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Montana Animal Field Guide

Montana Field Guides

Merriam's Shrew - Sorex merriami

Species of Concern

Global Rank: G4
State Rank: S3

Agency Status
USFWS:
USFS:
BLM:
FWP SWAP: SGCN3


 

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General Description
Merriam's Shrew is a relatively small, pale shrew. The upperparts in summer are grayish drab, becoming paler on the flanks, with nearly white underparts (faintly tinged with buff). In winter the pelage is brighter, drab above, and paler below. The tail is distinctly bicolored, sparsely haired, drab above, and white below. Ranges in external measurements (in millimeters) are: total length 88 to 107, tail length 33 to 42, hind foot 11 to 13, and mass 3.3 to 6.5 grams. Condylobasal length of the skull is 15.0 to 17.1 millimeters, and maxillary breadth is 4.9 to 5.6 millimeters. 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. The medial edge of the first incisor lacks a tine; U3 is as large or larger than U4 (Armstrong and Jones 1971, Junge and Hoffmann 1981, Verts and Carraway 1998, Foresman 2012).

Diagnostic Characteristics
Merriam's Shrew differs from other members of the genus in Montana by the combination of small size, pale coloration, lack of a medial tine on I1, broad palate (maxillary breadth more than 5.0 millimeters), and U3 as large or larger than U4. Habitat of occurrence, when used in conjunction with the preceding, is also useful for identifying this species (Junge and Hoffmann 1981, Mullican and Carraway 1990). A key based on dentaries identifies the unique characteristics for this species (Carraway 1995), including height of the coronoid process more than 3.9 millimeters, length of C1-M3 more than 4.3 millimeters, and length of dentary usually greater than 6.6 millimeters. These characters separate S. merriami from S. nanus, S. preblei, and S. hoyi, each of which may occur in sympatry.

Species Range
Montana Range

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Western Hemisphere Range

 


Summary of Observations Submitted for Montana
Number of Observations: 30

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

Recency

 

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



Migration
No information is available on movements in Montana. Generally the species is thought to be non-migratory; apparently only local movements are made.

Habitat
Merriam's Shrews in Montana have been captured mostly in arid sagebrush-grassland habitats (Hoffmann et al. 1969, Pefaur and Hoffmann 1971, MacCracken et al. 1985, Foresman 2012), but also in non-native grasses and forbs, such as timothy and sweet clover (Hooper 1944). It has also been taken in poorly developed riparian habitat at creekside in a shrub-steppe and grassland region (Dood 1980). Bare ground was more than 20% in a Carter County capture location (MacCracken et al. 1985); and on a north-facing grassland slope (elevation of 1040 meters) (Pefaur and Hoffmann 1971).

Across its range, Merriam's Shrew is identified as occupying arid Upper Sonoran and Lower Transition life zones. It has been captured in sagebrush-steppe, pine woodland, mountain mahogany, open ponderosa pine stands, spruce-aspen stands, forb-dominated mine-reclamation land, bunchgrass grassland, and dunes (Hudson and Bacon 1956, Brown 1967, Allred 1973, George 1990, Kirkland et al. 1997, Verts and Carraway 1998, Benedict et al. 1999, Nagorsen et al. 2001, Hafner and Stahlecker 2002). Merriam's Shrew seems to prefer drier habitats than do other shrews, and may also utilize burrows and runways of various microtines and other mice (Armstrong and Jones 1971). Shrub cover in British Columbia was as low as 5% (Nagorsen et al. 2001), and ranged from 28 to 71% in Idaho (Allred 1973), sometimes with 30% juniper cover.

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: 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.  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
Few studies report dietary information for Merriam's Shrew. In eastern Washington, analysis of Merriam's Shrew diet showed it feeds primarily on the ground on caterpillars (Lepidoptera), beetles (especially Carabidae and Tenebrionidae), crickets (Gryllidae, including Ceuthophilus spp.), ichneumonid wasps, and spiders (Johnson and Clanton 1954). It has the highest relative bite force of all western shrews studied, suggesting that it is adapted to forage on relatively large, hard-bodied prey (Verts and Carraway 1998). The diet in Montana has not been reported or studied.

Ecology
This shrew is not well described and little is known, particularly in Montana, though there are records in Montana from late March to late December. This shrew may be associated with Lagurus curtatus (Sagebrush Vole) runways (Jones 1983).

Based upon information gathered elsewhere, Merriam's Shrew has been captured in most months, showing it may be active year round (Johnson and Clanton 1954, Hudson and Bacon 1956), including when temperatures are as low as -6 degrees F (Benedict et al. 1999). Remains in owl pellets indicate it may be most active on the surface during night (most trap captures appear to occur at night), although it has been taken in pitfall traps in mid-morning (Johnson and Clanton 1954).

In Washington and Wyoming, Merriam's Shrew has frequently been found in association with the Sagebrush Vole (Lagurus curtatus). Other shrew species sympatric with Merriam's Shrew include Sorex cinereus, S. monticolus, S. nanus, and S. preblei (Johnson and Clanton 1954, Hudson and Bacon 1956, Kirkland et al. 1997, Benedict et al. 1999, Hafner and Stahlecker 2002). In southeastern Montana, Merriam's Shrew has been captured in association with S. nanus (MacCracken et al. 1985).

Remains of Merriam's Shrew have been found in owl pellets in California and Wyoming (Armstrong and Jones 1971); the only other predator reported is the domestic cat (Mullican 1986). The only non-human predator of Merriam's Shrew reported in Montana is the Great Horned Owl (Hoffmann et al. 1969).

Vital statistics, measures of population trends, and estimates of population density are not available. At many locations where other shrews are present, Merriam's Shrew is often one of the less common, nowhere appearing abundant, and requiring several hundred trap-nights of effort per individual captured (Hudson and Bacon 1956, Brown 1967, Kirkland et al. 1997, Verts and Carraway 1998, Nagorsen et al. 2001). However, in appropriate sites in New Mexico it may be relatively abundant (Hafner and Stahlecker 2002). Along the southern base of the Pryor Mountains in Carbon County in 1995, it was the only shrew species captured (9 in 1692 trap-nights; Paul Hendricks unpublished data), and in Carter County only one was captured in 14,400 trap-nights (MacCracken et al. 1985).

Reproductive Characteristics
The reproductive biology in Montana has not been studied.

In Washington, mating probably occurs between March and June, although multiple litters may be produced; pregnant females have been captured from late April to early July, and females with enlarged mammary glands in March, July and October. Size of three litters was 5, 6, and 7 (Johnson and Clanton 1954). In Nebraska, young of the year with no tooth wear were captured in May and early June, and adult males captured in late May and June had enlarged testes (Benedict et al. 1999). Males may also have a strong odor, especially during the breeding season (Jones 1983). Young-of-the-year with light tooth wear have also been captured in December, indicating that more than one litter is likely produced in Nebraska, as is probable in Washington. There are no reports on longevity in this species.

Management
No management measures have been enacted for Merriam's Shrew in Montana. However, alteration or removal of grassland and sagebrush through fire, herbicides, or mechanical methods, may impact local populations. Measures taken to protect a diversity of size and cover classes of grassland and sagebrush will likely contribute to the conservation of Merriam's Shrew. Surveys for Merriam's 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 rare shrew.

References
  • Literature Cited AboveLegend:   View Online Publication
    • Allred, D. M. 1973. Small mammals of the National Reactor Testing Station, Idaho. Great Basin Naturalist 33:246-250.
    • Armstrong, D. M. and J. Knox Jones, Jr. 1971. Sorex merriami. Mammalian Species 2:1-2.
    • Benedict, R. A., J. D. Druecker, and H. H. Genoways. 1999. New records and habitat information for Sorex merriami in Nebraska. Great Basin Naturalist 59:285-287.
    • Brown, L.N. 1967. Ecological distribution of six species of shrews and comparison of sampling methods in the central Rocky Mountains. Journal of Mammalogy 48(4): 617-623.
    • 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.
    • Dood, A.R. 1980. Terry Badlands nongame survey and inventory final report. Montana Department of Fish, Wildlife, and Parks and Bureau of Land Management, Helena, MT. 70 pp.
    • Foresman, K.R. 2012. Mammals of Montana. Second edition. Mountain Press Publishing, Missoula, Montana. 429 pp.
    • George, S. B. 1990. Unusual records of shrews in New Mexico. Southwestern Naturalist 35:464-465.
    • Hafner, D. J. and D. W. Stahlecker. 2002. Distribution of Merriam's shrew (Sorex merriami) and the dwarf shrew (Sorex nanus), and new records for New Mexico. Southwestern Naturalist 47:134-137.
    • Hooper, E.T. 1944. Additional records of Merriam's shrew in Montana. Journal of Mammalogy 25:92.
    • Hudson, G. E. and M. Bacon. 1956. New records of Sorex merriami for eastern Washington. Journal of Mammalogy 37(3):436-437.
    • Johnson, M. L. and C. W. Clanton. 1954. Natural history of Sorex merriami in Washington State. The Murrelet 35 (1): 1-4.
    • 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., Jr., R. R. Parmenter, and R. E. Skoog. 1997. A five-species assemblage of shrews from the sagebrush-steppe of Wyoming. Journal of Mammalogy 78:83-89.
    • MacCracken, J. G., D. W. Uresk, and R. M. Hansen. 1985. Habitat used by shrews in southeastern Montana. Northwest Science 59(1):24-27.
    • Mullican, T. R. and L. N. Carraway. 1990. Shrew remains from Moonshiner and Middle Butte caves, Idaho. Journal of Mammalogy 71:351-356.
    • Mullican, T.R. 1986. Additional records of Sorex merriami from Idaho. Murrelet 67:19-20.
    • Nagorsen, D. W., G. G. E. Scudder, D. J. Huggard, H. Stewart, and N. Panter. 2001. Merriam's shrew, Sorex merriami, and Preble's shrew, Sorex preblei: two new mammals for Canada. Canadian Field-Naturalist 115:1-8.
    • Pefaur, J.E. and R.S. Hoffmann. 1971. Merriam's shrew and hispid pocket mouse in Montana. American Midland Naturalist 86(1):247-248.
    • Verts, B. J. and L. N. Carraway. 1998. Land mammals of Oregon. University of California Press, Berkeley. xvi + 668 pp.
  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Allen, K.L., T. Weaver, and D. Flath. 1994. Small mammals in Northern Rocky Mountain ecosystems. Unpubl. report to Bureau of Land Management and United States Forest Service, August 31, 1994. Montana State Univ., Bozeman. 54 pp.
    • Bonnichsen, R., R. W. Graham, T. Geppert, J. S. Oliver, S. G. Oliver, D. Schnurrenberger, R. Stuckenrath, A. Tratebas, and D. E. Young. 1986. False cougar and shield trap caves, Pryor Mountains, Montana. National Geographic Research 2(3):276-290.
    • Confluence Consulting Inc. 2010. Montana Department of Transportation Wetland Mitigation Monitoring Reports (various sites). MDT Helena, MT.
    • Diersing, V.E. 1979 Noteworthy Records of Merriam's Shrew From New Mexico Southwest. Nat. 24(4):708-709.
    • Diersing, V.E. and D.F. Hoffmeister. 1977. Revision of the shrews Sorex merriama and a description of a new species of the subgenus Sorex. Journal of Mammalogy 58:321-333.
    • Flath, D.L. 1979. Nongame species of special interest or concern: Mammals, birds, reptiles, amphibians, fishes. Wildlife Division, Montana Department of Fish and Game. Helena, MT.
    • Foresman, K.R. 2001. The wild mammals of Montana. American Society of Mammalogists, Special Publication Number 12. Lawrence, KS. 278 pp.
    • Gashwiler, J.S. 1976. A New Distribution Record of Merriam's Shrew in Oregon. Murrelet. 57:13-14.
    • George, S.B. 1988. Systematics, historical biogeography, and evolution of the genus Sorex Journal of Mammalogy 69:443-461.
    • Geppert, T. J. 1984. Small mammals of the Shield Trap, East Pryor Mountain, Montana. M.S. thesis. University of Iowa, Iowa City. 45 pp.
    • Hoffmann, R.S. and D.L. Pattie. 1968. A guide to Montana mammals: identification, habitat, distribution, and abundance. University of Montana, Missoula. 133 pp.
    • Hoffmann, R.S., P.L. Wright, and F.E. Newby. 1969. The distribution of some mammals in Montana. I. Mammals other than bats. Journal of Mammalogy 50(3): 579-604.
    • Merriam, C. H. 1895. Synopsis of the American shrews of the genus Sorex. North American Fauna 10:57-98, 114-125.
    • Mickey, A.B. 1947. A record of Sorex merriami for southeastern Wyoming. Journal of Mammalogy. 28:293.
    • Ports, M. A. and S. B. George. 1990. Sorex preblei in the northern Great Basin. Great Basin Naturalist 50: 93-95.
    • Reid, F. 2006. Peterson Field Guide to Mammals of North America, 4th Edition. Houghton Mifflin Company: Boston and New York, 608 pp.
    • Roy F. Weston, Inc., Bozeman, MT., and Western Technology and Engineering, Inc., Helena, MT., 1989, Stillwater PGM Resources East Boulder Project Addendum F: Supplemental Biological Studies. Final Report. December 1989.
    • Thompson, L.S. 1982. Distribution of Montana amphibians, reptiles, and mammals. Bozeman: Montana Audubon Council. 24 pp.
    • Waage, Bruce C., 2001, Western Energy Company Rosebud Mine, Colstrip, Montana: 2000 Annual Wildlife Monitoring Report; December 1, 1999 - November 30, 2000. March 30, 2001.
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