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.

Directed by Kiri Cashell.