Dec 15, 2024 By Ben Moyer 5 min read

Much of our modern lore surrounding Christmas has roots in nature. Symbolically, at least, we take a tree from the woods and display it in our homes. We hang representations of a parasitic European vining plant above doorways to entice seasonal kisses, and we celebrate Christmas just after the winter solstice, as Earth’s northern hemisphere begins to incline toward the sun and daylength here increases.

Children, especially, delight in another Christmas icon from nature-the reindeer. Here, we’re not accustomed to antlered beasts of burden, but semi-domesticated reindeer herds have provided meat, milk, clothing, tools, and transportation to some cultures in northern Europe and Asia for centuries. Doubtless, Santa’s knowledge of that beneficial relationship prompted him to select reindeer for his sleigh’s propulsion.

But what are reindeer? How are they like, or different from, our familiar deer?

Reindeer is the European name for a deer that lives in sub-arctic regions around the entire northern hemisphere, including northern Europe, Siberia, and North America. Basically, it’s the same species everywhere — Rangifer tarandus-although some ardent taxonomists insist on recognizing regionally varied subspecies. Biologists refer to a species living in all these regions around the northern globe as Holarctic. Other examples of Holarctic animals are the wolf, moose, raven, and polar bear.

In North America, a caribou is the same animal as a reindeer in Europe, but there are no records of Indigenous North American cultures domesticating caribou as people such as the Sami of northern Finland and Norway tamed and herded reindeer.

Reindeer and caribou are both adapted to thrive in extreme cold. The pelt has two layers, a woolly tier next to the skin, and an outer layer of long hollow “guard hairs” filled with air for insulation. People who have seen caribou swimming often comment that they swim “high in the water.” The air-filled outer pelt makes them more buoyant than other mammals. White-tailed deer have hollow, air-filled hairs in their winter coats too, but these have less insulating volume than caribou hair.

Arteries of reindeer and caribou carrying warm blood from the core are closely intertwined with veins bringing cooled blood back from the legs. This intermingling of vessels results in a heat exchange process that makes it easier to maintain a constant internal temperature. Their feet are proportionally larger than those of other deer to support their weight on snow and swampy tundra. In winter, the outer rim of the hooves hardens so the feet can paw through snow and ice to find lichens, the primary winter food. Caribou and reindeer also sometimes gnaw at shed antlers to supplement their nutrition.

Unlike other deer species, female caribou and reindeer typically grow antlers. Biologists are not sure why female reindeer/caribou grow antlers, but the antlers of males (bulls) are much larger.

Wild populations of caribou and reindeer are migratory, and herds travel long distances between summer calving grounds and their wintering habitat in belts of sheltering forest. Caribou herds on Quebec’s Ungava Peninsula undertake the longest migration of any terrestrial mammal, over 3,000 miles. Both caribou and reindeer are preyed upon by wolves and bears. Golden eagles, another Holarctic species, are known to sometimes attack and eat calves. Both are also tormented by mosquitoes and black flies in summer. A caribou can lose up to a quart of blood to insects per week on the tundra.

Our other deer species in North America are the moose, elk, white-tailed deer, and mule deer, sometimes called the black-tailed deer. In Europe, other deer are the moose, and red, roe, and fallow deer.

In some American depictions of Santa’s sleigh, the deer “pulling on the reins” appear to be white-tailed deer. You can tell this by the antlers. But reindeer are the world’s only deer that have been successfully domesticated. Reindeer are still used to pull sleds for transportation and hauling cargo in parts of Siberia. Nomadic herding cultures there prefer deer to dogs for sled-power because reindeer can find their own food on the tundra, while dogs need to be fed meat or fish packed onto the sleigh, adding weight and reducing space for freight. The Russian army used reindeer to move supplies during World War II.

In general, caribou and reindeer populations around the north are not considered endangered, though some local variations are in decline or have gone extinct.

The warming climate does threaten the caribou’s future, both directly and in subtle ways not immediately obvious. As North America’s climate warms, white-tailed deer are able to expand northward into new habitats occupied by caribou. Human alterations of landscape also favor white-tailed deer expansion. White-tailed deer can carry a parasitic brainworm to which they are immune but are lethal to caribou. More interaction between whitetails and caribou can mean more infection.

But those issues are far from the minds of children as Christmas nears and they envision Santa’s reindeer on the roof. The word “reindeer,” by the way, has nothing to do with the reins Santa wields to guide them. Reindeer has its roots in the ancient Norse words “hreinn” and “dyr.”

Merry Christmas. And put out some lichens with the milk and cookies.