Wild reindeer swimming across the Kobuk River in Alaska, USA

Reindeer on the move

In autumn, more than 250,000 wild reindeer (known as caribou in North America) come together to form the Western Arctic Caribou Herd and make an epic migration through north-west Alaska, USA. They move south in great numbers, from their calving grounds in the Utukok River Uplands to their winter range on the Seward Peninsula. Scientists attach radio collars to members of the herd, to track their location, health and to learn more about the species. When spring arrives, they’ll complete the trip again in reverse, covering a total of 2,000 miles each year, give or take.

One of the best spots to see the herd on the move is where the great masses of animals cross this river, the Kobuk, at Onion Portage. The name derives from an Inupiaq (Inuit) word meaning wild onions, because so many grow here. But the Inuit people don't just come here for the vegetables. For millennia, the crossing has attracted native peoples who rely on reindeer meat, a tradition that continues to this day.