Subfamily: Sigmodontinae (includes deer mice, harvest mice, grasshopper mice, woodrats, cotton rats)
Deer mice are the prototype for "field mice" with large, bulging eyes, big ears, a bicolored pattern and a long tail. They are larger than the harvest mice (Reithrodontomys), but noticeably smaller than woodrats (Neotoma) and cotton rats (Sigmodon). The deer mouse is about 148-200 mm (seven in.) long, including the tail. The bicolored tail is less than 90% of the head and body length; this distinguishes the deer mouse from the high desert piñon mouse (P. truei), which has a tail over 90% of the head and body length.
The deer mouse coloration is described as "bicolored", meaning it has a distinctly darker upper body coloration compared to the white undersides. The body color varies from a yellowish or reddish brown to grayish above, with pure white undersides and feet. The bicolored body and distinctive large ears distinguish the deer mouse from the introduced house mouse (Mus musculus), which is uniformly gray. The house mouse is found in city and urban areas while the deer mouse prefers natural habitats. You can get either where development pushes against undeveloped lands.
Range and Habitat
Deer mice are commonly found in California and Mexico. Throughout their range, they are found in nearly all ecological communities and life zones from the desert floor to the high mountains. They can be highly abundant, numbering as many as ten per acre.
Behavior: Deer mice live up to five years, longer than any other species of small rodent (most mice live for only a year). A nocturnal species, they are very energy efficient, reducing their body temperature when in their burrows. Lowering their metabolism means they need less food. Deer mice do not hibernate during the winter.
Reproduction: Deer mice breed during the spring, and fall, and to some extent midsummer. Females can have up to four litters per year with an average of three to six young per litter. The gestation period is from 22 to 25 days long. Deer mice do not burrow but build their nest from grasses in protected areas above ground beneath debris, in tree cavities, in rotting logs, or in abandoned burrows.
Young mice may remain with the mother for sometime after they are weaned. Although deer mice establish home ranges, there is not an aggressive defense of a home territory. Home ranges are from three-quarters to ten acres in size and are shared with breeding animals of both sexes and a few immature individuals.
Diet: Food selection is dependent on both habitat and season. Deer mice feed heavily on larvae from lepidopterans (includes moths and butterflies) and other insects in the spring. They can eat large volumes and are capable of ridding an area of many insects that may be detrimental to trees. In the fall, seeds become a major food source and are stored in caches for use during the winter.
Because of their abundance, deer mice are a major food source for almost every bird and mammal predator. When the predators are reduced or absent, the mice can become pests.
No other group of mammals shows more variation that the genus Peromyscus. P. maniculatus has a range from central Alaska to the mountains south of Mexico City and from the Pacific Ocean to Labrador, on the Atlantic Ocean. In an area over five million square miles with a wide variety of habitats, evolution has differentiated the species into 60 different forms with varying degrees of distinctness. Many characteristics appear to be the result of environmental selection, such that dark forms are found on humid dark soils, on the top of isolated desert mountains, and on lava flows, with pale forms found in the desert. Refer to Mammals of the Pacific States by L. G. Ingles for a more in-depth discussion of these differences.
In the San Diego region, deer mice may be carriers of Hantavirus. When present, this virus is spread through the rodent's urine and feces. Although the mice do not become ill from the virus, humans can become infected when they are exposed to contaminated dust from the nests or droppings. We are advised not to camp or sleep where mouse droppings are abundant, and to clean indoor areas where they live using appropriate precautions.
Cornett, James W. 1982. Wildlife of the Western Mountains. Nature Trails Press. Palm Springs, California.
Ingles, Lloyd G. 1965. Mammals of the Pacific States. Stanford University Press. Stanford, California.
Jameson, E. W., Jr., and H. J. Peeters. 1988. California Mammals. University of California Press, Berkeley, California.
Wilson, Don E., and D. M. Reeder, eds. 1993. Mammal Species of the World. Smithsonian Institution Press, Washington, D.C.
Wilson, Don E., and F. Russell Cole. 2000. Common Names of Mammals of the World. Smithsonian Institution Press, Washington, D.C.