Peromyscus maniculatus
(Deer Mouse)

Description:
The deer mouse has large ears, black, beady eyes, a distinctly bicolored tail and white feet. It occurs in two color phases, the back and sides can be gray or brown, and belly underneath is always white. Its tail is distinctly bicolored, gray or brown on top, and white underneath. Total length is 4 ¾ to 8 ¾ inches (119-22 mm), tail length is 1 ¾ to 4 ¾ inches (46-123 mm). It weighs 3/8 to 1 1/8 ounces (10-33 g).

Range:
Occurs in most of North America; absent in most of Alaska, northern Canada, and western and southeastern Mexico.

Habitat:
Being so widely distributed, it is found in a great variety of upland and riparian habitats, from open areas and brushlands to coniferous and deciduous forests. It is found in deserts, grasslands and woodlands. It also is attracted to human-built structures, cabins, sheds and even houses. It is commonly a pest in many rural human dwellings.

Diet:
Eats arthropods, other invertebrates, fruits, nuts, seeds, green plant material, and fungi. Insects, worms, and snails are most important in summer.

Ecology:
Deer mice are primarily nocturnal, and active throughout the year. They may store food. Their home range averages 2.5 acres (1 ha) or less, but may vary from a few hundred to a few thousand square meters, depending on circumstances. They exhibit territorial behavior during high population densities. population density is generally lowest in spring, highest in fall (sometimes up to about 30 per 2.5 acres (1 ha); densities as high as 109 per 2.5 acres (1 ha) and 163 per 2.5 acres (1 ha) have been reported. Idaho studies of effects of logging and grazing on small mammals show deer mice numbers were not affected by logging or grazing. Species is most abundant small mammal in most Idaho desert habitats, and most common mammal in Idaho. Being nocturnal, they are heavily preyed on by owls, (studies have shown that they can comprise almost half the food intake of owls), foxes and many other predators. Garter snakes seem to follow them into their nest burrows and consume the newborn mice. Considering their high reproductive potential, they obviously have a very high mortality rate due to predation and other factors. They do not hibernate and are active under the protective cover of snow during the winter. They do construct burrows, but also utilize burrows of other small mammals, and they even construct grass-lined nests on the surface of the ground in protective cover.

Reproduction:
Their reproductive potential is extremely high, but the breeding season is shorter in their northern range and at high elevations than elsewhere. Gestation lasts 23 days, and litter size averages 5 to 6 in their northern range, 4.5 in their southern range. Young develop rapidly; naked at birth, they grow fur and teeth in one week, and are weaned and become independent at about 4 weeks. Females produce 1 to 2 litters per year in the northern range, more in south. Young-of-year may attain sexual maturity by 2 months, or may not breed in some areas. Some litters are fathered by more than one male. With their high reproductive potential, it is theorhetically possible for one pair of deer mice to be ancestors of about 60 mice in 20 weeks. Obviously, their mortality is high.

Conservation:

Status:	Unprotected nongame species
Global Rank:	G5
State Rank:	S5

Important State References:
Groves, C.R. and B.L. Keller. 1983. Ecological characteristics of small mammals on a radioactive waste disposal area in southeastern Idaho. Amer. Midl. Natur. 109:253-265.