Sorex fumeus Miller, 1895
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Basis for Listing
The smoky shrew occurs in the eastern United States from northern Georgia, throughout the Appalachian Mountain region, into the Maritimes Provinces of Canada, and westward to southern Ontario (Owen 1984). The presence of smoky shrews in extreme northeastern Minnesota was first documented in 1991 (Jannett and Oehlenschlager 1994) and subsequently further west in Lake County in 2003. Minnesota now represents the western edge of the species' distribution. Timm (1975) and Christian and Daniels (1985) conducted extensive studies of small mammals in Cook County, but failed to detect the presence of this Appalachian shrew in Minnesota. De Vos (1964) considered the smoky shrew a species that was extending its distribution westward in the Great Lakes Region, but it is unknown if the specimens reported represent a recent invasion of the species from the east, or rather, if it has long occupied the region in low, but previously undetected numbers. The species clearly is at the western margin of its distributional range in Minnesota, and must be considered uncommon based on the many years of study in the region without previous detection. For these reasons, the smoky shrew was listed as a special concern species in 1996.
The smoky shrew is a mouse-sized animal with a pointy nose, small eyes, and a long tail. It is relatively large for a shrew, weighing in at an average of 7.6 g (0.27 oz.) and measuring 101-127 mm (4-5 in.) in total length (Owen 1984; Whitaker 1999). The fur of adult smoky shrews is generally slate gray to black on the back and lighter to silvery on the belly. They may appear dull brown in the summer (Owen 1984). The young are born gray and will change to their adult color the following summer (Whitaker 1999). The tail of smoky shrews is dark on the top and lighter on the bottom and is generally thicker than that of other similar shrew species. Smoky shrews resemble masked shrews (Sorex cinereus), arctic shrews (Sorex arcticus), and water shrews (Sorex palustris). Masked shrews are smaller, have thinner tails, and have a browner fur color. Arctic shrews are about the same size as smoky shrews, but the arctic shrew's fur is generally tri-colored with dark brown fur on its back, lighter brown fur on its sides, and pale brown fur on its belly. The arctic shrew's fur pattern is less distinctive in young shrews, but young arctic shrews are smaller than smoky shrews. Water shrews are larger and have conspicuous fringes of stiff hair on their hind feet.
Throughout its range, smoky shrews occur in deciduous and coniferous forests, bogs, and swamps. Moist habitats are important (McShea et al. 2003) and the preferred microhabitat includes a cool, damp forest floor with a thick litter layer, mossy covered rocks, and decaying debris (Owen 1984). In Minnesota, smoky shrews have been found in glacial boulder streams; second-growth black spruce, fir, paper birch forests (Jannett and Oehlenschlager 1994); mossy, talus slopes; and sphagnum bogs.
Biology / Life History
Smokey shrews are active year round, and have been found to tolerate temperatures well below zero. They have a high metabolism and must eat up to half their body weight in food per day in order to survive. Unlike many other shrews, smoky shrews do not mate until after their first winter. They mate from March through September or October, and the females may have 2-3 litters per year. Gestation is estimated to last 3 weeks, after which females gives birth to 3-7 young inside a nest built out of shredded vegetation and other materials in a rock crevice, or under a log, stump, or rock (Whitaker 1999). The young will stay in the nest until they are nearly full grown (approximately 1 month).
Conservation / Management
The presence of smoky shrews is related to soil moisture and mesic habitats, with more individuals being found in larger (McShea et al. 2003), older patches of habitat (Kuttner and Malcolm 2001). Because of this and the fact that little is known about the species' ability to recolonize areas after logging, the potential presence of smoky shrews should be considered when mesic forests in the vicinity of documented occurrences of this species are slated for harvest.
Conservation Efforts in Minnesota
Very little is known about the ecology and population status of smoky shrews in Minnesota. The preferred habitat of the species is currently not uncommon in northern Minnesota, so it is possible that habitat is not a limiting factor for the species in the state. The Minnesota Biological Survey targeted smoky shrews in their 2003 survey, and documented six new locations, expanding the known range of the species in Minnesota west into Lake County. It is not known, however, if smoky shrews inhabited this area historically and simply remained undetected until recently. Future surveys are needed to determine the full extent of the species' distribution and population in the state.
Christian, D. P., and J. M. Daniels. 1985. Distributional records of Rock Voles, Microtus chrotorrhinus, in northeastern Minnesota. Canadian Field-Naturalist 99:356-359.
de Vos, A. 1964. Range changes of mammals in the Great Lakes Region. American Midland Naturalist 71:210-231.
Jannett, F. J., Jr., and R. J. Oehlenschlager. 1994. Range extension and first Minnesota records of the Smokey Shrew Sorex fumeus. American Midland Naturalist 131:364-365.
Kuttner, B. G., and J. R. Malcom. 2001. Small mammal responses to clearcut logging in northeastern Ontario. Abstract of presentation given at Symposium on Old-growth Forest in Canada, October 2001, Sault Ste. Marie, Ontario.
McShea, W. J., J. P. Pagels, J. Orrock, E. Harper, and K. Koy. 2003. Mesic deciduous forest as patches of small-mammal richness within an Appalachian mountain forest. Journal of Mammalogy 84:627-643.
Owen, J. G. 1984. Sorex fumeus. Mammalian Species 215:1-8.
Timm, R. M. 1975. Distribution, natural history, and parasites of mammals of Cook County, Minnesota. Bell Museum of Natural History Occasional Papers 14. University of Minnesota, Minneapolis. 56 pp.
Whitaker, J. O., Jr. 1999. Smoky Shrew (Sorex fumeus). Pages 22-23 in D. E. Wilson and S. Ruff, editors. The Smithsonian Book of North American Mammals. Smithsonian Institution Press in association with the American Society of Mammalogists, Washington.