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.

Sitting in the northwest corner of Canada, adjacent to the US state of Alaska, Yukon is one of North America's most impressive wilderness destinations. If you have an adventurer's spirit, a love of nature and a passion for exploration, Yukon should be at the top of your holiday destination list. It is not a choice for the feint-hearted, but it is a voyage of discovery with very rich rewards.

If you're looking for a wildlife holiday, where better than one of the wildest places in the world to see caribou, moose, bears, sheep, birds and hundreds of other northern species? Close to 80 percent of the Yukon remains pristine wilderness with just over 10 per cent of the territory fully protected - it has three national parks, six territorial parks and four Canadian Heritage Rivers. Roughly the size of France at 186,661 square miles, the Yukon is home to more than 165,000 caribou, 70,000 moose, 22,000 mountain sheep, 7,000 grizzly bears, 10,000 black bears and 250 species of birds… and only 36,000 humans! In the Yukon, people are outnumbered by caribou by more than 4 to 1!