Don't be surprised if these caribous take flight! Ever since Clement Clarke Moore assigned reindeer to be Santa's helpers in his 1823 poem 'A Visit from St. Nicholas,' caribous—as they are called in North America—have eagerly contributed to the Christmas celebration. It's no wonder that Father Christmas would pick them. Thanks to their resilient and adaptable features, like their two layers of dense fur or eyes adapted to a wide range of light wavelengths, these mammals are accustomed to diverse environments. You likely won't see them fly, but you might find a herd migrating from tundra to forest in the North Polar Region, North America, Northern Europe and Siberia. Their hooves can expand or shrink in size depending on the season and the quality of the ground, which keeps their heavy frame, crowned with antlers, standing on stable feet. If you're celebrating Christmas today, we wish you a merry one.