What do they look like?

Deer mice have small bodies. They weigh between 10 and 24 grams and they are typically 119 to 222 mm long, no longer than house mice. Tail length varies in different populations and ranges from 45 mm to 105 mm. Deer mice that live in woodlands are typically larger and have larger tails and feet than deer mice that live in prairies. Deer mice have round and slender bodies. The head has a pointed nose with large, black, beady eyes. The ears are large and have little fur covering them. The whiskers are long and prominent. Deer mice have shorter forelimbs than hind limbs.

Deer mice are grayish to reddish brown with white underparts. The fur is short, soft, and dense. The finely-haired tail is dark on top and light on the bottom, with a sharp division between the two colors. This differs from white-footed mice, where the separation of the two colors on the tail is less distinct. There are other characteristics that help distinguish deer mice from the similar white-footed mice. Deer mice generally have hind feet that are 22 mm or less, while white-footed mice usually have hind feet 22 mm or more. Also, deer mice are more richly colored with a brownish or tawny coat, whereas white-footed mice tend to be more pinkish-buff or grayish, with scattered dark hairs. These characteristics vary depending on location, however, and in some areas the two species are extremely hard to tell apart based on outward appearance.

Where in the world do they live?

Deer mice are common in North America. They are distributed from the northern tree line in Alaska and Canada southward to central Mexico. They are absent from the southeastern United States and some coastal areas of Mexico within this range.

What kind of habitat do they need?

Deer mice live in many different habitats throughout their range. They can be found in alpine habitats, northern boreal forest, desert, grassland, brushland, agricultural fields, southern montane woodland, and dry upper tropical habitats. Also, deer mice are found on boreal, temperate, and tropical islands. However, their most common habitats are prairies, bushy areas, and woodlands.

How do they reproduce?

Deer mice are polygynous, meaning that male deer mice each mate with more than one female.

Females deer mice can have many litters in a year. In the wild, reproduction may not occur during winter or other unfavorable seasons. Females are able to become pregnant again shortly after giving birth. The pregnancy of a female deer mouse that is not nursing young lasts from 22.4 to 25.5 days and the pregnancy of a female deer mouse that is nursing young lasts 24.1 to 30.6 days. Deer mice may have litters containing from one to eleven young with typical litters containing four, five, or six babies. Litter size increases each time a female deer mouse gives birth until the fifth or sixth litter and decreases afterwards.

Deer mice are very helpless at birth but develop quickly. At birth, each baby has a mass of about 1.5 g. The young are born hairless with wrinkled, pink skin, closed eyes, and folded over ears. Juvenile hair begins to develop on the second day after birth. On the third day, the ears unfold with the ear canal opening on the tenth day. Eyes open on the fifteenth day, and the young are weaned between day 25 and 35.

Deer mice can reproduce when they are 35 days old, but they usually breed for the first time at 49 days.

Like all female eutherian mammals, deer mice provide nourishment to their young before birth through the placenta. After the young are born, mother deer mice produce milk for their offspring. While nursing, the mother carries her young clinging to her nipples or one at a time in her mouth. Once weaned, the young usually leave the nest and become independent of their mother, although sometimes the mother will tolerate their presence for longer periods. Often when the mother has a second litter, she forces the first litter out of the nest.

How long do they live?

In captivity, deer mice can live as long as eight years. However, in the wild, life expectancy is much shorter, usually less than a year.

How do they behave?

Deer mice are most active at night. They spend most of their time on the ground but they are also adept climbers. Activity centers around a nest and food stockpile. Deer mice that live in prairies construct nests just below ground level in their own burrows or those abandoned by other animals. Forest dwelling deer mice construct nests near the ground in stumps, logs, brush piles, tree cavities, reconstructed bird nests, tree bark, or even cottages or outbuildings. Nests are made of rounded masses of plant matter (as much as 100 mm in diameter).

An adult male, a few adult females, and several young make up the basic social unit of the deer mouse. In the winter, groups of ten individuals or more of mixed sexes and ages may huddle together in nests to conserve heat. Also during winter, deer mice may enter a sluggish state called torpor to reduce body temperature and conserve energy.

Home Range

Home ranges of deer mice range from 242 square meters to 3000 square meters. Home ranges of males are larger than females and show more overlap. Males use their home ranges for both access to feeding and nesting and also to reproductive females. Females use their home ranges for feeding, nesting, and rearing young.

Females raising young are more aggressive in territory defense than males, and their territories overlap less, suggesting that they have more at stake in territory defense than males. Intruding deer mice will kill young that are unattended by a female.

How do they communicate with each other?

Deer mice have large eyes and ears as well as keen noses and long whiskers for perceiving their environment. They communicate by grooming one another, posturing with their bodies, producing scent, and making a variety of squeaky noises. Sometimes when disturbed they drum their front paws rapidly up and down against a hard surface. This may serve as a warning signal to other deer mice.

What do they eat?

Deer mice are omnivorous. They eat a wide variety of plant and animal matter depending on what is available, including insects and other invertebrates, seeds, fruits, flowers, nuts, and other plant products. Deer mice sometimes eat their own feces, a practice called coprophagy. In cooler climates, deer mice hide food in secret stockpiles during the autumn months.

What eats them and how do they avoid being eaten?

Deer mice are a staple in the diet of a wide variety of animals. Night-hunting predators, including snakes, owls, and various carnivorous mammals, are their biggest threat.

What roles do they have in the ecosystem?

Deer mice are important for spreading seeds of many types of plants and the spores of fungi. They are also an important food source for various predators.

Do they cause problems?

Deer mice eat seeds of valued forest trees, sometimes preventing the trees from growing back. In addition, deer mice can be destructive by raiding stored grains and other food supplies, gathering litter, and gnawing. Finally, deer mice are hosts for strain of hantavirus called Sin Nombre virus (also called Four Corners or Muerto Canyon virus). This virus, which can be transferred to humans from deer mice, causes an often deadly disease known as hantavirus pulmonary syndrome.

How do they interact with us?

Deer mice provide food for a number of carnivores, some of which are economically valuable fur-bearing mammals. Also, deer mice eat some insects that are considered pests.

Are they endangered?

Deer mice are abundant, often among the most abundant mice of certain areas. Densities can reach 11 mice per acre. Many factors including availablity of food, water, and nest sites are thought to affect how many deer mice can live in an area. However, only the availability of food has been studied in enough detail to show it has an effect on population density.

Some more information...

In Michigan, there are three distinct types of deer mouse. One of these is found only on Isle Royale. Another, the woodland deer mouse, is found in forests of the northern Lower Peninsula and the Upper Peninsula. The third, the prairie deer mouse, is found in open areas (preferably farm fields, early stages of grasslands, or along lake shores) of the Lower Peninsula and the southwestern Upper Peninsula. Woodland and prairie deer mice differ quite noticeably. Woodland deer mice have longer tails, ears, skulls, and hind feet than prairie deer mice. It is interesting that despite having overlapping ranges these types of deer mice do not interbreed. One possible explanation for this is the difference in their habitats, making it unlikely for them to meet.

Contributors

Allison Poor (editor), University of Michigan: February, 2005.

Andrew Bunker (author), University of Michigan: January, 2001.

References

Baker, R. H. 1983. Michigan Mammals. Wayne State Univerisity, Detroit, Michigan.

King, J. A. 1968. Biology of Peromyscus (Rodentia). First Edition. The American Society of Mammalogists, Stillwater, Oklahoma.

Kirkland, G. L. and Layne, J. N. 1989. Advances in the Study of Peromyscus (Rodentia). Texas Tech University Press, Lubbock, Texas.

LTER (Sevilleta Long-Term Ecological Research Project). 1998. University of New Mexico. http://sevilleta.unm.edu/data/species/mammal/profile/deer-mouse.html

Rowe, J. E., St. Jeor, S. C., Riolo, J., Otteson, E. W., Monroe, M. C., Henderson, W. W., Ksiazek, T. G., Rollin, P. E., and Nichol, S. T. 1995. Coexistence of several novel hantaviruses in rodents indigenous to North America. Virology 213 (1): 122-130.