. Distribution of mammals in Colorado. Mammals. 238 MONOGRAPH MUSEUM OF NATURAL HISTORY NO. 3 and (to a lesser extent) M. pennsylvanicus. Microtus montanus is allopatric with the prai- rie vole. Cruzan (1968) studied interactions among the species of Microtus in the Front Range. Typical habitat of the montane vole is moist meadows, but grassy sites well above standing water also are occupied. Runways and burrows frequently are encountered at the bases of aspens (Populus tremuloides). As a generalization, M. montanus has a broader range of ecological tolerance in Colorado than does M. pennsylva
. Distribution of mammals in Colorado. Mammals. 238 MONOGRAPH MUSEUM OF NATURAL HISTORY NO. 3 and (to a lesser extent) M. pennsylvanicus. Microtus montanus is allopatric with the prai- rie vole. Cruzan (1968) studied interactions among the species of Microtus in the Front Range. Typical habitat of the montane vole is moist meadows, but grassy sites well above standing water also are occupied. Runways and burrows frequently are encountered at the bases of aspens (Populus tremuloides). As a generalization, M. montanus has a broader range of ecological tolerance in Colorado than does M. pennsylvanicus, but has narrower limits than M. longicaudus. The altitudinal range of the montane vole is from about 6000 feet in major valleys of the Western Slope to well above timberline. Geographic variation in M. montanus was discussed by Anderson (1954, 1959b); the arrangement of subspecies below generally follows those works. Findley and Jones (1962) provided detailed information on geographic distribution and variation in M. montanus in New Mexico and adjacent Colorado. Microtus montanus fusus Hall Microtus montanus fusus Hall, Proc. Biol. Soc. Washington, 51:133, 23 August 1938; type locality, 2 1/2 mi. E Cochetopa Pass, Saguache Co., Colorado. Distribution in Colorado.—Mountains, high plateaus and mesas of southwestern part of state (Fig. 82). Comparison.—From M. m. nanus, the sub- species geographically adjacent to the north, M. m. fusus differs in slightly paler, more reddish, more yellowish color, slightly nar- rower braincase, and smaller auditory bullae (after Anderson, 1954:494). Measurements.—Mean (and extreme) ex- ternal measurements of seven males from the Grand Mesa are: (145-176), (40- 43), (17-20), (11-18); weight, (). Mean (and extremes) of three males and seven females from the San Juan Mountains and Mesa Verde are: (155- 167), (155-166); (38-47), (38- 47); (20-23), (18-20); (15-17), 14
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