In warm regions, reproduction may occur more or less year-round in some species. More typically, breeding occurs from spring until fall with a summer lull. This is especially true in cooler climates. Litter size varies from 1 to 8 young, but is usually 3 to 5. Females may have from 2 to 4 or more litters per year, depending on species and climate.
During the breeding season, female white-footed and deer mice come into heat every fifth day until impregnated. The gestation period is usually 21 to 23 days, but may be as long as 37 days in nursing females. Young are weaned when they are 2 to 3 weeks old and become sexually mature at about 7 to 8 weeks of age. Those born in spring and summer may breed that same year.
Mated pairs usually remain together during the breeding season but may take new mates in the spring if both survive the winter. If one mate dies, a new one is acquired. Family groups usually nest together through the winter. They do not hibernate but may become torpid for a few days when winter weather is severe.
Nests consist of stems, twigs, leaves, roots of grasses, and other fibrous materials. They may be lined with fur, feathers, or shredded cloth. The deer mouse often builds its nest underground in cavities beneath the roots of trees or shrubs, beneath a log or board, or in a burrow made by another rodent. Sometimes deer mice nest in aboveground sites such as a hollow log or fencepost, or in cupboards and furniture of unoccupied buildings.
White-footed mice may use abandoned bird or squirrel nests, adding a protective “roof” of twigs and other materials to completely enclose a bird’s nest. Like deer mice, they nest at or just below ground level or in buildings.
Family groups of white-footed mice usually nest together through the winter, as do family groups of deer mice. They do not hibernate but may become torpid for a few days when winter weather is severe.White-footed mice spend a great deal of time in trees.
The deer mouse occupies nearly every type of habitat within its range, from forests to grasslands. It is the most widely distributed and abundant mammal in North America.
The white-footed mouse is also widely distributed but prefers wooded or brushy areas. It is sometimes found in open areas.
The other species of Peromyscus have somewhat more specialized habitat preferences. For example, the cactus mouse occurs in low deserts with sandy soil and scattered vegetation and on rocky outcrops. The brush mouse lives in chaparral areas of semi-desert regions, often in rocky habitats.
White-footed and deer mice are primarily seed eaters. Frequently they will feed on seeds, nuts, acorns, and other similar items that are available. They also consume fruits, insects and insect larvae, fungi, and possibly some green vegetation. They often store quantities of food near their nest sites, particularly in the fall when seeds, nuts, or acorns are abundant.