Most visitors to Denali National Park and Preserve in Alaska come with a checklist for the 'big five' mammals that live here: grizzly bears, moose, wolves, Dall sheep, and caribou like this small group walking along a ridge. These are barren-ground caribou, a migratory subspecies of caribou found across the Arctic band of North America to western Greenland. Barren-ground caribou migrate in large herds, some traveling over 600 miles one way between their summer and winter ranges. But the Denali herd, which numbers around 1,700 animals today, generally stays on the park's 6 million acres. For good reason, too—it's the only large herd that isn't hunted.