The Cinereus Shrew or Masked Shrew (Sorex cinereus) is a small 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 Alaska

Alaska

Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...

, 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...

. This is the most widely distributed shrew in North America where it is also known as the Common Shrew.

Description

It is grey-brown in colour with a light grey underside and a pointed snout. It has a long tail which is brown on top and pale underneath with a dark tip. Its body is about 9 cm in length including a 4 cm long tail. It weighs about 5 g. It has darker coloring than other shrews. Masked shrews can live up to two years, but averagely only survive eighteen months.

Yom-Tov et al. (2005) found that the masked shrew body size opposes Bergmann’s rule, decreasing with latitude and increasing with January temperatures in Alaska. Also, Yom-Tov et al. (2005) showed that body and tail length increased with rising temperatures during the second half of the twentieth century. This may be due to higher temperatures increasing the availability of the shrews’ diets.

Distribution

The masked shrew is the most widely distributed shrew (Merritt 1995). Its range covers most of northern North America extending south as far down to Maryland, along the Rocky Mountains in the west, and to the Appalachians in the east. This species was introduced into Newfoundland in the late 1950s. It can be found in many types of habitat like arid grasslands, moist areas, woodland and tundra. The masked shrew mostly lives in humid areas and with high levels of vegetation to hide in. Moisture determines the abundance of this shrew.

Predation and Parasitism

Predators include larger shrews, hawks, owls, shrikes, snakes, herons, and foxes, leopard frog, bluebird, brown trout, and weasels.
Masked shrews are susceptible to many types of parasites, like fleas and tapeworms (Cowan 2007). Cowan et al. (2007) found that the high volume of food masked shrews consume causes them to be more susceptible to parasitism. Since males have larger ranges they have a higher exposure to parasites (Cowan 2007).

Diet and Prey

Masked shrews are opportunistic generalists. It eats insects, worms, snails, small mammals, salamanders, seeds and carrion. Due to its high metabolism, the masked shrew can eat three times its weight a day (Whitaker 2004). The shrews have to eat almost constantly because can only survive a few hours without food (Whitaker 2004). Their metabolism drops when they are at rest.

McCay et al. (1997) found a higher abundance of masked shrews in non-irrigated forests due to a higher availability of larval insects, which was the preferred food source of the masked shrew. Masked shrews chose Lepidoptera larva over other food sources (McCay 1997).

Behavior

This animal is active day and night year-round. Masked shrews can be nocturnal or diurnal depending on the weather. Doucet et al. (1974) showed that rain increases the nocturnal activity of the masked shrew, while cloud cover increases day and night activity. It digs tunnels but also uses tunnels created by other small mammals. It uses dry grass to make nests in these tunnels. It can make high frequency pulses and has lateral scent glands. The home range of the masked shrew depends on availability of food, but is averagely 0.55 hectare. It has a low tolerance for other shrews in its home range. Merritt et al. (1995) found that its mass declined by half from summer to winter and that non-shivering heat production, energy conservation, and reduced body mass In winter allows it survive winter

Reproduction

Masked shrews living at high latitudes are born in late spring and summer, reach adult size by the time they leave their nests and complete their life cycle within a year (Yom-Tov 2005). They are born during spring or summer, remain immature in winter, and breed the following spring (Merritt 1995). Masked shrews breed from May to September. Females have one litter of 6-7 young during the breeding season. The young are born hairless, clawless, and have translucent abdominal walls (Whitaker 2004). Body mass increases and peaks at twenty days, then decreases when the young leave the nest after about 27 days. Masked shrews have a high chance of mortality during their first two months of life and most die during the first year. Masked shrews become sexually mature at two months, but wait until their first spring to breed.

External Links

http://www.draperwildlife.org/MammalIndexpage/MaskedShrew.html
http://animaldiversity.ummz.umich.edu/site/resources/phil_myers/classic/shrew3.jpg/view.html
http://www.youtube.com/watch?v=Xim4Q258Mus