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Scientific name: Peromyscus leucopus
Common name: 
White Footed Mouse

Information in this Species Page was compiled by Bill Mentecky  in Biology 220W, Spring 2000 and Emily Morse in Biology 220M, Spring 2002 at Penn State New Kensington.

The white footed mouse is an extremely common and locally abundant organism (four to fifteen individuals per acre) that is found in almost any brushy or wooded habitat from southern Canada throughout the continental United States. The seventeen sub-species of P. leucopus differ in their specific habitats of choice but all are adapted to a semi-arboreal life (they are excellent climbers!) and all seem to prefer densely vegetated sites within which they find cover and protection adjacent to open fields within which they forage for food. Deciduous forests with adjacent brushy fields support the highest densities of white footed mice. The white footed mouse has been described as the “most successful mammal in Pennsylvania” because of its wide spread occurrence and ability to flourish in so many different habitats.

Nests
Their nests are typically very well hidden and are established in a great variety of specific locations: in old logs, tree stumps, abandoned bird’s nests, squirrel’s nests, chipmunk burrows, woodchuck burrows, etc. They can also enter human dwellings and make their nests in attics, chimneys or basements. Nests are lined with gathered grasses, hair, leaves, feathers, milkweed silk, moss, and many types of human-made materials. If the nest becomes too full of wastes, it is abandoned and replaced with another.

Appearance
Adult white footed mice are between sixteen and twenty centimeters long (up to ten of these centimeters are the mouse’s tail). They weigh between ten and forty three grams. They have large ears covered with tufts of hair, large brown eyes, and a variety of body colors that range from brown to reddish (the summer dominant color) to gray (the winter dominant color). Usually, the sides of the mouse are a bit darker than the back and the head. They also typically have a dark line running down the middle of their backs and white fur on their bellies, ankles, and feet (hence, their names!).

Diet
The white footed mouse is a prodigious consumer of a wide range of types of seeds. It can eat up to 30% of its body weight per day, and uses its excellent sense of smell to actively locate, gather, and sequester seeds and other plant materials. Their diet varies with location and season. They eat grasses, acorns, beechnuts, hickory nuts, mushrooms, corn, fruit, chestnuts, jewel weed seeds (which stain their stomachs a turquoise blue!), and pine and cherry seeds. They also opportunistically feed on beetles, snails, grasshoppers, caterpillars (they are a major predator of gypsy moth caterpillars!), crickets and flies. They hunt and pounce on their prey much like a cat. They also feed on road kills and other sources of carrion. During the fall, the white footed mouse caches and sequesters huge quantities of collected food in a variety of locations. Quarts of seeds and nuts have been collected from their nests. The mouse uses its expandable cheek pouches to carry and transfer the seeds and nuts to their nests and other cache sites.

Reproduction
In northern regions, breeding peaks in the spring and again in the fall. In the southern regions, breeding is year round. A white footed mouse is sexually mature at eight or ten weeks of age. The gestation period is between twenty-one and twenty-seven days. Typical brood sizes are three to five young and females have three to four litters per year. The female cares extensively for the young and the males (at least under laboratory conditions) may also play a role in rearing and nurturing the litter.  The potential life span of the white footed mouse is eighteen months to two years in the wild, but the actual rate of predation on the mice is so intense that nearly the entire population of a site is replaced every year.

The white footed mouse does not hibernate but, instead, enters a state of deep sleep in its food-filled nest especially on the coldest winter nights. It is able, though, to leave its nest on warmer nights to gather food from its scattered caches.  

Population Growth and Controls; Health Risk to Humans
The white footed mouse is a preferred prey species for a long list of avian, mammalian and reptilian predators. Snakes, weasels, and owls are the principle consumers of the mice, but almost any carnivore (including shrews, skunks, coyotes, bobcats, foxes, hawks, house cats, humans and even wood ducks) can and will eat them. In ecosystems lacking sufficient numbers of predators, the white footed mouse can become an overly abundant and extremely destructive pest.

The white footed mouse can be a problem species when their numbers grow beyond the limits and controls of its ecosystem. Overpopulation can lead to excessive consumption of seeds and cause inhibition of plant germination and dispersal. The efficiency of the white footed mouse in gathering seed is one the main reasons that forest re-planting must employ the more time consuming and expensive method of seedling plantings rather than simpler tree-seed broadcasting methods.  Invasion of stored grain products and the barns and houses of humans also can lead to explosive growth rates and unacceptable population levels of this mouse. The white footed mouse is also a carrier of the bacterium that causes Lyme’s Disease (which is transferred by the very small “deer” tick) and the Hantavirus (which is transmitted via an infected mouse’s saliva, urine, or feces) which causes a serious respiratory illness in humans.

Benefits
The benefits of the white footed mouse are also considerable. Their consumption of insects and especially several economically destructive species (like the spruce sawfly and the gypsy moth) help to maintain numerous potential pests at environmentally acceptable levels. The activity of the mice in digging nests and caches helps to loosen and aerate soil, and their caching of seeds, which are not always then consumed, may actually represent a major vector of seed dispersal for many plant species. The mice also serve as a “buffer” food that acts to reduce predation pressure on other, more “desirable” game animals, and fundamentally, the abundance of the mice and their very rapid rates of reproduction provide a renewable food source for many of the dynamic and interesting predator species of our North American ecosystems.



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