The species has 56 subspecies. They are all tiny mammals that are plentiful in number. The deer mouse is a small rodent that lives in the Americas and is closely related to the white-footed mouse, Peromyscus leucopus. Because the two species are extremely similar in appearance, they are best distinguished through red blood cell agglutination tests or karyotype techniques. The deer mouse can also be distinguished physically by its long and multicolored tail. Deer mice are very often used for laboratory experimentation due to their self cleanliness and easy care.
The deer mouse is small in size, only 3 to 4 inches (8 to 10 cm) long, not including the tail. They have large beady eyes and large ears giving them good sight and hearing. Their soft fur can vary in color, from white to black, but all deer mice have a distinguishable white underside and white feet.
Deer mice are nocturnal creatures who spend the day time in areas such as trees or burrows where they have nests made of plant material. The pups within litters of deer mice are kept by the mother within an individual home range. The deer mice do not mingle in groups with their litters. During the development stages, the mice within one litter interact much more than mice of two different litters. Although deer mice live in individual home ranges, these ranges do tend to overlap. When overlapping occurs, it is more likely to be with opposite sexes rather than with the same sex. Deer mice that live within overlapping home ranges tend to recognize one another and interact a lot.
Deer mice can reproduce throughout the year, though in most parts of their range, they breed from March to October. Deer mouse breeding tends to be determined more by food availability rather than by season. In Plumas County, California, deer mice bred through December in good mast (both soft and hard masts) years but ceased breeding in June of a poor mast year. Deer mice breed throughout the year in the Willamette Valley, but in other areas on the Oregon coast there is usually a lull during the wettest and coldest weather. In southeastern Arizona at least one-third of captured deer mice were in breeding condition in winter. In Virginia breeding peaks occur from April to June and from September to October.
Female deer mice construct nests using a variety of materials including grasses, roots, mosses, wool, thistledown, and various artificial fibers. The male deer mice are allowed by the female to help nest the litter and keep them together and warm for survival.
In a study, less than half of both male and female deer mice left their original home range to reproduce. This means that there is intrafamilial mating and that the gene flow among deer mice as a whole is limited.
There have been recent studies that reveal deer mice also have OCD-like behaviors from altered gut microbiota. This phenomenon is typically shown in their abnormally large nest sizes and the behavior is present within 8 weeks of birth. Large nest building is considered to be a maladaptation as these mice are unnecessarily investing extra energy and effort in building larger nests in a laboratory where conditions are stable.
Gestation, litter size and productivity
Deer mice reproduce profusely and are highest in numbers among their species compared to other local mammals. Peromyscus species' gestation periods range from 22 to 26 days. Typical litters are composed of three to five young; litter size ranges from one to nine young. Most female deer mice have more than one litter per year.[Three or four litters per year is probably typical; captive deer mice have borne as many as 14 litters in one year. Males usually live with the family and help care for the young.
Development of young
Deer mice pups are altricial, i.e. born blind, naked and helpless; development is rapid. Young deer mice have full coats by the end of the second week; their eyes open between 13 and 19 days and they are fully furred and independent in only a few weeks. Females lactate for 27 to 34 days after giving birth; most young are weaned at about 18 to 24 days. The young reach adult size at about 6 weeks and continue to gain weight slowly thereafter.
Age of first estrus averages about 48 days; the earliest recorded was 23 days. The youngest wild female to produce a litter was 55 days old; it was estimated that conception had occurred when she was about 32 days old.
Deer mouse pups usually disperse after weaning and before the birth of the next litter, when they are reaching sexual maturity. Occasionally juveniles remain in the natal area, particularly when breeding space is limited. Most deer mice travel less than 152 m (499 ft) from the natal area to establish their own home range.
Longevity and mortality
In the lab their maximum life span is 96 months, and mean life expectancy is 45.5 months for females and 47.5 for males. In many areas deer mice live less than 1 year. O'Farrell reported that a population of deer mice in big sagebrush/grasslands had completely turned over (e.g., there were no surviving adults of the initial population) over the course of one summer. One captive male deer mouse lived 32 months, and there is a report of a forest deer mouse that lived 8 years in captivity (another mouse was fertile until almost 6 years of age).
Peromyscus maniculatus are found in places including Alaska, Canada, and parts of South America. The majority of deer mice nest high up, in large hollow trees. The deer mouse nests alone for the most part but will sometimes nest with a deer mouse of the opposite sex. They are populous in the western mountains and live in wooded areas and areas that were previously wooded. The deer mouse is generally a nocturnal creature. Deer mice can be found active on top of snow or beneath logs during the winter seasons.
Deer mice inhabit a wide variety of plant communities including grasslands, brushy areas, woodlands, and forests. In a survey of small mammals on 29 sites in subalpine forests in Colorado and Wyoming, the deer mouse had the highest frequency of occurrence; however, it was not always the most abundant small mammal. Deer mice were trapped in four of six forest communities in eastern Washington and northern Idaho, and they were the only rodent in ponderosa pine (Pinus ponderosa) savanna. In northern New England deer mice are present in both coniferous and deciduous forests. Deer mice are often the only Peromyscus species in northern boreal forest. Subspecies differ in their use of plant communities and vegetation structures. There are two main groups of deer mouse: the prairie deer mouse and the woodland or forest deer mouse group.
Deer mice are omnivorous; the main dietary items usually include seeds, fruits, arthropods, leaves, and fungi; fungi have the least amount of intake. Throughout the year, the deer mouse will change its eating habits to reflect on what is available to eat during that season. During winter months, the arthropods compose of one-fifth of the deer mouse's food. These include spiders, caterpillars, and heteropterans. During the spring months, seeds become available to eat, along with insects, which are consumed in large quantities. Leaves are also found in the stomachs of deer mice in the spring seasons. During summer months, the mouse consumes seeds and fruits. During the fall season, the deer mouse will slowly change its eating habits to resemble the winter's diet.