Sorex cinereus
cinereus shrew
(Also: masked shrew)

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.

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).

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).

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).