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) Biogeographic Regions

nearctic native



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) 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. (Baird, et al., 1983; Baker, 1983; Clough, 1963) Key Reproductive Features

iteroparous

seasonal breeding

gonochoric/gonochoristic/dioecious (sexes separate)

sexual

fertilization

viviparous 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) Key Behaviors

terricolous

diurnal

nocturnal

crepuscular

motile

sedentary

solitary

territorial 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)

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 Known Predators great horned owls (Bubo virginianus)



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.

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. 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 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.