Environmentalist Leanne Allison and wildlife biologist Karsten Heuer follow a herd of 120,000 caribou on foot, across 1,500 kilometres of rugged Arctic tundra.Environmentalist Leanne Allison and wildlife biologist Karsten Heuer follow a herd of 120,000 caribou on foot, across 1,500 kilometres of rugged Arctic tundra.Environmentalist Leanne Allison and wildlife biologist Karsten Heuer follow a herd of 120,000 caribou on foot, across 1,500 kilometres of rugged Arctic tundra.