White-footed mice seek a cozy, warm home
December 30, 2024 | By Susan Shea | The Outside Story
Illustration by Adelaide Murphy Tyrol
During winter, I often hear gnawing and the scurrying of little feet inside the walls of our house. Mice have taken shelter in our old farmhouse again.
Although I hate killing the cute creatures, after we had to hire a carpenter twice to remove sections of our walls and take out smelly mouse nests, we resorted to trapping them, since our cats couldn’t get at the mice inside the walls. We began with live traps, but the mice just returned, so now we use snap traps.
Our traps have revealed that we’ve been sharing our house with white-footed mice (Peromyscus leucopus). These mice have reddish-brown bodies with a black stripe on the middle of the back and a white belly and feet. The furred tail is usually shorter than the body. The deer mouse, a close cousin to the white-footed mouse, has a longer tail and less black on the back, but individuals can vary. These two northeastern species can be difficult to tell apart – especially when they are scampering through your house.
White-footed mice are good climbers, which comes in handy for running along pipes in house basements, including ascending vertical pipes. However, when they are not living in country homes and barns, white-footed mice inhabit deciduous forests, brushy areas, and fields, using their climbing ability to nest in trees. These mice also build nests in stone walls, under stumps and logs, and in old bird and squirrel nests. I’ve also found mouse nests in birdhouses and firewood piles. The spherical nest is 8 to 12 inches in diameter and is made of dried grasses, leaves, and moss. (In our house, they used chewed-up insulation.) The mice line the interior cavity with soft bedding such as milkweed fluff, fine shredded bark, hair, and feathers.
White-footed mice use underground runways dug by other small mammals, including those in the subnivean zone between the ground and the bottom of the winter snowpack. They communicate with other mice through scent-marking, calls, and drumming their feet. They are active at night all winter but sometimes go into torpor during the day, reducing body temperature and metabolism to conserve energy.
These mice are omnivorous and feed on seeds, nuts, small fruits, vegetation, insects, caterpillars, and even carrion. They are predators of invasive spongy moth pupae (formerly called gypsy moth), which is a benefit to the forest. Mice store food for later use. We have found stashes of sunflower seeds in various corners of our house, brought in from our winter bird feeder. When I pulled my book on mammals out of the bookcase to research this article, there were sunflower seed shells on top!
One of the reasons we have a mouse-in-the-house problem is that they are prolific breeders. Female white-footed mice can breed at six to seven weeks and have two to four litters per year with three to seven young in each litter. That adds up to a lot of mice!
Though they may be household pests, white-footed mice play important ecological roles in their natural habitat. They are prey for many other animals, including owls, hawks, foxes, coyotes, bobcats, and snakes. Like some other small mammals, these mice help disperse mycorrhizal fungi throughout the forest. When mice consume mushrooms and underground truffles, the fungal spores pass through their guts and are deposited in new areas via their scat. These fungi are essential to forest health, colonizing tree roots and aiding in water and nutrient absorption.
While the white-footed mouse is more common at low elevations, the deer mouse often lives in coniferous forests and at higher elevations in our region. Deer mice are better adapted to colder temperatures, and their range extends across Canada below the subarctic. However, recent research indicates that the white-footed mouse is expanding its range northward into southern Quebec as the climate warms, sometimes displacing the deer mouse. Other studies have found that the two species can co-exist in the same forest. They appear to minimize competition by frequenting different microhabitats and choosing different types and sizes of seeds.
Although we’ll need to continue the battle with mice living in our house, I don’t blame them for preferring its warmth and protection to living outdoors in the cold and evading predators. What we really need is a resident weasel or snake to help us!
Susan Shea is a naturalist, writer, and conservationist based in Vermont. The Outside Story is assigned and edited by Northern Woodlands magazine and sponsored by the Wellborn Ecology Fund of New Hampshire Charitable Foundation.