Gray Red-backed Vole

The gray red-backed vole, also called the gray-sided vole, is a sturdy arvicoline rodent weighing about 20–50g. Its most useful pattern is the contrast between a reddish-brown back and grayer sides, although coat tones vary across its immense northern range. It is larger and longer-legged than the northern red-backed vole, which may occur in the same region. Because small voles are difficult to separate safely in the field, observers should treat colour alone as suggestive rather than conclusive. (Wikipedia, grey red-backed vole account)

This vole feeds on grasses, small herbs, berries, and the leaves and shoots of low shrubs. In tundra populations its abundance can rise sharply on a four- to five-year cycle, creating conspicuous outbreaks before numbers fall again. The broader account places it across northern Eurasia in cool rocky, shrubby, and wooded settings. The Mammal Diversity Database confirms the species for Mongolia, but the sources opened here do not identify a Mongolian locality or describe a country-specific season, so this account avoids a more precise viewing recommendation. (Wikipedia, grey red-backed vole account; Mammal Diversity Database, Mongolia country list)