Winter 2000

[TEXT ARCHIVE WEB-PUBLISHED MARCH 2002.
ORIGINAL PRINT PUBLICATION DATE: WINTER 2000.]

White-footed mice: Home Recyclers

By Sheryl De Vore

Last summer, a gray catbird built its nest in a shrubby woodland. But this winter, a different creature lives in the seemingly abandoned nest. On a brisk winter hike, you may walk right by an old bird's nest, not even knowing the life that may be brimming inside — a large-eyed, big-eared, brown-backed 1-2-inch long animal with snow-white underparts and feet, and long, thin tail. It's called the white-footed mouse .

The white-footed mouse (Peromyscus leucopus) dwells mostly in woodlands, river bottoms, and shrubby areas. An acrobat on tiny feet, this mouse can climb on trees and shrubs where it creates a dome of plant materials, feathers, and down on top of an old bird's nest. Snuggled inside, the white-footed mouse can survive and even bear young during cold winters.

The white-footed mouse and its close relative, the deer mouse, look nearly identical, although if placed side by side the deer mouse is often slightly smaller, with a shorter tail. Neither hibernates in winter and both are active at night. But they live in different places.

You won't find a deer mouse (Peromyscus maniculatus) in a tree or shrub. This species doesn't climb. Instead it lives mostly in grasslands where it builds a burrow one to 12 inches below the soil. There it keeps warm and raises young.

Because so much of Illinois' grasslands have been lost, deer mice numbers are declining statewide. The white-footed mouse, which also lives in hollow logs, stump holes, thickets, and underground burrows, may be more adaptable.

Both serve as important food sources for owls, weasels, foxes, and other animals. In fact, says Steven D. Bailey, an owl expert and ornithologist with the Illinois Natural History Survey, "the northern saw-whet owl, a Chicagoland Wilderness winter visitor, relies to a great extent on white-footed mice for its food." Bailey said in a recent analysis of saw-whet owl pellets, "the contents all had remains of the leucopus species."

Deer and white-footed mice get nicely fattened for their predators by eating plant seeds, including those from oak and hickory trees. The omnivorous rodents also eat insect larvae, spiders, and centipedes. They spend hours at night eating and eating. Small rodents need more food in proportion to their weight than do larger warm-blooded animals because it's hard for the little guys to conserve heat. They need a zippy metabolism to produce the extra warmth that counteracts the effects of a small body-to-surface-area ratio.

Some winter evening, when you are outside in a quiet woods, listen for soft scratching on a tree trunk or in leaf litter, as well as a quiet musical buzz. You're hearing a white-footed mouse searching for his midnight snack or singing, perhaps, for his supper.

Mice and Disease

Lyme Disease
Lyme disease, a serious condition affecting various body tissues, is transmitted by deer ticks. In its early stages it is manifested as a skin rash, but it can also spread to the joints, nervous system, and to other organ systems in its later stages. White-footed mice can be hosts of the disease, transmitting it to the ticks which, when they become adults, can transmit it to humans. The Illinois Department of Public Health reports that the incidence of Lyme disease in the state has been declining since 1991. In some instances, Illinois residents probably got the disease in another state and came home with it. Health officials recommend wearing long-sleeved shirts, long pants, and tucking pants legs into one's socks when walking through grassy areas. For more information, see the American Lyme Disease Foundation, Inc.

Hantavirus
Hantavirus pulmonary disease can be fatal. It is transmitted by breathing or touching rodent feces, including those of the white-footed mouse. However, it is not transmitted via rodent bites. Hantavirus causes flu-like symptoms including fatigue, fever, and muscle aches; later symptoms include coughing and shortness of breath. Pat Piercy of the Illinois Department of Public Health said Illinois has only had one confirmed fatal case of hantavirus. Of 70 mammals trapped near where the victim lived, 61 were the white-footed mice and seven tested positive for the disease. Bottom line is not to dig into or sniff rodent burrows. For more information: www.cdc.gov/ncidod/diseases/hanta/hpsr.