It's autumn, and the Porcupine caribou (so named after their calving grounds, namely the Porcupine River, that runs from Canada's Yukon territory to the U.S. state of Alaska) will be starting their annual migration from their wintering grounds in the Alaskan and Yukon boreal forests, over the mountains and to the coastal plain and their calving grounds on the Beaufort Sea coastal plain. The caribou (also known outside North America as reindeer) are seen here crossing Alaska's Kobuk River in Kobuk Valley National Park, both when the river is shallow, as well as when the river becomes deep such that the caribou have to swim through.

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