Animals Wildlife 15 Surprising Facts About Reindeer By Melissa Breyer Editorial Director Hunter College F.I.T., State University of New York Cornell University Melissa Breyer is Treehugger’s editorial director. She is a sustainability expert and author whose work has been published by the New York Times and National Geographic, among others. our editorial process Melissa Breyer Updated December 09, 2020 Westend61 / Getty Images Share Twitter Pinterest Email Animals Wildlife Pets Animal Rights Endangered Species Reindeer are known around the world as the fictional sidekicks of Santa Claus, but in polar and mountainous regions, they are very much real and sometimes abundant. Also often called caribou, this species of deer can be found in the Arctic tundra as well as the boreal forests of northern Europe, Canada, and Alaska. Characterized by their long legs, antlers, and crescent-shaped hooves, they exist in two varieties: tundra reindeer, which migrate thousands of miles seasonally in groups of up to half a million, and forest reindeer, which remain in the woodlands year-round. Outside of folk tales and holiday movies, not much is commonly known about the species. While they may not be able to fly in real life, they can, indeed, swim — and see ultraviolet light, among other talents. Discover what makes these majestic creatures so interesting. 1. Reindeer and Caribou Might Not Actually Be the Same Thing Daniel A. Leifheit / Getty Images Although the names are frequently used interchangeably, opinions differ on whether reindeer and caribou are, in fact, one and the same. A genetic mapping published in Nature Climate Change regarding the species Rangifer tarandus (the scientific name for both) shows the migration pattern of these mammals over the last 21,000 years. It claims that reindeer and caribou are different animals — the former inhabiting northern Europe and Asia and the latter North America — albeit closely related cousins. Don Moore, a wildlife biologist for the Smithsonian Conservation Biology Institute, has described reindeer as a “mostly domesticated race of caribou." 2. Their Hooves Change With the Seasons Sandra Leidholdt / Getty Images Because they tend to reside in harsh environments, reindeer undergo a number of physical transformations when the seasons change. During winter, their footpads shrink and tighten, the World Animal Foundation says, exposing the hoof rim so it can cut into ice and snow for traction. In the summer, those pads become sponge-like, ideal for getting around on the soft tundra. 3. Females Have Antlers, Too Andy Price / Getty Images Unique among the more than 45 species of deer, both females and males grow antlers. The males use theirs primarily to battle for females whereas the females use theirs primarily to defend for food. Males' get up to about 50 inches long while females' can reach up to 20 inches, according to the San Diego Zoo. Males shed theirs in late fall or early winter, after the rut, but because females are often pregnant during winter and need to defend their food during pregnancy, they retain theirs until spring. 4. Their Hair Is Hollow RelaxFoto.de / Getty Images The denser the better when it comes to fur coats in the Arctic, one would think. However, while reindeer do have thick, wooly undercoats, their top layer consists of longer, tubular hairs. The hollow shafts allow the hairs to trap air, providing insulation to keep the animals warm in frigid environments. The hollowness of their coats is also what gives them their white color. 5. They Can’t Fly, but They Can Swim Mark Newman / Getty Images That buoyant coat? It's also the reason reindeer are excellent swimmers. They can often be found crossing the vast Yukon River — the third longest in North America, a half mile wide in parts — mid-migration. They swim strongly across these rough and wide rivers and can swim three times faster than the average human at up to 6 mph — which happens to be Michael Phelps's top speed, too. According to the National Park Service, calves just a couple months old have been documented swimming between islands that are a mile and a half apart. 6. Some Travel Far Evgeniia Ozerkina / Getty Images Not all reindeer migrate, but those that do can travel farther than any other terrestrial mammal. According to a study of the longest terrestrial migrations in the world published in Scientific Reports, reindeer and gray wolves were the only species that exceeded 621 miles (1,000 kilometers). With their remarkably long legs, North American reindeer can travel an average of 23 miles per day. 7. They Can See Things Humans Can't burroblando / Getty Images Researchers at University College London discovered that reindeer are the only mammals that can see ultraviolet light. While our inferior human vision allows us to only see wavelengths to around 400 nanometers (each one billionth of a meter), they can see up to 320 nanometers — that includes the spectrum humans can only see with a black light. This helps them spot food and predators more clearly in the blaring light of the Arctic. 8. They Come Out Running Mark Newman / Getty Images The idea of wobbly "Bambi legs" doesn't apply to this type of deer. Within 90 minutes of being born, calves can run as fast as an Olympic sprinter. In a matter of hours, they're able to keep up with the herd. It isn't abnormal for calves to run at speeds of up to 50 mph for 30-some miles a day during migration. That's only slightly slower than the pronghorn (top speed 55 mph), the second-fastest land animal in the world. 9. Babies Are Spotless Patrick J. Endres / Getty Images Also an anomaly for the family Cervidae (the deer family), reindeer calves aren't born with spots. According to Henderson State University, spots on a young deer are an adaptation for survival. Because other deer can't run as fast as adults when they're young, their spots help their mothers locate them if they've been outrun. When running from a predator, the spots break up the pattern of the rushing herd. Because reindeer calves can run as fast as their adult counterparts within hours, they haven't developed the adaptation. 10. They Produce Super Milk Katiekk2 / Getty Images Reindeer milk is said to be some of the richest and most nutritious milk produced by any terrestrial mammal. It contains an impressive 22 percent butterfat and 10 percent protein. For comparison, whole cow milk contains only 3 to 4 percent fat and human milk contains 3 to 5 percent. However, reindeer can only be milked for up to two cups per day. In Nordic countries, the milk of farmed reindeer is made into a kind of sweet cheese. 11. They Live on Lichen Alan Majchrowicz / Getty Images Given the harsh environment, there isn't exactly an abundance of food options for an herbivore. So, the Nordic creatures mostly live on Cladonia rangiferina — aka reindeer moss — which, strangely, also grows in hot environments like Florida. A staple in the reindeer diet, this type of lichen is exceedingly high in carbohydrates and contains a fair amount of vitamins and protein. 12. Male Reindeer Aren't Called Bucks Jérémie LeBlond-Fontaine / Getty Images In yet another departure from the rest of the deer family, reindeer aren't called bucks, does, or fawns. Instead, they share their terminology with cattle: A male is a bull (or in some cases a stag), a female is a cow, and a baby is a calf. It isn't a unique case in the animal kingdom, of course — dolphins are also called bulls and cows. A group of reindeer is called a herd.