Pygmy Shrew - Sorex hoyi
Species of Concern
Global Rank:
G5
State Rank:
S3
Agency Status
USFWS:
USFS:
BLM:
FWP Conservation Tier:
2
External Links
General Description
The Pygmy Shrew is a relatively small member of the shrew family. The upperparts in summer are reddish-brown or grayish-brown, becoming paler on the flanks (especially in winter), with whitish, grayish, or rusty-gray underparts. In winter the pelage is brighter, drab above, and paler below. Ranges in external measurements (in millimeters) are: total length 67 to 98, tail length 25 to 34, hind foot 8.5 to 11.5, and a mass of 2.2 to 6.6 grams. Condylobasal length of the skull is 13.4 to 15.8 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 has a lengthy tine; U3 and U5 are small (U3 disc-like), easily overlooked upon superficial examination, and make it appear as though there are only three unicuspids. On the lower jaw, the length of the dentary is usually less than 6.1 millimeters, I1 is set at an angle more than 10 degrees from the horizontal ramus of the dentary, the length of C1-M3 is less than 4.2 millimeters, and the height of the coronoid process is usually 3.1 to 3.4 millimeters (Long 1974, Diersing 1980, Junge and Hoffmann 1981, Carraway 1995).
Diagnostic Characteristics
Pygmy Shrew can be distinguished from all other North American Sorex by its small disc-like U3 and the long medial tine on I1 (Junge and Hoffmann 1981). Upon superficial examination, there appear to be only 3 upper unicuspid teeth, instead of 4 to 5. The combination of lower jaw traits (length of the dentary usually less than 6.1 millimeters, I1 set at an angle more than 10 degrees from the horizontal ramus of the dentary, length of C1-M3 less than 4.2 millimeters, height of the coronoid process usually 3.1 to 3.4 millimeters) distinguishes Sorex hoyi from sympatric S. haydeni, S. preblei, and S. merriami using only dentaries (Carraway 1995).
General Distribution
Summary of Observations Submitted for Montana
Number of Observations: 25
(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
No information is available on movements in Montana. Based upon information from other locations, the species is generally considered non-migratory; apparently only local movements are made.
Habitat
Dry, open coniferous forests (ponderosa pine, western larch) appear to be preferred by Pygmy Shrews in Montana. Individuals have also been captured in mesic Douglas-fir-lodgepole pine forests, and sagebrush-steppe in northern Beaverhead County (Foresman 1999, 2001). Understory plants include Amelanchier alnifolia, Berberis repens, Arnica cordifolia, Symphoricarpos occidentalis, Ribes spp., Equisetum spp., and Carex spp. The skull recovered in Hill County (Jean and Hendricks 2001, Hendricks 2001) was found in an area largely of open prairie vegetation (Bouteloua gracilis, Koeleria macrantha, Poa secunda, Stipa comata, Carex filifolia, Pascopyrum smithii) but may have originated in one of the forested uplands nearby. However, a specimen was captured in similar prairie habitat in the pothole region of Sheridan County (D. Flath personal communication).
Throughout its range, the Pygmy Shrew is found in a variety of habitats. It appears to prefer grassy openings in boreal forest, with moist habitats preferred over dry areas. In Kentucky and Tennessee, it was much less active above ground than the Southeastern Shrew (S. longirostris) (Feldhamer et al. 1993). Nest sites are not well known. Habitat associations in Manitoba, Wisconsin and Minnesota include mesic forests of hemlock, white pine, aspen, black spruce-tamarack, maple, jack pine, and sometimes in marshy areas (Long 1972, 1974, Wrigley et al. 1979). In eastern South Dakota an individual was captured in cattail-rush habitat on the edge of a slough (Jones et al. 1983). It has been captured in mesic grand fir-subalpine fir-Engelmann spruce forest in the panhandle of Idaho, and ponderosa pine-lodgepole pine-Douglas-fir forest in northeastern Washington (Stinson and Reichel 1985, Foresman 1986). Farther south, in southern Wyoming and northern Colorado, it is associated with bogs and moist spruce-fir forest meadows (Brown 1966, 1967, Armstrong 1972, Clark and Stromberg 1987).
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:
- 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);
- 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 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 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.
- Commonly Associated with these Ecological Systems
Forest and Woodland Systems
Grassland Systems
Open Water / Wetland and Riparian Systems
Shrubland, Steppe and Savanna Systems
- Occasionally Associated with these Ecological Systems
Grassland Systems
Food Habits
Pygmy Shrews appear to prey primarily on invertebrates, although there are few studies of the food habits. Examination of stomach contents revealed larval Lepidoptera, larval and adult Coleoptera, larval and adult Diptera, earthworms, snails, and slugs (Jones et al. 1983). The diet in New Brunswick included mainly insect larvae, beetles, and spiders (Whitaker and French 1984). Captives have fed on meat (mice), fish, grasshoppers, and other insects. The diet in Montana has not been reported or studied.
Ecology
Pygmy Shrew is active throughout the year, with records from all months (Brown 1966, Long 1972, Stinson and Reichel 1985, Foresman 1986, Feldhamer et al. 1993). Records in Montana are mostly from June to August, with early October the latest (Koford 1938, Setzer 1952, Hoffmann et al. 1969, D. Flath personal communication).
The Pygmy Shrew is not expected to occur in high densities (van Zyll de Jong 1983). Other small mammal associates of Pygmy Shrew across its range include the shrews Sorex arcticus, S. cinereus, S. fumeus, S. longirostris, S. monticolus, S. vagrans (Brown 1967, Long 1972, Foresman 1986, Feldhamer et al. 1993); it is often reported associated with Southern Red-backed Voles (Clethrionomys gapperi). In Montana, Pygmy Shrew has been found associated with the shrews S. cinereus, S. monticolus, and S. vagrans, as well as the vole Clethrionomys gapperi (Foresman 1999).
Vital statistics, measures of population trends, and estimates of population density are usually not available. In Michigan, densities of 0.1 to 1.9 individuals per hectare were estimated (Baker 1983, Smallwood and Smith 2001). Pygmy Shrew appears to be relatively common locally at some sites (Hoffmann et al. 1969, Foresman 1999), but is considered uncommon across large landscapes. Reported predators include gartersnakes, domestic cats, and hawks (Buteo). The only non-human predator of Pygmy Shrew reported in Montana is an unidentified species of raptor (Hendricks 2001).
Reproductive Characteristics
No study of the reproductive biology of Pygmy Shrew in Montana is available. Specimen data indicate litters are produced in spring and early summer, and parous females (pregnant or lactating) have been captured in early August. Recorded litter sizes are 3 to 6 (Hoffmann et al. 1969, Long 1974, Foresman 1999, 2001).
Pregnant and lactating females have been captured in July in Wisconsin; August captures included lactating females as well as young-of-the-year. Records from Wyoming and Colorado in July and August include pregnant or lactating females as well as juveniles (Long 1972, 1974); thus in the West and upper Midwest, parturition appears to occur in spring and summer. Conversely, in Kentucky and Tennessee the primary period young are born is November to early March, with fewest births during April to July (Feldhamer et al. 1993); individuals entered the trappable population about 8 weeks later. Gestation lasts probably 2 to 3 weeks. Litter size is 3 to 8. There is little evidence that more than one litter per year is produced; an Idaho female with mature mammary glands was also in early pregnancy, indicating previous suckling of a litter or a lost litter with subsequent rebreeding (Foresman 1986). Sexual maturity in the West is probably reached late in the first year. Longevity is reportedly 14 to 16 months; only about 9.7% of individuals in a Kentucky-Tennessee study were more than 1 year old, with the oldest individuals about 17.5 months (Feldhamer et al. 1993) and probably surviving through two winters.
Management
No management measures have been enacted for pygmy shrew in Montana. It appears to be relatively common locally at some sites (Hoffmann et al. 1969, Foresman 1999), but is considered uncommon across large landscapes. Its occurrence in Swan Valley timberlands harvested 1 to 3 years prior may indicate tolerance to a moderate level of disturbance, although this, and response to other kinds of disturbance, needs more study.
Additional surveys for pygmy 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
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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. 54pp.- Armstrong, D. M. 1972. Distribution of mammals in Colorado. University of Kansas Museum of Natural History Monograph 3:26-31.
- Baker, R. H. 1983. Michigan mammals. Michigan State University Press. 642 pp.
- Boggs, Keith., , Field inventory of wildlife resources . . . WICHE Proj. No. D117. Spec. Oc./Habitat Type.
- Brown, L. N. 1966. First record of the Pigmy Shrew in Wyoming and description of a new subspecies (Mammalia: Insectivora). Proceedings of the Biological Society of Washington 79:49-52.
- Brown, L.N. 1967. Ecological distribution of six species of shrews and comparison of sampling methods in the central Rocky Mountains. J. Mammal. 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.
- Dierseing, V.E. 1980. Systematics and evolution of the pygmy shrews (subgenus Microsorex) of North America. J. Mamm. 61(1): 76-101.
- Feldhamer, G. A., et al. 1993. Habitat partitioning, body size, and timing of parturition in pygmy shrews and associated soricids. J. Mamm. 74:403-411.
- Flath, Dennis L., 1979, Nongame species of special interest or concern: Mammals, birds, reptiles, amphibians, fishes. January 1979.
- Foresman, K. R. 1986. Sorex hoyi in Idaho: a new state record. Murrelet 67:81-82.
- Foresman, K. R. 1999. Distribution of the Pygmy Shrew, Sorex hoyi, in Montana and Idaho. Canadian Field-Naturalist 113:681-683.
- Foresman, K. R. 2001. The Wild Mammals of Montana. American Society of Mammologists, Special Publication No. 12: Lawrence, KS, 278 pp.
- George, S. B. 1988. Systematics, historical biogeography, and evolution of the genus SOREX. J. Mammalogy 69:443-461.
- Hendricks, P. 2001. A significant new record of the Pygmy Shrew, Sorex hoyi, on the Montana-Alberta border. Canadian Field-Naturalist 115:513-514.
- Hoffmann, R. S. and D. L. Pattie. 1968. A guide to Montana mammals: identification, habitat, distribution, and abundance. Univ. Mont., Missoula. 133 pp.
- Hoffmann, R.S., P.L. Wright, and F.E. Newby. 1969. Distribution of some mammals in Montana. I. Mammals other than bats. J. Mammal. 50(3): 579-604.
- Jean, C., and P. Hendricks. 2001. Lund easement baseline biological inventory. Report to the Natural Resource Conservation Service. Montana Natural Heritage Program, Helena, Montana. 15 pp. plus appendices.
- Jones, J. K. Jr., D. M. Armstrong, R. S. Hoffmann and C. Jones. 1983. Mammals of the northern Great Plains. Univ. Neb. 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. Occ. Pap. Mus. Nat. Hist. Univ. Kansas. 94: 1-48.
- Long, C. A. 1972. Notes on habitat preferences and reproduction in pygmy shrews (Microsorex hoyi). Can. Field Nat. 86:155-160.
- Long, C. A. 1974. Sorex hoyi. American Society of Mammalogists, Lawrence, KS. Mammalian Species No. 33:1-4.
- Long, C. A. 1974. MiCROSOREX HOYI and MIRCOSOREX THOMPSONI. Mamm. Species 33:1-4.
- Mengak, Micheal T., et. al. 1987. Abundance and distribution of shrews in western South Carolina. Brimleyana (13):63-66.
- Reid, F. 2006. Peterson Field Guide to Mammals of North America, 4th Edition. Houghton Mifflin Company: Boston and New York, 608 pp.
- Setzer, H. W. 1952. Pigmy Shrew, Microsorex, in Montana. Journal of Mammalogy 33:398.
- Smallwood, K. Shawn, and T. R. Smith. 2001. Study design and interpretation of shrew (Sorex) density estimates. Annales Zoologici Fennici 38:149-161.
- Spencer, A. W. and D. Pettus. 1966. Habitat preferences of five sympatric species of long-tailed shrews. Ecology 47: 677-683.
- Stinson, D. W., and J. D. Reichel. 1985. Rediscovery of the Pygmy Shrew in Washington. Murrelet 66:59-60.
- van Zyll de Jong, C. G. 1976. Are there two species of Pygmy Shrews (Microsorex)? Canadian Field-Naturalist 90:485-487.
- Whitaker, J. O., Jr., and T. W. French. 1984. Foods of sixspecies of sympatric shrews from New Brunswick. Can. J. Zool. 62:622-626.
- Wrigley, R.F., J.E. DuBois, and H.W. Copland. 1979. Habitat, abundance and distribution of six species of shrewsin Manitoba. J. Mamm. 60:505-520.
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