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