Cryptotis parva (Say, 1823)
North American Least Shrew
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Basis for Listing
The least shrew is widely distributed across the eastern United States, and southward into Central America. However, it is only known in Minnesota from a single male specimen collected in Winona County in 1914. Small mammal surveys targeting this species in 1982 and 1996 failed to reconfirm the species' presence in the southeastern corner of the state. Records from Wisconsin, north-central Iowa, and South Dakota suggest that the least shrew could occur throughout southern Minnesota. Because of its apparent rarity in the state, the least shrew has been listed as a special concern species since 1984. Least shrews are small, inconspicuous, and do not leave obvious signs of their presence, so they can easily remain undetected. Least shrew remains found in owl pellets are often better indicators of their presence than are the results of trapping efforts.
The least shrew is one of the smallest shrews in North America. It has a short tail, tiny eyes, pointed nose, and inconspicuous ears. Its fur is dark brown to reddish brown on the back and gray on the underside. Typical adults are 68-86 mm (2.7-3.4 in.) in total length, with a tail length of 13-18 mm (0.5-0.7 in.). Weights range from 4-6.5 g (0.1 - 0.2 oz.). The least shrew can be distinguished from other shrews in Minnesota by its small size, short tail and dental characteristics.
Least shrews usually live in grassy or brushy areas, but they have also been found in forested habitats in the southern states. Farther north, they are most commonly found in open areas such as upland prairie, weedy fencerows and fields, meadows, and grassy or brushy roadsides. This shrew may also be found in moist microhabitats, but it is clearly not as dependent on mesic habitats as most northern shrews in the genus Sorex. In fact, although the ranges of the least shrew and the masked shrew (Sorex cinereus) broadly overlap, these two small shrews are rarely found together.
Biology / Life History
The broad range of habitats occupied by the least shrew may be related to the diversity of food items it consumes. These include most terrestrial insects and their larvae, earthworms, snails, carrion, and plant matter, as well as small mammals, frogs, and lizards. One least shrew may occupy a home range of about 0.2 ha (0.5 ac.). Evidence suggests that this shrew is highly social and may reach population densities greater than 5 per ha (2.5 ac.). Least shrews often cooperate in building nests that are shared during the nesting and wintering seasons. The nests are commonly shallow depressions or burrows under stones, logs, or stumps, and are made of dry grass, leaves, and shredded plant material. Females give birth in summer to 4-5 blind, naked young, which are cared for by both parents and weaned at approximately 21 days. The adults commonly raise 2-3 litters in a season. Least shrews construct runways in loose soil and under the snow and remain active all year. They have extremely high metabolic rates, and must eat nearly their own body weight every day.
Conservation / Management
Because least shrews utilize a broad range of habitats, protection of specific native plant communities or habitats will not ensure its presence in Minnesota. Reduction and degradation of suitable habitat, due to development and agricultural practices such as intensive farming and pesticide application, may be responsible for the apparent absence of the least shrew in the state. Efforts to define the range of least shrews in Minnesota should be continued, and where the species is found, local populations should be monitored and protected.
Conservation Efforts in Minnesota
The Minnesota Biological Survey targeted the least shrew during surveys in southeastern Minnesota in 1996, however, no new records were obtained. A survey of small mammal species reaching their distributional limits in southern and western Minnesota, conducted in 1982, also failed to document this species.
Birney, E. C. 1983. Status of small mammal species reaching distributional limits in southern and western Minnesota. Final report submitted to the Nongame Wildlife Program, Minnesota Department of Natural Resources. Unpaged.
Mumford, R. E., and J. O. Whittaker, Jr. 1982. Mammals of Indiana. Indiana University Press, Bloomington, Indiana. 537 pp.
Whitaker, J. O., Jr. 1974. Cryptotis parva. American Society of Mammalogists, Mammalian Species 43. 8 pp.