This 8-minute video, shot by Chris Siddall in the late summer of 2006 in Vuntut National Park in the northern Yukon Territory, shows the Porcupine Caribou Herd during their mass migration. The Porcupine Caribou herd is one of the largest migratory barren ground caribou herds in North America. Since the first census was conducted in the early 1970s, the herd's population has shifted between 100,000 and 200,000 animals, but biologists don't know what causes the dramatic variations.
