Caribou

Reindeer is the Eurasian name for Rangifer tarandus; wild North American animals are commonly called caribou. It is a cold-adapted deer with a dense coat, broad hooves, and antlers in both sexes, although their form and timing vary among populations and between males and females. Coat colour and body size also vary widely across the circumpolar range, so measurements from one regional form should not be applied to Mongolia without a population-level source. It is the only living representative of the genus Rangifer. (Wikipedia, general species account)

The species occupies Arctic, subarctic, tundra, boreal, and mountain environments across northern Eurasia and North America. Winter feeding centres on lichens, while willow and birch leaves, sedges, and grasses become important during warmer months. A Mongolian national biodiversity report lists Rangifer tarandus among the country's widely distributed Holarctic mammals, establishing national occurrence but not a precise viewing site. The sources opened for this entry did not provide dependable Mongolia-specific migration timing, herd structure, or locality information, so those details are omitted. (Wikipedia, general species account; Mongolia First National Report to the Convention on Biological Diversity)