Type.—Obtained on Church Mountain, 6,000 ft., Mt. Baker Range, British Columbia, just north of international boundary, by A. C. Brooks on August 6, 1895; type in Philadelphia Academy of Natural Sciences.
Racial characters.—Similar to intermedius but darker, browner above and deeper gray beneath; skull large and heavy.
Measurements.—A female from Tye, King County, measures: total length 152; length of tail 40; hind foot 19; ear 12. A female from Tomyhoi Lake, Whatcom County, measures: 170; 45; 20; 15.
Distribution.—The Cascade and Olympic mountains, from Tomyhoi Lake (W. W. D.) on the north, to Mt. Adams ([Taylor] and [Shaw], 1929:23) on the south.
Clethrionomys gapperi (Vigors)
Gapper red-backed mouse
Description.—Red-backed mice are heavy-bodied, short-tailed and short-legged mice, similar in general appearance to the meadow mice (Microtus). Unlike the meadow mice, they possess rooted molars, a primitive character. They do not have grooved incisors, like Synaptomys, or the great difference in the depth of the angles of the lower molars that characterizes both Synaptomys and Phenacomys. Externally Clethrionomys may be recognized by the broad red dorsal area from which they obtain their common name. Their sides are grayish or dusky and the undersides buffy white.
The red-backed mice, including more than one species, range over the boreal parts of the Old and New World. In America they are found in most of Alaska, Canada and the northern United States, and extend southward in the Rocky Mountains and along the Pacific Coast. The one species Clethrionomys gapperi ranges across southern Canada from the Atlantic to the Pacific, extending southward in forested areas to New Mexico. They usually live in clearings in the forest. In the Pend Oreille Mountains saturatus was common in damp, mossy talus slides, along with Microtus longicaudus and Phenacomys intermedius. The Clethrionomys outnumbered the two latter species combined by 25 to 1. In nearby forest, red-backed mice were scarce but no other microtines were found. In the Kettle River Mountains a week later, red-backed mice were rare. A single specimen was taken in a damp place in the forest; none was found in talus slides. Near Stevens Pass, King County, in the Cascades, cascadensis was taken in equal numbers in talus slides and under logs in the forest. Near Dewey Lake, Yakima County, in the Cascades, I took them only in an extensive grassy meadow. In the Blue Mountains I found idahoensis in the dense chaparral, far from forests.
Unlike Microtus, red-backed mice do not make runways, although they sometimes follow the runways of other mammals.
[Taylor] (1920B: 92) found red-backed mice breeding on Mount Rainier from early July to the middle of September. One female gave birth to four young in a nest in his duffle bag.