Anyone who has travelled across Canada's northern tundra may have glimpsed a herd of caribou moving in single file over the snow. Three main types of caribou range across the country, from the barren grounds of Nunavut to the boreal forests of Ontario and the mountains of British Columbia. For thousands of years the animal has sustained northern peoples with food, clothing, and tools. Today the caribou is honoured as a national emblem and appears on the twenty-five-cent coin, the quarter. Yet behind this familiar figure lies an animal whose whole body is fitted for survival in one of the harshest climates on earth.

Few land mammals are so thoroughly equipped for winter. A caribou's broad, crescent-shaped hooves spread wide to carry it over deep snow and soft muskeg like a pair of snowshoes, and they harden at the rim in the cold to cut into ice. Its coat is made of hollow hairs that trap air and keep the animal warm even at forty below, and those same hollow hairs make it unusually buoyant, so it can swim across wide rivers with ease. Unlike most deer, both the males and the females grow antlers, which the animal sheds and regrows each year.