation prior to sexual maturity (Buckner 1966). Predators are largely unreported, but include the Great Horned Owl and weasels (Jones et al. 1983, Schowalter et al. 2002). Non-human predators in Montana are not known.

Reproductive Characteristics
No reproductive studies or data are available for Arctic Shrew in Montana. Studies from other areas of the species' range indicate this species' reproductive season extends from February to August in Wisconsin, and April to September in Minnesota. Gestation lasts 2 to 3 weeks, with a lactation period an additional 3.0 to 3.5 weeks. Litter size is 4 to 9, with an average of 2 litters (1 to 3) produced per year; a few females breed in consecutive years. Young-of-the-year sometimes breed late in the first summer in Minnesota. Mortality of nestling Arctic Shrews in the first month of life is estimated to be 50% or more, and 80% of cohort mortality occurs before sexual maturity is reached. Longevity may reach 18 months; adults surviving through the winter are not present in samples after July (Baird et al. 1983, Kirkland and Schmidt 1996).

No management needs are identified nor have any measures been enacted for the conservation of Arctic Shrew in Montana; the only occurrence so far known is on a National Wildlife Refuge. Nevertheless, wetland drainage or alteration has the potential to negatively impact local populations. Additional surveys for Arctic Shrew can provide the basis for development of conservation protocols by determining its full distribution in Montana, the array of habitats in which it occurs, its relative abundance in different habitats, and, if properly designed, an idea of how different habitat disturbances affect this shrew at the margin of its global range.

  • Literature Cited AboveLegend:   View Online Publication
    • Baird, D. D., R. M. Timm, and G. E. Nordquist. 1983. Reproduction in the arctic shrew, Sorex arcticus. Journal of Mammalogy 64:298-301.
    • Buckner, C.H. 1964. Metabolism, food capacity and feeding behavior in four species of shrews. Canadian Journal of Zoology 42: 259-79.
    • Buckner, C.H. 1966. Populations and ecological relationships of shrews in tamarack bogs of southeastern Manitoba. Journal of Mammalogy 47(2):181-194.
    • Carraway, L.N. 1995. A key to recent Soricidae of the western United States and Canada based primarily on dentaries. Occasional Papers of the Natural History Museum, University of Kansas (175):1-49.
    • Foresman, K.R. 2012. Mammals of Montana. Second edition. Mountain Press Publishing, Missoula, Montana. 429 pp.
    • Jones, J.K., D.M. Armstrong, R.S. Hoffmann and C. Jones. 1983. Mammals of the northern Great Plains. University of Nebraska Press, Lincoln. 379 pp.
    • Junge, J.A. and R.S. Hoffmann. 1981. An annotated key to the long-tailed shrews (genus Sorex) of the United States and Canada, with notes on middle American Sorex. Occasional Papers of the Museum of Natural History, the University of Kansas 94: 1-48.
    • Kirkland, G. L. and D. F. Schmidt. 1996. Sorex arcticus. American Society of Mammalogists, Lawrence, KS. Mammalian Species No. 524:1-5.
    • Perry, N. 2000. Baseline inventory of small mammals at Medicine Lake National Wildlife Refuge. Unpublished report to Medicine Lake National Wildlife Refuge, Medicine Lake, Montana. 10 pp.
    • Schowalter, D. B., L. Engley, and R. Digby. 2002. Records of Alberta small mammals through analyses of great horned owl pellets. Blue Jay 60:153-169.
    • Van Zyll de Jong, C.G. 1983. Handbook of Canadian mammals. 1. Marsupials and insectivores. National Museum of Natural Sciences, National Museums of Canada, Ottawa, Canada. 210 pp.
    • Wrigley, R.F., J.E. DuBois, and H.W. Copland. 1979. Habitat, abundance and distribution of six species of shrews in Manitoba. Journal of Mammalogy 60:505-520.
  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Foresman, K.R. 2001. The wild mammals of Montana. American Society of Mammalogists, Special Publication Number 12. Lawrence, KS. 278 pp.
    • George, S.B. 1988. Systematics, historical biogeography, and evolution of the genus Sorex Journal of Mammalogy 69:443-461.
    • Hoffmann, R.S. and D.L. Pattie. 1968. A guide to Montana mammals: identification, habitat, distribution, and abundance. University of Montana, Missoula. 133 pp.
    • Jones, J. K., Jr., R. S. Hoffman, D. W. Rice, C. Jones, R. J. Baker, and M. D. Engstrom. 1992. Revised checklist of North American mammals north of Mexico, 1991. Occasional Papers, The Museum, Texas Tech University, 146:1-23.
    • Junge, J.A., R.S. Hoffman, and R.W. DeBry. 1983. Relationships within the Holarctic Sorex arcticus-Sorex tundrensis species complex. Acta Theriologica 28:339-350.
    • Rausch, V.R., and R.L. Rausch. 1993. Karyotypic characteristics of Sorex tundrensis Merriam (Mammalia: Soricidae), a Nearctic species of the S. Araneus-group. Proceedings of the Biological Society of Washington 106:410-416.
    • Reid, F. 2006. Peterson Field Guide to Mammals of North America, 4th Edition. Houghton Mifflin Company: Boston and New York, 608 pp.
    • Volobouev, V.T. and C.G. Van Zyll de Jong. 1988. The karyotype of Sorex arcticus maritimensis (Insectivora, Soricidae) and its systematic implications. Canadian Journal of Zoology 66:1968-1972.
    • Youngman, P. M. 1975. Mammals of the Yukon Territory. Publications in Zoology, No. 10., National Museums of Canada, Ottawa. 192 pp.
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Arctic Shrew — Sorex arcticus.  Montana Field Guide.  .  Retrieved on , from