Known as reindeer in Europe, but referred to as caribou in North America, these hardy animals can withstand the coldest of winters. In summer, caribou eat willow leaves, sedges, flowering tundra plants, and mushrooms. In winter, they eat lichen and small shrubs. Both male and female caribou grow antlers. They don’t see or hear very well, so they use smell to find food or avoid danger. Caribou live in large herds of up to 500,000. Herds can travel 3,000 miles in a single year, the longest documented movements of any land mammal. Most groups also migrate in the spring and fall, and some herds can move up to thirty-three miles a day. When walking, a tendon in the caribou’s foot slips over a bone, producing a clicking sound. Amplified by thousands, a migrating herd of caribou sounds like a bunch of castanets!