The Arctic Shrew also known as the Blackback Shrew or Saddlebacked Shrew, is a medium-sized shrew

Shrew

A shrew or shrew mouse is a small molelike mammal classified in the order Soricomorpha. True shrews are also not to be confused with West Indies shrews, treeshrews, otter shrews, or elephant shrews, which belong to different families or orders.Although its external appearance is generally that of...

 found in Canada

Canada

Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

 and the northern United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. Separate species status has been proposed for the Maritime Shrew

Maritime Shrew

The Maritime Shrew is a species of mammal in the family Soricidae. It is found in New Brunswick and Nova Scotia in Canada....

 (Sorex maritimensis) which is found in New Brunswick

New Brunswick

New Brunswick is one of Canada's three Maritime provinces and is the only province in the federation that is constitutionally bilingual . The provincial capital is Fredericton and Saint John is the most populous city. Greater Moncton is the largest Census Metropolitan Area...

 and Nova Scotia

Nova Scotia

Nova Scotia is one of Canada's three Maritime provinces and is the most populous province in Atlantic Canada. The name of the province is Latin for "New Scotland," but "Nova Scotia" is the recognized, English-language name of the province. The provincial capital is Halifax. Nova Scotia is the...

 and had been considered to be a subspecies of the Arctic Shrew. The Tundra Shrew

Tundra Shrew

The Tundra Shrew is a small shrew found in Alaska, the northern Yukon Territory, the MacKenzie Delta region of the Northwest Territories, extreme northwestern British Columbia and eastern Russia...

 (Sorex tundrensis) was formerly considered to be a subspecies of the Arctic Shrew.

Physical description

The Arctic Shrew is most distinctive in its tricolored fur. It is dark brown or black on its back from its head to the base of its tail, while its flanks are a lighter brown, and its underside is lighter still grayish brown. Even its tail is bi-colored, dark brown on the dorsal side, and gradually fading to a lighter brown on the ventral side. The fur is grayer in winter time, and its tricolor is most marked during the winter months from October to June, for the fur is thicker and brighter. Arctic shrews molt twice a year, and the tricolor bands in the fur are less prominent in younger shrews.

Its body length ranges from 10 cm to 12 cm including a 4 cm long tail. Its mass may range from 5 g to 13 g and it possesses thirty-two teeth with and average metabolism of 4.7 kilocalories a day.

Distribution and habitat

Arctic shrews are native to North America, ranging from the Arctic Circle

Arctic Circle

The Arctic Circle is one of the five major circles of latitude that mark maps of the Earth. For Epoch 2011, it is the parallel of latitude that runs north of the Equator....

 in the north and as far south as the northern United States

Northern United States

Northern United States, also sometimes the North, may refer to:* A particular grouping of states or regions of the United States of America. The United States Census Bureau divides some of the northernmost United States into the Midwest Region and the Northeast Region...

, into North

North Dakota

North Dakota is a state located in the Midwestern region of the United States of America, along the Canadian border. The state is bordered by Canada to the north, Minnesota to the east, South Dakota to the south and Montana to the west. North Dakota is the 19th-largest state by area in the U.S....

 and South Dakota

South Dakota

South Dakota is a state located in the Midwestern region of the United States. It is named after the Lakota and Dakota Sioux American Indian tribes. Once a part of Dakota Territory, South Dakota became a state on November 2, 1889. The state has an area of and an estimated population of just over...

, Wisconsin

Wisconsin

Wisconsin is a U.S. state located in the north-central United States and is part of the Midwest. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake Michigan to the east, Michigan to the northeast, and Lake Superior to the north. Wisconsin's capital is...

, Michigan

Michigan

Michigan is a U.S. state located in the Great Lakes Region of the United States of America. The name Michigan is the French form of the Ojibwa word mishigamaa, meaning "large water" or "large lake"....

, and Minnesota

Minnesota

Minnesota is a U.S. state located in the Midwestern United States. The twelfth largest state of the U.S., it is the twenty-first most populous, with 5.3 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the thirty-second state...

. Their eastern limits are in eastern Quebec

Quebec

Quebec or is a province in east-central Canada. It is the only Canadian province with a predominantly French-speaking population and the only one whose sole official language is French at the provincial level....

 and the Atlantic Maritime provinces, and their western limits are the southern Yukon

Yukon

Yukon is the westernmost and smallest of Canada's three federal territories. It was named after the Yukon River. The word Yukon means "Great River" in Gwich’in....

 and Mackenzie valleys.

Arctic shrews are found in a variety of habitats in highest density of 3 to 5 individuals per acre and each individual arctic shrew appears to limit its range to one tenth of an acre. Of their various habitats, they found in greatest quantity and density in areas near bodies of water, such as lake

Lake

A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...

s, streams, marsh

Marsh

In geography, a marsh, or morass, is a type of wetland that is subject to frequent or continuous flood. Typically the water is shallow and features grasses, rushes, reeds, typhas, sedges, other herbaceous plants, and moss....

es, wetland

Wetland

A wetland is an area of land whose soil is saturated with water either permanently or seasonally. Wetlands are categorised by their characteristic vegetation, which is adapted to these unique soil conditions....

s, bog

Bog

A bog, quagmire or mire is a wetland that accumulates acidic peat, a deposit of dead plant material—often mosses or, in Arctic climates, lichens....

s, swamp

Swamp

A swamp is a wetland with some flooding of large areas of land by shallow bodies of water. A swamp generally has a large number of hammocks, or dry-land protrusions, covered by aquatic vegetation, or vegetation that tolerates periodical inundation. The two main types of swamp are "true" or swamp...

s, ditches or open areas near wetlands. In the Upper Peninsula of Michigan, they are found densely in spruce

Spruce

A spruce is a tree of the genus Picea , a genus of about 35 species of coniferous evergreen trees in the Family Pinaceae, found in the northern temperate and boreal regions of the earth. Spruces are large trees, from tall when mature, and can be distinguished by their whorled branches and conical...

 and tamarack

Tamarack Larch

Tamarack Larch, or Tamarack, or Hackmatack, or American Larch is a species of larch native to Canada, from eastern Yukon and Inuvik, Northwest Territories east to Newfoundland, and also south into the northeastern United States from Minnesota to Cranesville Swamp, West Virginia; there is also a...

 swamps, in addition to other typical habitats. Arctic shrews have been found in clearings in boreal forests, and occasionally in mixed conifer swamps, dry or old fields, dense grasses near ditches, mixed grasses, in the undergrowth of forest clearings, alder thickets, and dry marsh with grasses, sedge hammocks, forbs, cattail, willow

Willow

Willows, sallows, and osiers form the genus Salix, around 400 species of deciduous trees and shrubs, found primarily on moist soils in cold and temperate regions of the Northern Hemisphere...

, and red-osier shrubs.

Mating and reproduction

There is little information about the mating habits of the Arctic Shrew, however males of most shrew species mate with many females, and compete with other males for females, so the assumption is that arctic shrews behave similarly. In Wisconsin

Wisconsin

Wisconsin is a U.S. state located in the north-central United States and is part of the Midwest. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake Michigan to the east, Michigan to the northeast, and Lake Superior to the north. Wisconsin's capital is...

, the breeding season lasts from February to August, and the breeding season is shorter in more northern areas, from April to August. Arctic shrew females give birth to one or two litters each year, and these litters range in size from 4 to 10 offspring, with an average of 7 offspring per litter. The gestation period ranges between 13 and 21 days, so the young stay with their mother until 5 to 6.5 weeks after conception, and males make no contribution to parental care. When they are born, young arctic shrews are helpless. Their mother and are cares for them until the end of the weaning period, 20 to 24 days after birth. Both female and male arctic shrews reach sexual maturity after one year. As much as 50 percent of all juveniles die in the first month, but the average lifespan of an arctic shrew in the wild is around 18 months.

Behavior

Arctic shrews are solitary animals. Adults are territorial. In one laboratory study, whenever two arctic shrews were placed together in a cage, one was dead within several days, though there was no sign of injury to the dead shrew and the cause for this mortality is unclear, however the result of this forced interaction has been repeatedly observed. Arctic shrews are active during day and night, though there are contradicting reports on levels and cycles of activity throughout the day. One claim is that they are least active during mid-morning, while other reports describe alternating periods of activity and rest, with an average of fourteen periods of activity daily. 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 of wiping the forefeet rapidly along the mouth.

Like all shrews, the Arctic Shrew has a voracious and insatiable appetite due to its quick metabolism. It eats insects, worms and small invertebrate

Invertebrate

An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...

s, with a large proportion of its diet made up of larch sawflies, though arctic shrews in captivity have been fed dead voles fly pupae, and mealworms. The only known predators of arctic shrews are owls

Great Horned Owl

The Great Horned Owl, , also known as the Tiger Owl, is a large owl native to the Americas. It is an adaptable bird with a vast range and is the most widely distributed true owl in the Americas.-Description:...

.

Subspecies

There are three subspecies recognized for this species:

• Sorex arcticus arcticus
• Sorex arcticus laricorum