Sorex cinereus, commonly called the Masked shrew or common shrew, is the most widely distributed shrew found in North American. Common shrews occur throughout the northern United States, most of Canada, and Alaska. They do not occur on Vancouver Island, the Queen Charlotte Islands, in tundra habitats, arctic islands, or in extreme northern Quebec. (Nagorsen, 1996; van Zyll de Jong, 1983).
Common shrews occupy a diversity of habitats, most common are open and closed forests, meadows, river banks, lake shores, and willow thickets. Habitat suitability depends on the availability of water and the highest population densities can be found in moist environments. Common shrews also do well in disturbed habitats such as those disturbed by fire or logging. The average home range is 0.6 hectares (Nagorsen, 1996; Pagels, et al. 1994)).
Sorex cinereus is the second smallest shrew species. Sorex hoyi is slightly smaller. Although similar in size, their coloration is quite different. There is no significant sexual dimorphism in common shrews. Dorsal fur is brown, ventral fur is greyish-white. Pelage tends to be darker overall in winter. The tail is brown above and pale underneath, with a blackish tip. Average length of the tail is 39.9mm, comprising over 40% of the total length. Average length of adults is 99 mm. Young are born hairless and with fused eyelids, they weigh from 0.2 to 0.3 grams and are 15 to 17 mm long including a 3 mm long tail (Nagorsen, 1996; Wilson and Ruff, 1999; van Zyll de Jong, 1983).
Masked shrews probably do not live much past 1 to 2 years old, most probably die before reaching adulthood.
Common shrews are most active after dark, when 85 per cent of activity occurs. They are especially active between 01:00 and 02:00, when there has been a rainfall, or on very dark nights. Their primary activity is hunting. Common shrews hunt primarily on the ground but may also climb into low vegetation and shrubs. They run quickly, can jump to 10-15 cm high, and dig in loose substrate (Nagorsen, 1996; van Zyll de Jong, 1983).
Little is known of communication in masked shrews. They have an excellent sense of smell and can see fairly well. They use their sensitive whiskers to find their way around and detect prey. Masked shrews also probably squeak and hiss as a way of communicating.
Because Sorex cinereus inhabits a wide range there is great geographic variation in diet. Ants represent 50% of the food source for common shrews in Michigan, whereas insect larvae are the dominant prey item in New Brunswick. Kelp flies and marine amphipods are major dietary items in Nova Scotia. They are also important predators of forest insect pests such as Jack Pine Budworms and Larch Sawflies. In general, common shrews consume a variety of invertebrates including insect larvae, ants, beetles, crickets, grasshoppers, spiders, harvestmen, centipedes, slugs, snails. Seeds and fungi are also consumed (Nagorsen, 1996).
Masked shrews avoid being preyed upon by staying under cover and being active mostly at night, they are rarely seen.
Masked shrews can be very abundant in the communities in which they live. They can have a dramatic impact on insect communities because they have to consume such large quantities of insects. They are also important prey items for many small predators.
The extent to which common shrew populations affect humans is unknown. However, they have a significant impact on populations of insect pests and are important members of communities (Nagorsen, 1996).
Negative impacts of S. cinereus are unknown. However, they may affect populations of some beneficial organisms or inhibit reproduction of some plants by consuming seeds (Nagorsen, 1996).
Common shrews are common and widespread and none of the Genus Sorex, including Sorex cinereus, are considered to be threatened or endangered species (Boyd et al., 1999; Nagorsen, 1996; Wilson and Ruff, 1999).
Wendy Lee (author), University of Toronto.
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.
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.
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.
an animal that mainly eats meat
uses smells or other chemicals to communicate
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.
parental care is carried out by females
union of egg and spermatozoan
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
fertilization takes place within the female's body
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).
marshes are wetland areas often dominated by grasses and reeds.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.
breeding is confined to a particular season
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.
uses touch to communicate
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).
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
Boyd, S., K. Carlin-Morgan, B. Coslick, A. Edwards, M. Flood. June 1, 2000. "Mammals: Sorex cinereus, S. fumeus, S. longirostris & Microsorex hoyi" (On-line). Accessed October 6, 2000 at http://museum.nhm.uga.edu/~GA Wildlife/.
Nagorsen, D. 1996. Opossums, Shrews and Moles of British Columbia. UBC Press/Vancouver: Royal British Columbia Museum Handbook ISSN 118-5114.
Pagels, J., K. Uthus, H. Duval. 1994. The Masked Shrew, Sorex cinereus, in a Relictual Habitat of the Southern Applachian Mountains. Pp. 103-109 in J Merritt, G Kirkland, R Rose, eds. Advances in the Biology of Shrews. Pittsburgh, PA: Carnegie Museum of Natural History Special Publication No. 18.
Wilson, D., S. Ruff. 1999. The Smithsonian Book of North American Mammals. Washington and London: Smithsonian Institution Press.
van Zyll de Jong, C. 1983. Handbook of Canadian Mammals. vol. 1, Marsupials and Insectivores. Ottawa, Canada: National Museums of Canada.