The Mighty Montana Deer Mouse

By Diane Tipton, Montana Fish, Wildlife & Parks

Friday, October 05, 2007
Comprehensive Fish & Wildlife Conservation Strategy (CFWCS)

This article was Archived on Monday, November 05, 2007

While Montana’s much admired big game species get all the attention this hunting season, deer mice are everywhere, busily preparing for winter.

Why should we care? Deer mice are small but mighty. These mice, weighing in at about half the weight of a penny at birth, are an important food source for many of the animals Montanans like to watch in the outdoors. Hunters need not tune out, deer mice are also key to post-fire propagation of bitter brush, an   important forage for deer and elk, after wild land fires.

The little heralded deer mouse has brown deer-colored fur that may vary from brown to gray-brown on top with a white underside. Its tail is furred, darker on top and lighter underneath. They feed on the larvae of moths and butterflies and other insects in spring. To prepare for winter, they gain weight and collect and store seeds, though they don’t hibernate.

These natives live up to five years, longer than any other species of small rodent, and they inhabit most areas of Montana. Females may have four litters of three to six young in a year.

Because they are widespread, long lived, and productive, they provide an abundant food source for most predatory birds and mammals including foxes, coyotes, bobcats badgers, snakes and owls. In this way alone, deer mice support the health and reproduction of many species. But that’s not all.

Biologists say deer mice help to propagate bitterbrush, nutritious forage for deer and elk with 57 percent digestible protein.   The seeds for bitter brush propagation need to be scarified or have a layer scratched off of them and that is what the mice do naturally with their teeth as they collect and cache the seeds. Seeds cached by deer mice are also at the optimum depth for sprouting, about 1.3 cm. According to the College of Agriculture and Bioresources at the University of Saskatchewan most bitterbrush seedlings that emerge successfully after fires are those in caches made by rodents.

When seeds or insects are artificially planted, deer mice are among the rodents most likely to eat them. For example, when humans plant bitter brush seeds deer mice will collect them for food. Recent research in Montana suggests the release of gall flies to fight spotted knapweed may also increase the food supply for deer mice.

Though deer mice make the outdoors a more opportune place for their fellow creatures, they are not universally appreciated. Some deer mice may carry an infection that, if transmitted to humans, causes hantavirus pulmonary syndrome.

However, Rick Douglass, professor of biology at Montana Tech in Butte, who has studied the role of deer mice in the transmission of hanta virus extensively, does not recommend trapping or poisoning local deer mice. Removing resident mice creates a "population sink" he said that attracts new mice on the move from other locations. These mobile mice are more likely to have contracted the virus than a stable, resident population of deer mice with an established territory.

For more on deer mice, see the Montana Field Guide   on the Montana Fish, Wildlife and Parks home page at   fwp.mt.gov   .

For more information on interdependent wildlife communities, see the state’s Comprehensive Wildlife Plan on the FWP web site on the Wild Things page.