Occurs from Alaska/Canadian Arctic tundra through Rockies, northern Great Plains, and Appalachians.
The masked shrew's head and neck are evenly grayish to brown above and paler underneath. Its tail is fairly long and bicolored. Total length is 3.5 to 4.4 inches (87-110 mm), tail length is 1.4 to 1.6 inches (35 to 40 mm), its weight is only 0.10 to 0.20 ounce (3-6 grams).
It seems to prefer coniferous forests and moist habitat along streams and ponds. Thick leaf litter in damp forests may also represent favored habitat, although the species appears adaptable to major successional disturbances. In Idaho, it can be found in both wet and dry coniferous forests, and even occasionally in sagebrush. In Wyoming they have been found from 3800 to 9450 feet.
They eat insects and other invertebrates, carrion, small vertebrates, and, occasionally, seeds. They consume their own weight in food each day.
This species remains active throughout day (and year) to secure enough food to maintain a high metabolic rate. They may use echolocation to detect prey. Its peak activity period occurs from 0100-0200 hr. One study found that activity seemed to correspond to weather, increasing when the temperature of the previous night increased and decreasing when the temperature decreased. There is a big surge in activity immediately after rain, especially if it occurs between 6:00 pm and midnight. Their population size is subject to large annual fluctuations. Density estimates range from 1 to 12 shrews per 0.4 ha.(1 acre). Home range is about 0.04 ha (0.1 ac). They are usually found in scattered, locally abundant populations. Individuals rarely live past second summer.
Breeding season may last from March-September (in Nova Scotia, evidence of mid-winter births exists for at least some years). Females produce 2 to 3 litters. Gestation lasts 18 days. Litter size varies from 2 to 10 young, but averages 7. Young are weaned in 3 weeks, and reach sexual maturity in 20 to 26 weeks.
|Status:||Unprotected nongame species|
Important State References:
Rickard, W.H. 1960. The distribution of small mammals in relation to climax vegetation mosaic in eastern Washington and northern Idaho. Ecology 41: 99-106