The caribou is a circumpolar animal. In Europe and Asia, the species occurs as wild or semi-domesticated reindeer, but in Canada and Alaska the great herds are all free-ranging caribou.

The two main caribou herds of the North American Arctic are the Porcupine Herd of northern Yukon and Alaska, and the Bluenose Herd east of the Mackenzie River.

Each year the Porcupine Herd - over 100,000 strong - travels 500 miles / 800 km to a coastal plain where thousands of calves are born each June. Feeding on the nutritious shrubs, grasses, and lichens of the tundra, the calves are quite safe from predators while the adults can restore their strength after the long winter.

Although reindeer are probably one of the oldest domesticated animals, the second-largest wild herd of Rangifer tarandus (reindeer or caribou) in the world is the Taimyr herd on the Taimyr Peninsula of Siberia.

While traditional behaviour often determines the migration routes and seasonal ranges used by caribou, their actual routes are often no more predictable than the wind.