"Northern Collared Lemmings live farther north than any other rodent, making their homes on the Arctic tundra. They are among the few North American mammals to turn completely white in winter. Lessening day length triggers other changes as well: they gain weight, sometimes almost doubling their body mass, and develop forked claws for digging through snow and ice. When day length increases in spring, the changes are reversed, and the animal's coat becomes grayish-buff to dark gray. Collared lemmings inhabit high, dry, rocky areas of the tundra. In winter, they may move to meadows at lower elevations."

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Mammal Species of the World