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Montana Field Guides

Least Weasel - Mustela nivalis

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Global Rank: G5
State Rank: S4

Agency Status
USFWS:
USFS:
BLM:
FWP Conservation Tier: 2


 

External Links





 
General Description
The smallest weasel and smallest carnivore in North America. Similar to other weasels in color and body form. Males are larger than females. Fur is brown above and whitish below during summer. Entirely white during winter. No black tip at end of short tail. Total length: less than 10 inches. Weight: one to three ounces.

Diagnostic Characteristics
Much smaller than the Short- or Long-tailed Weasel. Both Short- and Long-tailed Weasels have black tip on tail.

Species Range
Montana Range

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Western Hemisphere Range

 


Summary of Observations Submitted for Montana
Number of Observations: 57

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

Recency

 

(Records associated with a range of dates are excluded from time charts)



Migration
Non-migratory.

Habitat
Variety of habitats, including meadows, fields, brushy areas, and open woods. Avoids dense forest, prefers ecotones. Abundance of small mammals is important in determining the local distribution of Least Weasels. Marshy areas, meadows, cultivated fields, brushy areas and open woods (Svendsen 1982). Nest in shallow burrow about 5 inches underground (Jones et al. 1983).

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 bmaxell@mt.gov 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: http://mtnhp.org/requests/default.asp) 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
Feeds almost entirely on mice. Small enough to pursue rodents into runways, burrows, and nest chambers. Small rodents (voles) and rabbits. Males twice as large as females, and are able to shift to the larger prey (rabbits and Water Voles). Smaller females are better able to exploit small rodent burrows (Svendsen 1982).

Ecology
Size of home ranges may increase when small rodents are scarce. Population densities fluctuate in response to changes in small mammal abundances (Svendsen 1982).

Reproductive Characteristics
Breeds year-round, young born any time of the year. Delayed implantation does not occur. Litter size 3 to 9, but usually four to five. Both male and female reproductively mature at 3 to 4 months. Males may not breed until 10 months old. Gestation 35 days. Two to three litters per year (Svendsen 1982).

References
  • Additional ReferencesLegend:   View WorldCat Record   View Online Publication
    Do you know of a citation we're missing?
    • Beak Consultants, Inc., Portland, OR., 1983, Wildlife. January 1983. In Stillwater Project Environmental Studies. Addendum A, Wildlife. Vol. I. Tech. Report No. 7. 1982.
    • Chapman, J. A., and G. A. Feldhamer, editors. 1982. Wild mammals of North America: biology, management, and economics. Johns Hopkins University Press, Baltimore, Maryland.
    • Cross, James, and Richard P. Weckwerth, 1977, Upland Game Bird (and Fur Survey) Inventory. Wildlife Investigations, Region One. W-130- R-8, Job No. II-1, July 1, 1976 - June 30, 1977.
    • Cross, James, and Richard P. Weckwerth, 1978, Upland Game Bird (and Fur Survey) Inventory. Wildlife Investigations, Region One. W-130- R-9, Job No. II-1, July 1, 1977 - June 30, 1978.
    • Cross, James, and Richard P. Weckwerth, 1980, Upland Game Bird (and Fur Survey) Inventory. Wildlife Investigations, Region One. W-130- R-11, Job No. II-1, July 1, 1979 - June 30, 1980.
    • Cross, James, and Richard P. Weckwerth, 1981, Upland Game Bird (and Fur Survey) Inventory. Wildlife Investigations, Region One. W-130- R-12, Job No. II-1, July 1, 1980 - June 30, 1981.
    • Cross, James, and Richard P. Weckwerth, 1983, Upland Game Bird (and Fur Survey) Inventory. Wildlife Investigations, Region One. W-130- R-14, Job No. II-1, July 1, 1982 - June 30, 1983.
    • Erlinger, S. 1974. Distribution, territoriality, and numbers of the weasel MUSTELA NIVALIS in relation to prey abundance. Oikos 25(3):308-314.
    • Foresman, K. R. 2001. The wild mammals of Montana. American Society of Mammologists, Special Publication Number 12. Lawrence, KS. 278 p.
    • Hoffmann, R. S. and D. L. Pattie. 1968. A guide to Montana mammals: identification, habitat, distribution, and abundance. University of Montana, Missoula. 133 p.
    • http://mdt.mt.gov/research/docs/research_proj/animal_use/april_report.pdf
    • http://mdt.mt.gov/research/docs/research_proj/animal_use/interim_report_nov02.pdf
    • http://mdt.mt.gov/research/docs/research_proj/animal_use/progress_apr03.pdf
    • King, C. M. 1989. The natural history of weasels and stoats. Comstock Pub. Assoc. Ithaca, NY. 253 pp.
    • Lechleitner, R. R. 1954. Least weasel in Glacier National Park. J. Mammal. 35:594.
    • Montana Prairie Dog Working Group. 2002. Conservation plan for black-tailed and white-tailed prairie dogs in Montana. Montana Fish, Wildlife and Parks. Helena MT. 51 p.
    • Reid, F. 2006. Peterson Field Guide to Mammals of North America, 4th Edition. Houghton Mifflin Company: Boston and New York, 608 pp.
    • Sheffield, S. R. and C. M. King. 1994. Mustela nivalis. Mamm. Species 454:1-10.
    • Stearns-Roger Inc., 1975, Environmental baseline information of the Mount Vernon Region, Montana. January 31, 1975.
    • Stromberg, M. R. 1981. New record of the least weasel in Wyoming. Prairie Nat. 13(2):45-46.
    • Thompson, L.S. 1982. Distribution of Montana amphibians, reptiles, and mammals. Bozeman: Montana Audubon Council. 24 pp.
    • Zackheim, Karen, 1973?, Exhibit H: Wildlife Study. In Ash Grove Cement Co. files.
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Citation for data on this website:
Least Weasel — Mustela nivalis.  Montana Field Guide.  Montana Natural Heritage Program and Montana Fish, Wildlife and Parks.  Retrieved on December 22, 2014, from http://FieldGuide.mt.gov/speciesDetail.aspx?elcode=AMAJF02020
 
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