Sorex arcticus is usually referred to as arctic shrews; however other common names are saddle-backed shrews, black-backed shrews, and musaraigne arctique.
There are three subspecies of Sorex arcticus: S. a. arcticus, S. a. laricorum, and S. a. maritimensis.
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.
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.
Shrews have limited visual ability. The eyes of shrews are very small, and the optic region of the shrew brain is small.
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.
Touch is probably important to shrews. Mothers touch their young, and mates touch each other.
Communication Channels: visual ; tactile ; acoustic ; chemical
Other Communication Modes: pheromones ; scent marks
Perception Channels: visual ; tactile ; acoustic ; chemical
Arctic shrews are abundant in suitable habitats throughout their range.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: least concern
There are no known adverse affects of Sorex arcticus on humans.
There are no known positive effects of Sorex arcticus on humans.
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.
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.
Arctic shrews are susceptible to various ectoparasites. These include hypopial mites (Labidophorus soricis), larval ticks (Ixodes scapularis), 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).
Commensal/Parasitic Species:
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.
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.
Animal Foods: mammals; carrion ; insects; terrestrial non-insect arthropods; terrestrial worms
Primary Diet: carnivore (Insectivore )
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.
Biogeographic Regions: nearctic (Native )
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.
Habitat Regions: temperate ; terrestrial
Terrestrial Biomes: taiga ; savanna or grassland ; forest
Wetlands: marsh ; swamp ; bog
Other Habitat Features: riparian
In the wild, individual arctic shrews can live as long as 18 months. The juvenile mortality rate is approximately 50% during the first month.
Average lifespan
Status: wild: 18 months.
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.
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.
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.
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.
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.
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.
Range mass: 5.3 to 13.5 g.
Range length: 100 to 125 mm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: sexes alike
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.
The only known predators of arctic shrews are owls. The remains of an arctic shrew have been found in a great horned owl pellet.
Known Predators:
Anti-predator Adaptations: cryptic
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.
Mating System: polygynandrous (promiscuous)
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.
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.
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 (male): 1 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; viviparous
Average number of offspring: 6.57.
Average age at sexual or reproductive maturity (female)
Sex: female: 365 days.
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.
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)
The Arctic shrew (Sorex arcticus), also known as the blackback shrew or saddlebacked shrew, is a medium-sized shrew found in Canada and the northern United States. Separate species status has been proposed for the maritime shrew (Sorex maritimensis) which is found in New Brunswick and Nova Scotia and had been considered to be a subspecies of the Arctic shrew. The tundra shrew (Sorex tundrensis) was formerly considered to be a subspecies of the Arctic shrew.
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 an average metabolism of 4.7 kilocalories a day.
Arctic shrews are native to North America, ranging 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.
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 lakes, streams, marshes, wetlands, bogs, swamps, ditches or open areas near wetlands. In the Upper Peninsula of Michigan, they are found densely in spruce and tamarack 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, and red-osier shrubs.
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, 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 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.
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.[3] 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.[4]
Like all shrews, the Arctic shrew has a voracious and insatiable appetite due to its quick metabolism. It eats insects, worms and small invertebrates, 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.[4]
There are two subspecies recognized for this species:[1]
The Arctic shrew (Sorex arcticus), also known as the blackback shrew or saddlebacked shrew, is a medium-sized shrew found in Canada and the northern United States. Separate species status has been proposed for the maritime shrew (Sorex maritimensis) which is found in New Brunswick and Nova Scotia and had been considered to be a subspecies of the Arctic shrew. The tundra shrew (Sorex tundrensis) was formerly considered to be a subspecies of the Arctic shrew.
