The reindeer (Rangifer tarandus), also known as the caribou in North America, is the only deer species in which both males and females possess antlers. Herds are organized into hierarchies based on the size of the deer's bodies and antlers. Most herds make seasonal migrations, moving to where food is available. Northern populations often travel more than 5000km. During the migration, reindeer groups congregate into great herds of up to half a million individuals.
Reindeer have been domesticated for 3000 years, and there are huge numbers in northern Siberia.