Mammals of Mount Rainier National Park

by Merlin K. Potts; Russell K. Grater

THE MEADOW MICE

Three species of meadow mice are known to inhabit the park, and of these, two are so similar that the positive field identification of each is difficult in most instances. Only the Cascade meadow mouse, or water vole, shows sufficiently distinctive characteristics to permit easy recognition. Of the two similar species, the Oregon meadow mouse is probably most likely to be encountered.

The Oregon meadow mouse, Microtus oregoni oregoni (Bachman), is similar in general coloration to the Olympic meadow mouse, but has conspicuous ears, is distinctly smaller, and has been found from park boundaries to 5,000 feet and higher.

The Olympic meadow mouse, Microtus longicaudus macrurus Merriam, is dark brown above, with slightly paler sides, and with under parts a dull buff or whitish. The tail is distinctly bicolor, black or brown above, white below. The ears are inconspicuous. The head and body measure about five and one-quarter inches, the tail about three and one-half inches. This mouse is rarely found above the 3,000 foot elevation.

The Cascade meadow mouse, Microtus richardsonii arvicoloides (Rhoads), is much larger than any of the other species found in the park. The head and body measure about six inches, the tail a little over three inches in a typical specimen. In general this species prefers a moister habitat than the other meadow mice, and is usually found from 4,000 feet to forest line (6,500 feet). It is the most abundant of the park mammals found at high elevations, and has been recorded at Camp Muir, 10,000 feet.

Specimens in park collection: Oregon meadow mouse, RNP-27, RNP-32, RNP-51, RNP-71; Olympic meadow mouse, RNP-31; Cascade meadow mouse, RNP-5, RNP-26, RNP-48, RNP-49, RNP-50, RNP-59, RNP-60, RNP-75, RNP-81, RNP-109; Longmire Museum, Park Headquarters.

As the name implies, the general habitats of these rodents are the open parks and meadows, from park boundaries to above the forest line. They are locally abundant in many places, and are active throughout the year, feeding upon the various green and succulent plants, burrowing along the surface of the ground beneath the snow to find food in winter. Only the Cascade meadow mouse shows any marked deviation in its habits, being semi-aquatic, at least in summer, with a marked preference for marshy or boggy meadows, taking to the water readily to escape danger, and burrowing along the banks of small streams. In winter this mouse often seeks the hillsides and normally dryer sites, probably in search of a more abundant food supply, the change in habitat being encouraged by abundant winter moisture. These hillside habitats often reveal earthen tunnels on the ground surface as the snow melts, similar to those made by the pocket gopher. Mounds of earth thrown up around the burrows of the Cascade meadow mouse are also similar to the gopher mounds, but may be distinguished from the latter by the open burrows, often left so, rather than being closed by earthen plugs.

It is well that the meadow mice are so abundant and prolific, since they constitute a large portion of the food supply of coyotes, foxes, and other predators.

MOUNTAIN LEMMING MOUSE, OLYMPIC PHENACOMYS, HEATHER VOLE
Phenacomys intermedius oramontis Rhoads

The lemming mouse is similar in appearance and habits to the meadow mice; the head and body are four and one-half inches to five inches long; the tail from one to one and one-half inches. The back is a grizzled gray-brown, showing a yellowish tinge; the belly is gray-white; the fur is sprinkled with black hairs. The dull color and short tail distinguish this mouse from all others except the Oregon meadow mouse. The latter is slightly smaller, the hair is less woolly, but field distinction is difficult or impossible.

Specimens in park collection: None.

The genus Phenacomys is found in the western United States and most of Canada, inhabiting the mountain summits and colder zones.

The Olympic phenacomys of Mount Rainier occurs only at the higher elevations, 4,500 to 8,500 feet in the park, and its range extends into the Olympic Mountains, as well as southward along the Cascade crest into central Oregon.

The alpine parks and windswept slopes well above forest line are the home of the hardy little lemming mice. One of the common names for the animal, heather vole, is suggestive of the locality where they may be found, finding shelter in the protection afforded by the low-growing masses of the heather. Their range is not entirely confined to the alpine country, however, since records have been established in the upper forested areas, down to a low elevation of 4,000 feet.

The only conspicuous evidences of the presence of the heather vole are the tidy, compact winter nests of dried grass, lichen, and other plant fibers. These nests, constructed on the ground under the snow, are apparently abandoned when the snow melts, and it is difficult to discover other signs of the animal’s activities.

Like the meadow mice, the mountain lemming mouse is a staple item in the diet of the predators.

CASCADE RED-BACKED MOUSE
Clethrionomys gapperi cascadensis Booth

The red-backed mouse is slightly larger than a house mouse; in a typical specimen the head and body are about four inches long, the tail slightly less than two inches. The distinguishing characters which separate this animal from the other mice are the broad, reddish-brown stripe over the back from the forehead to the base of the tail (this stripe distinguishes it from the held mice), and the inconspicuous ears and short tail which are so different from the large ears and long tail of the white-footed mouse.

Specimens in park collection: RNP-17, RNP-62, RNP-63, RNP-65, RNP-66, RNP-67, RNP-68, RNP-69; Longmire Museum, Park Headquarters.

The many species of red-backed mice occur generally over the wooded sections of North America.

The Cascade red-backed mouse is found in the Cascade Mountains from British Columbia southward into Washington, east into northern Idaho and northeastern Oregon. In Mount Rainier National Park it occurs generally from park boundaries to forest line.

The heavily wooded areas of the park are the preferred habitats of the red-backs. They are usually common in such localities, but are not locally abundant in colonies, as are the field mice.

The activities of these mice are not confined to nocturnal excursions. They may be seen at any time of day, and the quiet observer in the deep woods is almost certain to glimpse them if he is patient enough to watch for a few moments.

NORTHWESTERN JUMPING MOUSE
Zapus princeps trinotatus Rhoads

The Northwestern jumping mouse is a little larger than a house mouse, head and body about four inches, tail about six inches. The back is dark, sprinkled with buff; a broad band of buff, sprinkled with blackish hairs, extends along the sides; the underparts are pure white. The long tail is dull gray above, white below, and almost naked except for a tiny tuft of dark hair at the tip. This mouse may be easily distinguished from any other park animal by the long hind legs and tail.

Specimens in park collection: RNP-6, RNP-24, RNP-25, RNP-52, RNP-53, RNP-54, RNP-58, RNP-73, RNP-76, RNP-92; Longmire Museum, Park Headquarters.

The jumping mice are found throughout most of the United States from northern California and North Carolina, northward into Canada to the Arctic Circle. The Northwestern jumping mouse occurs from northern California through the Cascades to the coastal region of southern British Columbia.

In Mount Rainier National Park this animal is found irregularly from park boundaries to 6,000 feet. It is not common and is rarely seen.

The usual habitats of the jumping mice are the subalpine parks and meadows, where they may sometimes be abundant in a restricted locality. They hibernate from early fall until late spring, and during their period of summer activity they rarely leave the nest during daylight hours. The nests are on the ground, small and dome-shaped, made of dried grasses.