Sorex tundrensistundra shrew

Geographic Range

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; Nagorsen, 1996; van Zyll de Jong, 1983)

Habitat

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)

Physical Description

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)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    3.8 to 10 g
    0.13 to 0.35 oz
  • Range length
    83 to 120 mm
    3.27 to 4.72 in

Reproduction

Males become sexually active in the summer, but reproductive activity decreases as autumn approaches (van Zyll de Jong 1983). Churchfield (1990) found that the flank glands in soricids are prominent in adult males and may act in attracting females for breeding. There is little specific information on reproduction in S. tundrensis. (Churchfield, 1990; van Zyll de Jong, 1983)

There is not a lot of information on the breeding biology of this species. However, pregnant females have been recorded in June, July, and September. Numbers of embryos range from 8 to 12, with an average of 10 (van Zyll de Jong 1983). Females probably produce several litters in a season and are capable of breeding in their first summer (Nagorsen 1996). Gestation is poorly understood, but has been suggested to range from 13 to 28 days, with number of offspring ranging from 8 to 12 (Forsyth 1999). Tundra shrews breed in the spring following their birth. (Churchfield, 1990; Forsyth, 1999; van Zyll de Jong, 1983)

  • Breeding interval
    Tundra shrews breed several times during the breeding season.
  • Breeding season
    Tundra shrews breed during the warm season each year.
  • Range number of offspring
    8 to 12
  • Range gestation period
    13 to 28 days

Females nurse and protect their young in a nest until they become independent.

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

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)

  • Typical lifespan
    Status: wild
    12 to 18 months

Behavior

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)

Communication and Perception

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)

Food Habits

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)

  • Animal Foods
  • insects
  • terrestrial worms
  • Plant Foods
  • flowers

Predation

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)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

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)

Economic Importance for Humans: Positive

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

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

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)

Conservation Status

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

Other Comments

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, et al., 1996; van Zyll de Jong, 1983; Volobouev, 1989)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Cherish Yuke (author), University of Alaska Fairbanks, Link Olson (editor, instructor), University of Alaska Fairbanks.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

bog

a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

crepuscular

active at dawn and dusk

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

fertilization

union of egg and spermatozoan

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

taiga

Coniferous or boreal forest, located in a band across northern North America, Europe, and Asia. This terrestrial biome also occurs at high elevations. Long, cold winters and short, wet summers. Few species of trees are present; these are primarily conifers that grow in dense stands with little undergrowth. Some deciduous trees also may be present.

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tundra

A terrestrial biome with low, shrubby or mat-like vegetation found at extremely high latitudes or elevations, near the limit of plant growth. Soils usually subject to permafrost. Plant diversity is typically low and the growing season is short.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

Churchfield, S. 1990. The Natural History of Shrews. Ithaca, New York: Comstock Publishing Associates.

Forsyth, A. 1999. Mammals of North America: Temperate and Arctic Regions. Buffalo, New York: Firefly Books Ltd..

George, S. 1988. Systematics, historical biogeography, and evolution of the genus Sorex . Journal of Mammalogy, 69: 443-461.

Kays, R., D. Wilson. 2002. The Mammals of North America. Princeton, New Jersey: Princeton University Press.

Lukacova, L., J. Zima, V. Volobouev. 1996. Karyotypic variation in Sorex tundrensis (Soricidae, Insectivora). Heraditas, 125: 233-238.

MacDonald, S. 2003. The Small Mammals of Alaska: A Field Handbook of the Shrews and Small Rodents. Unpublished: Unpublished draft.

Nagorsen, D. 1996. Royal British Columbia Museum Handbook: Opossums, Shrews, and Moles of British Columbia Vol. 2. Victoria: UBC Press.

Platt, W., N. Blakley. 1973. Short-term effects of shrew predation upon invertebrate prey. Proceedings of the Iowa Academy of Science, 80: 60-66.

Volobouev, V. 1989. Phylogenetic relationships of the Sorex arneus-arcticus species complex (Insectivora, Soricidae) based on high-resolution chromosome analysis. Journal of Heredity, 80: 284-290.

Youngman, P. 1975. Mammals of the Yukon Territory. Ottawa, Canada: Publications in Zoology, No. 10. National Museums of Canada.

van Zyll de Jong, C. 1983. Handbook of Canadian Mammals. Part 1. Marsupials and Insectivores. Ottawa, Canada: National Museums of Natural Sciences.

van Zyll de Jong, C. 1999. Tundra Shrew. Pp. 44-45 in D Wilson, S Ruff, eds. The Smithsonian Book of North American Mammals. Washington D.C.: Smithsonian Institution Press.