Sorex tundrensis
tundra shrew

Sorex tundrensis is a Nearctic species. It ranges through most of Alaska, including Kodiak Island and across the Bering Strait into northeastern Siberia, where it is proposed that the closest relatives of S. tundrensis are found (van Zyll de Jong 1983). In Canada, its range includes northern Yukon Territory, the Mackenzie Delta region of the Northwest Territories, and the extreme northwestern part of British Columbia (van Zyll de Jong 1983). Sorex tundrensis has a limited distribution in British Columbia, being confined to the Haines Triangle region (Nagorsen 1996). (Nagorsen, 1996; van Zyll de Jong, 1983)

Sorex tundrensis inhabits a variety of alpine and arctic habitats as well as forests, shrublands, and meadows. Habitats include a variety of dwarf trees and shrubs, including Betula, Salix, and Ledum species (van Zyll de Jong 1983). They are found in mossy bog habitats but seem to prefer habitats that are more dry than do sympatric species of shrews, such as barren ground shrews, Sorex ugyanak (MacDonald 2003). (MacDonald, 2003; van Zyll de Jong, 1983)

Tundra shrews are medium-sized, stocky shrews. In Canada mass ranges from 4.9 to 10.0 g (average 6.8 g). Head and body length is between 84 and 115 mm (average 97 mm) and tail length ranges from 25 to 37 mm (average 31 mm). In Alaska, the mass ranges from 3.8 to 10.0 g (average 6.6 g). Head and body length is between 83 to 120 mm (average 95 mm) and tail length ranges from 20 to 36 mm (average 29 mm). (MacDonald, 2003; Nagorsen, 1996)

Sorex tundrensis has a distinct pelage that varies seasonally and with age. In summer adults have a tricolor pelage, with a dark brown back, pale brown sides, and a pale gray belly (Keys and Wilson 2002). The difference between back and belly pelage is less distinct in juveniles and subadults. In winter pelage is bicolored, consisting of a brown back and grayish sides and belly. Pelage is also longer in winter than in summer (van Zyll de Jong 1983). The tail is bicolored, with the top notably more brownish than the bottom and darker towards the tip. The winter molt begins in April and May and continues into June. In August and September, the winter fur begins to grow and the fall molt is completed in November (van Zyll de Jong 1999). (Kays and Wilson, 2002; van Zyll de Jong, 1983; van Zyll de Jong, 1999)

Sorex tundrensis and its close relative, S. arcticus, are similarly patterned, but the latter has a longer tail with a much darker back. Sorex tundrensis is larger than S. ugyunak, as well as having a shorter tail. (Kays and Wilson, 2002; MacDonald, 2003)

The dental formula is 3/1, 1/1, 3/1, 3/3 = 32 teeth. (Forsyth, 1999)

Longevity ranges from 12 to 18 months and maturity is probably the spring following birth (Forsyth 1999). Nothing is known about the longevity of S. tundrensis in captivity. However, in other soricids, life expectancy varies from season to season, and susceptibility to death is believed to be highest during the juvenile stage and the breeding period (Churchfield 1990). (Churchfield, 1990; Forsyth, 1999)

Information on the behavior of S. tundrensis is limited. Other soricids appear to be active at all hours of the day in the summer and winter and are solitary. The activity of S. tundrensis is not known in winter (van Zyll de Jong 1983). Because fat storage in shrews is minimal, hibernation is not feasible (Churchfield 1990). (Churchfield, 1990; van Zyll de Jong, 1983)

Home Range

The home range of S. tundrensis and its movements have not yet been investigated. Other Sorex species maintain non overlapping home ranges in which they nest and forage. During the breeding season home ranges of males may overlap those of several females. Home range sizes vary with season, sex, and food availability. (Churchfield, 1990)

Little is known about the communication in S. tundrensis. However, other Sorex species use well-developed olfactory, tactile, and auditory senses. Shrews use their long snouts, covered with vibrissae, for locating prey. The tip of the snout is a highly sensitive glandular pad or rhinarium. Olfaction is also used socially in shrews. There are many scent glands that are scattered in the skin that cover most of the body. These scent glands are probably used in communicating sexual state and marking territories. (Churchfield, 1990)

Shrew species communicate with different types of calls as well, for example, chirps are sometimes used in courtship. (Churchfield, 1990)

Little is known about the food habits of S. tundrensis. In Alaska they were found to eat insects, larvae, earthworms, and floral parts of small grasses (van Zyll de Jong 1983). Tundra shrews, like other shrews, must forage almost continually to fuel their high metabolic rates. (Churchfield, 1990; van Zyll de Jong, 1983)

Tundra shrews are preyed on by owls, hawks, snakes, and small mammalian carnivores, such as weasels. It is suggested that their foul odor deters some predators, such as domestic cats. (Churchfield, 1990; Forsyth, 1999)

Little is known about the ecosystem roles of S. tundrensis. Other shrews in the genus Sorex are very important in regulating invertebrate prey populations. (Platt and Blakley, 1973)

There are no known adverse affects of S. tundrensis on humans. Other shrews have been known to prey on Douglas fir seeds, which could have an effect on the regeneration of Douglas firs. (Churchfield, 1990)

Shrews are voracious predators of insect larvae and play an important part in regulating pest species. (Churchfield, 1990)

Sorex tundrensis is of least concern on the IUCN list. It is not listed on CITES appendices or the United States Endangered Species Act.

Tundra shrews, Sorex tundrensis, were once considered to be a subspecies of S. arcticus (MacDonald 2003). More recent literature, however, has treated S. tundrensis as a distinct Nearctic species. When specimens of S. arcticus from Edmonton, Alberta were compared with specimens of S. tundrensis from the Northwest Territories they were found to differ substantially in all external measurements except for except for hind foot length and nearly all cranial measurements. In addition to differences in size, the two species also differ in the morphology of their auditory ossicles (Youngman 1975). Moreover, George (1988) found that S. tundrensis was a genetically distinct species from S. arcticus based on a molecular study of 26 allozyme loci. Sorex tundrensis is a Beringian species, unlike S. arcticus, suggesting that the ancestor of tundra shrews entered North America from Asia when Alaska and Siberia were still connected at the Bering Strait (van Zyll de Jong 1983). (George, 1988; MacDonald, 2003; van Zyll de Jong, 1983; Youngman, 1975)

Sorex tundrensis is a member of the Sorex araneus group, which has trivalent sex chromosomes (X, Y1, and Y2) in males (Lukacova, et al. 1996). Other species belonging to this group are European common shrews (Sorex araneus) and Arctic shrews (Sorex arcticus) (van Zyll de Jong 1983). Interestingly, Palearctic populations of S. tundrensis have a karyotype that is considered most primitive in Sorex araneus group (Lukacova et al. 1996). For this reason, Volobouev (1989) has suggested that tundra shrews are the oldest lineage of extant species in the araneus group. (Lukacova, Zima, and Volobouev, 1996; van Zyll de Jong, 1983; Volobouev, 1989)