The cinereus shrew or masked shrew (Sorex cinereus) is a small shrew found in Alaska, Canada, and the northern United States. 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 that is brown on top and pale underneath with a dark tip. Its body is about in length including a long tail. It weighs about . It has darker colouring than other shrews. Masked shrews can live up to two years, but, on average, only survive eighteen months. In a long-term study done in Alaska, Yom-Tov and colleagues (2005) found that the masked shrew's body size contradicts Bergmann's Rule. The study, done on 650 specimens and spanning from 1950 to 2003, examined body size in relation to ambient temperature. Measurements of body weight and the length of the tail, ear, hind foot, and body were taken. Results yielded that the masked shrew's body size decreased with high latitudes and with lower mean January temperatures, a trend that opposed Bergmann's Rule. It was suggested that this may be a coping mechanism to limit total energy requirements due to decreased food availability in winter months. Additionally, it was shown 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 shrew's main diet. Distribution The masked shrew is the most widely distributed shrew. 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, foxes, leopard frogs, bluebirds, brown trouts, and weasels. Masked shrews are susceptible to many types of parasites, like fleas and tapeworms. Cowan and colleagues (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