Muskrat - Ondatra zibethicus
(see State Rank Reason below)
State Rank Reason (see State Rank above)
Species is relatively common within suitable habitat and widely distributed across portions of the state
- Details on Status Ranking and Review
ScoreG - 200,000-2,500,000 km squared (about 80,000-1,000,000 square miles)
Comment380,531 square Kilometers from Natural Heritage Program range maps
ScoreE - Relatively Stable (±25% change)
CommentHabitat is likely stable within +/- 25% since European settlement
ScoreU - Unknown. Short-term trend in population, range, area occupied, and number and condition of occurrences unknown.
CommentNo data on trends available
ScoreH - Unthreatened. Threats if any, when considered in comparison with natural fluctuation and change, are minimal or very localized, not leading to significant loss or degradation of populations or area even over a few decades’ time. (Severity, scope, and/or immediacy of threat considered Insignificant.)
CommentNo operational threats in the next 15-20 years identified
ScoreC - Not Intrinsically Vulnerable. Species matures quickly, reproduces frequently, and/or has high fecundity such that populations recover quickly (< 5 years or 2 generations) from decreases in abundance; or species has high dispersal capability such that extirpated populations soon become reestablished through natural recolonization (unaided by humans).
CommentNot Intrinsically Vulnerable. Species matures quickly, reproduces frequently, and/or has a high fecundity such that populations recover quickly (< 5 years or 2 generations) from decreases in abundance. Species has good dispersal capabilities such that e
ScoreD - Broad. Generalist. Broad-scale or diverse (general) habitat(s) or abiotic and/or biotic factors are used or required by the species, with all key requirements common in the generalized range of the species in the area of interest. If the preferred food(s) or breeding/nonbreeding microhabitat(s) become unavailable, the species switches to an alternative with no resulting decline in numbers of individuals or number of breeding attempts.
CommentFound in lentic and lotic waterbodies across a diversity habitats
Raw Conservation Status Score
3.5 + 0 (geographic distribution) + 0.5 (environmental specificity) + 0 (long-term trend) + 1 (threats) = 5
Muskrats are large voles adapted to aquatic conditions. The name "Muskrat" is related to odoriferous secretions from the perineal glands. The long naked tail flattened laterally distinguishes Muskrats from other mammals. Webbed hind feet. Fur is dense and rich brown with a coarse guard hair overlay and thick waterproof under-layer. Color varies from dark brown to black. Total length: 16 to 26 inches. Weight: two to four pounds. Most active at night but daytime activity is not unusual. Often builds conspicuous dome-shaped houses.
Beaver has large dorsally flattened scale over tail.
Western Hemisphere Range
Observations in Montana Natural Heritage Program Database
Number of Observations:
(Click on the following maps and charts to see full sized version)
Map Help and Descriptions
(Observations spanning multiple months or years are excluded from time charts)
The most widespread of North American microtine (a subfamily of mice) rodents. Marshes, edges of ponds, lakes, streams, cattails, and rushes are typical habitats. An essential habitat ingredient is water of sufficient depth or velocity to prevent freezing. The presence of herbaceous vegetation, both aquatic and terrestrial, is another essential ingredient. In general, has very flexible habitat requirements and often coexists in habitats used by Beavers. Lentic or slightly lotic water containing vegetation. Typha spp. (cattails) and Scirpus spp. (bulrushes) usually present. Constructs bank dens, lodges, feeding huts, platforms, pushups and canals (Perry 1982).
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:
- 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);
- Evaluating structural characteristics and distribution of each ecological system relative to the species' range and habitat requirements;
- Examining the observation records for each species in the state-wide point observation database associated with each ecological system;
- 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: 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.
- Adams, R.A. 2003. Bats of the Rocky Mountain West; natural history, ecology, and conservation. Boulder, CO: University Press of Colorado. 289 p.
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Primarily herbivorous and will eat virtually any vegetable matter. Utilizes shoots, roots, bulbs, and leaves of aquatic plants. Cattails and bulrush are preferred foods. Will also consume cultivated crops. On occasion will eat animal matter. Food is stored in the burrow or den and during winter may even eat part of its own lodge.
Population is cyclic. Wetland habitats important. Over-populated wetlands may experience an eatout with both above ground and below ground emergent vegetation entirely consumed (Perry 1982).
Breeds during spring and summer. Five or six young are born after a 22- to 30-day gestation. May have two or three litters per year. Polyestrous, promiscuous or loosely monogamous. Breeding parameters vary by geographic area. Probably 1 to 3 litters/yr, 5 to 8 young/litter; probably breeds March to October with March to June peak period (Perry 1982).
- Literature Cited AboveLegend: View Online Publication
- Perry, H.R. 1982. Muskrats. Pp. 282-325 in: Chapman, J.A. and G.A. Feldhamer (eds). Wild mammals of North America. John Hopkins University Press, Baltimore. 1147 pp.
- Additional ReferencesLegend: View Online Publication
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- Additional Sources of Information Related to "Mammals"