Found in large herds in some of the most northernmost points on Earth, the reindeer - or caribou - is renowned for its ability to withstand the Arctic cold. Although they are built for the cold, reindeer are able to adapt to their climate easily by conserving energy. Reindeer are the only breed of deer where both the male and female grow antlers and are the only mammals that grow new sets of antlers annually. Aside from helping a certain man in red, reindeer are known for their northern migration in the summer, which is one of the largest animal migrations on the planet.