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Sorex arcticusArctic shrew

By Stephanie Seto

Geographic Range

Arctic shrews, Sorex arcticus, are native to North America. Their distribution ranges as from the Arctic Circle in the north and as far south as the northern United States, into North and South Dakota, Wisconsin, Michigan, and Minnesota. Their eastern limits are in eastern Quebec and the Atlantic Maritime provinces, and their western limits are the southern Yukon and Mackenzie valleys. (Churchfield, 1990; Kirkland and Schmidt, 1996)

Habitat

Sorex arcticus occupies a variety of habitats, but populations are highest in moist grassy areas near lakes, bogs, swamps, and ditches. Specifically, in the Upper Peninsula of Michigan, arctic shrew populations are the densest in spruce and tamarack swamps, as well as near lakes and streams. They are often found in clearings in boreal forests, as well as marshes. Other occasional habitats include dry fields, old fields, mixed conifer swamps, dense grasses adjacent to ditches, mixed grasses, strawberries and ferns at forest clearings, alder thickets, and dry marsh with grasses, sedge hammocks, forbs, cattail, willow, and red-osier shrubs. (Baker, 1983; Kirkland and Schmidt, 1996; Kurta, 1998; Baker, 1983; Kirkland and Schmidt, 1996; Kurta, 1998)

Physical Description

Arctic shrews are medium-sized shrews with cylindrical bodies. The head is long with a pointed nose, like other shrews. The hair is short and soft, the eyes and ear pinnae are all very small, and the tail is long. (Baker, 1983; Kirkland and Schmidt, 1996)

The mass of S. arcticus ranges from 5.3 to 13.5 g. Total length ranges from 100 to 125 mm. Tail length ranges from 36 to 45 mm. The hind foot length ranges from 12 to 15 mm. (Clough, 1963)

The most distinctive physical characteristic of Sorex arcticus is its coloring. The fur is tri-colored, which is most evident during the winter months. On the dorsal side, from the head to the base of the tail, the fur is very dark brown to black in color. The sides are a lighter brown, and the ventral side of the body is a grayish brown. The tail is bi-colored; the dorsal side of the tail is dark brown and gradually becomes a light brown towards the ventral side. (Baker, 1983; Kirkland and Schmidt, 1996; Kurta, 1998)

Arctic shrews show slight seasonal variation in pelage. Tri-color bands are more distinct during the winter months, from October to June. Like others in the genus Sorex, arctic shrews molt twice a year. Winter fur is thicker and brighter. Summer fur is less insulative and paler. Also, the banded fur pattern is less developed in juveniles. (Baker, 1983; Clough, 1963)

The dental formula for Sorex is I 3/1, C 1/1, P 3/1, M 3/3, with thirty-two teeth total. Teeth have a brownish-red pigment on the tips. Sorex arcticus, like other Sorex, possesses unicuspid teeth after the canines. Arctic shrews have four unicuspids; the first two unicuspids are large and equal in size, and the third is smaller than the first two, but larger than the fourth. (Baker, 1983; Kirkland and Schmidt, 1996)

The metabolic rate of S. arcticus falls between the smaller masked shrew and the larger northern short-tailed shrew. The estimated minimal metabolic rate in S. arcticus is 4.7 kcal per day. (Buckner, 1964; Kirkland and Schmidt, 1996)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    5.3 to 13.5 g
    0.19 to 0.48 oz
  • Range length
    100 to 125 mm
    3.94 to 4.92 in

Reproduction

No information is available on the mating system of S. arcticus. However, most shrews mate promiscuously. During the breeding season, males compete for reproductive females and in doing so, move farther from their home ranges than females. It is likely that S. arcticus is similar. (Muller and Thalmann, 2000; Stockley and Searle, 1994)

In Wisconsin, the breeding season is from February to August. The breeding season is shorter in more northern areas, from April to August. Arctic shrew females give birth to 1 or 2 litters each year. Litter sizes range from 4 to 10 offspring, with an average of 7 offspring per litter. The gestation period ranges between 13 and 21 days. The lactation period ranges between 20 and 24 days. The time from conception to weaning lasts between 5 and 6.5 weeks. Both female and male arctic shrews reach sexual maturity after one year. (Baird, et al., 1983; Baker, 1983; Clough, 1963)

  • Breeding interval
    Arctic shrew females give birth to one or two litters each year.
  • Breeding season
    Breeding occurs from February to August, varying with latitude.
  • Range number of offspring
    4 to 10
  • Average number of offspring
    6.57
    AnAge
  • Range gestation period
    13 to 21 days
  • Range weaning age
    20 to 24 days
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    365 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    1 years

Newborn arctic shrews are helpless. They remain with and are cared for by their mother until the end of the weaning period. The young stay with their mother until 5 to 6.5 weeks after conception. Males play no role in parental care. (Kirkland and Schmidt, 1996)

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

Lifespan/Longevity

In the wild, individual arctic shrews can live as long as 18 months. The juvenile mortality rate is approximately 50% during the first month. (Buckner, 1966)

  • Average lifespan
    Status: wild
    18 months

Behavior

Sorex arcticus is a solitary species. In one laboratory study, whenever two arctic shrews were placed together in a cage, one was dead within several days. There was no sign of injury to the dead shrew, however. In another laboratory study, arctic shrews were placed in a cage with meadow voles. There was never physical contact between the two species, just alternating behaviors of approach and withdrawal from both animals. (Clough, 1963)

Arctic shrews are active during day and night. There are contradicting reports on levels and cycles of activity throughout the day. One claim is that they are least active between 0600 h and 1000 h, while another reports alternating periods of activity and rest, with an average of fourteen periods of activity daily. (Buckner, 1964; Clough, 1963; Kirkland and Schmidt, 1996)

Arctic shrews are very active and move quickly. Periods of inactivity are spent lying on the ground, either on one side or with the ventral side down, body rolled up, and head tucked under the body. Grooming consists ofwiping the forefeet rapidly along the mouth. (Clough, 1963)

Arctic shrews spend most of their time alone. Two arctic shrews cannot live together in a cage in laboratories, since one always dies. The cause of this is unclear, since the dead shrew has not been injured or bitten. (Clough, 1963)

  • Average territory size
    405 m^2

Home Range

The density of arctic shrews is usually 3 to 5 individuals per acre. Each individual usually limits its activity to 1/10 of an acre. (Baker, 1983; Kurta, 1998)

Communication and Perception

No information is available specifically for S. arcticus, but in general, olfaction is the strongest and most developed sense in shrews. A large portion of a shrew's brain is devoted to olfaction. (Baron, et al., 1983)

Shrews have limited visual ability. The eyes of shrews are very small, and the optic region of the shrew brain is small. (Hutterer, 1985; LeGros, 1932)

Shrews lack fully ossified auditory bullae, but they can produce and perceive sounds in high frequencies. Calls are made for defense and courtship, and calls are also made because of fright. (Branis and Burda, 1994; Hutterer, 1985)

Touch is probably important to shrews. Mothers touch their young, and mates touch each other.

Food Habits

Arctic shrews are insectivorous. Larch sawflies make up a large proportion of the diet. Arctic shrews also eat grasshoppers such as redlegged grasshoppers. Generally, they feed on insect larvae, pupae, and adults, and occasionally other invertebrates. Aquatic insects are also consumed, since arctic shrews sometimes reside near streams and bog banks. In captivity, arctic shrews consume dead voles, fly pupae, and mealworms. (Buckner, 1970; Kurta, 1998)

Sorex arcticus usually forages on the ground, but will also climb plants. Arctic shrews exhibit hunting behavior, preying on grasshoppers. Sorex arcticus has been observed to attack adult Melanoplus ferumrubrum grasshoppers by climbing approximately 31 cm and pouncing on the prey, seizing it with jaws and feet. (Baker, 1983; Jackson, 1961; Kirkland and Schmidt, 1996; Baker, 1983; Buckner, 1970; Jackson, 1961; Kirkland and Schmidt, 1996)

  • Animal Foods
  • mammals
  • carrion
  • insects
  • terrestrial non-insect arthropods
  • terrestrial worms

Predation

A defense strategy of arctic shrews is excreting a musky scent from its flank glands, a strategy also used in other shrew species. Arctic shrews also remain under cover most of the time and are colored in a waywhich helps to hide them. (Baker, 1983)

The only known predators of arctic shrews are owls. The remains of an arctic shrew have been found in a great horned owl pellet. (Kurta, 1998; Nelson, 1934)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Arctic shrews may have a role in regulating insect pest populations.

In regions where Sorex arcticus and S. cinereus distributions overlap, population sizes are found to be inversely related to each other, suggesting direct competition. (Buckner, 1966)

Sorex arcticus associates with many other small mammals. The most common and frequent ecological associations occur with masked shrews, meadow voles, and northern short-tailed shrews. Other small mammal species that share habitats with arctic shrews are water shrews, pygmy shrews, deer mice, southern red-backed voles, heather voles, southern bog lemmings, meadow jumping mice, ermines, eastern chipmunks, least chipmunks, and red squirrels. (Kirkland and Schmidt, 1996)

Arctic shrews are susceptible to various ectoparasites. These include hypopial mites (Labidophorus soricis), larval ticks (Ixodes muris), myobiid mites (Proomyobia breviseosus and Amorphacarus elongatus), laelapid mites (Androlaelops fahrenholzi), ixodid ticks (Haemaphysalis leporispalustris and Ixodes murinus), Parasitoidea ticks (Euhaemogamasus liponyssoides and Monyssus jamesoni), trombiculid mites (Trombicula harperi) and other Trombicula, myobid mites (Amorphacarus henegerorum), pyemotid mites in the genus Resinacaris, and fleas (Corrodopsylla curvata). (Lawrence, et al., 1965; Whitaker and Pascal, 1971)

Commensal/Parasitic Species
  • hypopial mites (Labidophorus soricis)
  • larval ticks (Ixodes muris)
  • myobiid mite (Proomyobia breviseosus)
  • myobiid mite (Amorphacarus elongatus)
  • laelapid mites (Androlaelops fahrenholzi)
  • ixodid tick (Haemaphysalis leporispalustris)
  • ixodid tick (Ixodes murinus)
  • Parasitoidea tick (Euhaemogamasus liponyssoides)
  • Parasitoidea tick (Monyssus jamesoni)
  • trombiculid mites (Trombicula harperi)
  • myobid mites (Amorphacarus henegerorum)
  • pyemotid mites (Resinacaris)
  • fleas (Corrodopsylla curvata)

Economic Importance for Humans: Positive

There are no known positive effects of Sorex arcticus on humans.

Economic Importance for Humans: Negative

There are no known adverse affects of Sorex arcticus on humans.

Conservation Status

Arctic shrews are abundant in suitable habitats throughout their range.

Other Comments

Sorex arcticus is usually referred to as arctic shrews; however other common names are saddle-backed shrews, black-backed shrews, and musaraigne arctique. ("Sorex arcticus", 2006)

There are three subspecies of Sorex arcticus: S. a. arcticus, S. a. laricorum, and S. a. maritimensis. (Kirkland and Schmidt, 1996)

During the Pleistocene, arctic shrews occurred farther south than they do today. The present range of arctic shrew populations was covered by ice during the Pleistocene. Most arctic shrew fossil records are from Pleistocene deposits from the central and southern Appalachian Mountains, and from the Great Plains. Earliest records are from Colorado and Virginia, from the Late Irvingtonian, between 690,000 to 900,000 years before present. (Kirkland and Schmidt, 1996)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Nancy Shefferly (editor), Animal Diversity Web.

Stephanie Seto (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor.

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

carrion

flesh of dead animals.

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

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

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).

marsh

marshes are wetland areas often dominated by grasses and reeds.

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

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

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

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

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

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

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

2006. "Sorex arcticus" (On-line). Integrated Taxonomic Information System. Accessed March 18, 2006 at http://www.itis.usda.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=179935.

Baird, D., R. Timm, G. Nordquist. 1983. Reproduction in the arctic shrew, Sorex arcticus . Journal of Mammalogy, 64: 298-301.

Baker, R. 1983. Michigan Mammals. Detroit: Michigan State University Press.

Baron, G., H. Frahm, K. Bhatnagar, H. Stephan. 1983. Comparison of brain structure volumes in Insectivora and Primates III Main olfactory bulb (MOB). J. Hirnforsch, 24: 551-568.

Branis, M., H. Burda. 1994. Visual and hearing biology of shrews. Pp. 189-200 in J Merritt, G Kirkland, R Rose, eds. Advances in the Biology of Shrews, Special Publication no. 18. Pittsburgh: Carnegie Museum of Natural History.

Buckner, C. 1970. Direct observation of shrew predation on insects and fish. The Blue Jay, 28: 171-172.

Buckner, C. 1964. Metabolism, food capacity, and feeding behavior in four species of shrews. Canadian Journal of Zoology, 42: 259-279.

Buckner, C. 1966. Populations and ecological relationships of shrews in tamarack bogs of southwestern Manitoba. Journal of Mammalogy, 47: 181-194.

Churchfield, S. 1990. The Natural History of Shrews. Ithaca, NY: Cornell University Press.

Clough, G. 1963. Biology of the Arctic Shrew, Sorex arcticus. American Midland Naturalist, 69: 69-81.

Hutterer, R. 1985. Anatomical adaptations of shrews. Mammal Review, 15: 43-55.

Jackson, H. 1961. Mammals of Wisconsin. Madison: Wisconsin Press.

Kirkland, G., D. Schmidt. 1996. Sorex arcticus. Mammalian Species, 524: 1-5.

Kurta, A. 1998. Mammals of the Great Lakes Region. Ann Arbor: The University of Michigan Press.

Lawrence, W., K. Hays, S. Graham. 1965. Arthropodous ectoparasites from some northern Michigan mammals. Occasional Papers of the Museum of Zoology, University of Michigan, 639: 1-7.

LeGros, C. 1932. The brain of Insectivora. Proceedings of the Zoological Society of London: 975-1013.

Muller, A., U. Thalmann. 2000. Origin and evolution of primate social organization: a reconstruction.. Biological Review, 75: 405-435.

Nelson, A. 1934. Notes on Wisconsin mammals. Journal of Mammalogy, 15: 252-253.

Smithsonian Institution, 1993. "Sorex arcticus" (On-line). MSW Scientific Names. Accessed March 18, 2006 at http://nmnhgoph.si.edu/cgi-bin/wdb/msw/names/query.

Stockley, P., J. Searle. 1994. Characteristics of the breeding season in the common shrew (Sorex araneus): male sexual maturation, morphology and mobility. Pp. 181-188 in J Merritt, G Kirkland, R Rose, eds. Advances in the Biology of Shrews, Special Publication no. 18. Pittsburgh: Carnegie Museum of Natural History.

Whitaker, J., D. Pascal. 1971. External parasites of the arctic shrew in Minnesota.. Journal of Mammalogy, 52: 202.

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