Caribou migration in Noatak National Preserve, Alaska. Some 300,000 caribou reside in the preserve. Every spring and fall, these animals pass through the preserve on the 1,000 km (600 mi) trek between their summer and winter grounds. Noatak National Preserve helps protect this millennia-old journey that is vital to both the caribou and the people who live along their path. Photo courtesy of the US National Park Service.