A hundred thousand caribou face starving bears and wolves, deadly frozen rivers and rugged mountains as they undertake the world's longest land migration - 5,000 kilometres through the frozen Arctic wilderness of Canada and Alaska.
Liz Bonnin leads a team of scientists and film-makers using cutting edge technology to follow the herd, providing insights into the individual lives of the animals. The caribou must reach their calving grounds before they give birth - failure would spell disaster.
