Which is the largest migratory wild reindeer herd in the world?

The reindeer, also known as the caribou in North America, is a species of deer with circumpolar distribution, native to Arctic, subarctic, tundra, boreal, and mountainous regions of northern Europe, Siberia, and North America. This includes both sedentary and migratory populations. This species varies in size and colour from the smallest subspecies, the Svalbard reindeer, to the largest, the boreal woodland caribou.

The Taimyr herd of migrating Siberian tundra reindeer in Russia is the largest wild reindeer herd in the world, varying between 400,000 and 1,000,000. What was once the second-largest herd is the migratory boreal woodland caribou ('R. t. caribou') George River herd in Canada, with former variations between 28,000 and 385,000. Some subspecies are rare and two have already become extinct: the Queen Charlotte Islands caribou of Canada and the East Greenland caribou from East Greenland.