Caribou, or Reindeer, is the only deer species in which both males and females have candelabra-like antlers. They live in large, migratory herds along the tree line of northern forests, eating mostly grass-like plants and shrubs in summer, and lichen, which carpets the snow-covered forests, in the winter. Getting at winter feed by digging through the snow can lead to intense competition, which may explain why females also carry antlers. During the breeding season, males compete with one another for access to females, using their antlers in jousting matches. They become completely devoted to the rituals of mating, failing even to eat, and losing their built up energy reserves in the process. Females give birth at traditional calving grounds on the open tundra during the spring, after a gestation of seven months. Then they pour all of their energy reserves into nursing their calves for a month. There are more than 2,000,000 Caribou in North America, but they are less successful in the southern parts of their range where they must cope with humans and other predators.

Links:
Mammal Species of the World
  More images, video and sound of the Peary caribou, a subspecies