Reindeer Revelations: 9 Captivating Caribou Facts

What exactly do you call those big-antlered Arctic deer hauling Santa’s sleigh? Well, reindeer, right? Sure, but also caribou—an indigenous North American name for the very same creature, one of the heraldic beasts of the Far North.

Caribou and reindeer indeed are the very same species within the deer (cervid) family: Rangifer tarandus, a marvelous relict of the Pleistocene ice ages that continues to thrive (or tries to, anyhow) in high-latitude mountain forests and tundra barrens from northern Russia to the top-of-the-world wilds of Greenland. Conventionally, the animal is called a “reindeer” in Eurasia and a “caribou” in North America; or, sometimes, the former term is applied to those caribou that are “broken” by humankind and used as beasts of burden (including for jolly old Saint Nick).

Read on for nine illuminating reindeer facts, covering everything from reindeer migration to caribou habitat and everything in between—including where Arctic sightseers might be able to spot these tough-as-nails, and often spectacularly far-traveling, ungulates!

(1) They Come in Two Main Ecological Forms or Ecotypes

Both Eurasian reindeer and North American caribou can be broadly differentiated into two ecological forms, aka ecotypes: a migratory Arctic/sub-Arctic barren-ground or tundra form, and a more sedentary and southerly forest or woodland form specialized for boreal forest (taiga) and montane habitats.

Tundra caribou mass in large herds and migrate long distances, often between winter range in taiga and summer range on Arctic tundra. Forest caribou occupy much smaller annual ranges, though they may make comparatively short vertical migrations: aka, up and down-slope in mountainous country. Indeed, different populations and subspecies of forest caribou are often further divided into “woodland” and “mountain” forms.

There are exceptions, to be sure, but generally forest caribou are larger (up to twice as big, in some cases) and darker than barren-ground caribou, and have shorter, less ornate, and more massive antlers. The different habitats and seasonal lifeways followed by tundra vs. forest caribou make for interesting behavioral differences. The breeding cycle of tundra caribou is typically set in order to synchronize calving for en masse births out on the barrens in order to overwhelm predators. The mating season (i.e., the rut) plays out amid huge gatherings of tundra herds preparing for fall migration, and bulls go about tending to cows rather than trying to corral and hold harems. The longer, more ornate antlers of tundra bulls show off their reproductive fitness to cows and advertise status to other bulls; direct fights between males are relatively rare and tend to be brief clatterings of antlers that quickly break apart.

By contrast, in forest caribou, which live in small groups, bulls maintain harems of cows and defend these vigorously against other males, which means fights can be longer and more intense. Roughly speaking, the shorter, thicker, simpler antlers of forest bulls are designed for physical combat, while the longer, thinner, more elaborate antlers of tundra bulls are designed for display.

(2) Caribou Are Found From Temperate Regions North Into the Arctic

Caribou occupy a vast circumpolar and circumboreal range in the Northern Hemisphere, within which they’re found in habitats ranging from High Arctic tundra to temperate rainforest (in the wet mountains of North America’s interior Northwest, where the mountain caribou is considered a flagship species). The species currently ranges between about 46 and 81 degrees N latitude.

On the northern end of things, caribou can be found in such polar settings as Canada’s Ellesmere Island, Greenland, and Russia’s Novaya Zemlya archipelago. The Peary caribou of the Canadian Arctic Archipelago is an example of a subspecies that appears to be specially adapted to High Arctic island living. The southernmost caribou today, meanwhile, are forest/mountain forms found in the Columbia and Rocky mountains of northwestern North America and in northern Mongolia. However, in historical times, caribou ranged farther south yet.

Woodland (including “mountain”) caribou, for example, were found across parts of the northern belt of the conterminous United States from Maine to Washington, including portions of the Upper Midwest; mountain caribou of the Selkirk Mountains population still inhabited northern Idaho and northeastern Washington into the second decade of the 21st century, but their recent loss marks (for now) the disappearance of caribou in the Lower 48 states.

And in Europe, some records indicate that wild reindeer were found in the British Isles as recently as 800 years ago. (Since the early 1950s, feral reindeer, brought over from Sweden, have roamed Scotland’s Cairngorm Plateau, which has a borderline sub-Arctic—and therefore pretty caribou-friendly—climate.)

Broadening our temporal view into relatively recent “prehistory,” we find caribou—coming of evolutionary age in the Pleistocene and adapted to cold climates—ranging far down into middle latitudes during the closing stretch of the Pleistocene and the opening chapter of the Holocene (our current geologic era). Reindeer inhabited Central Europe until perhaps 11,000 or so years ago.

While dramatic shifts in climate from Pleistocene days to modern times explain a lot of the caribou’s range contraction, humans also directly or indirectly eliminated the animals from many areas, particularly on the southern frontier of reindeer country. But people have also long introduced caribou into non-native range. They were brought to Iceland centuries ago and persist there as a small feral population, and our collective efforts even took free-ranging reindeer to the Southern Hemisphere: Norwegian whalers released them onto the remote island of South Georgia in the early 1900s—that exotic population was eradicated only in the 2010s—and reindeer still hoof around the sub-Antarctic Kerguelen Islands as well as the more temperate Falklands.

(3) They Are Well-Adapted for Cold & Snow

We’ve already mentioned that modern caribou arose in the Pleistocene, a 2.5-million-year epoch defined by oscillating glacial and interglacial periods with concordant expansions and retractions of continental ice sheets and alpine glaciers. Caribou may originally have been a mountain deer that became specialized for high-elevation tundra habitat, and then were able to dramatically expand as colder, wetter periods of the Pleistocene saw tundrascape take over huge swaths of the Northern Hemisphere.

It’s no surprise, then, that caribou are built for cold and for snow. They have broad muzzles with enlarged nasal cavities to warm and moisten frigid air before it’s taken into the lungs; those snouts are also well-furred, helpful when you nose into snow and munch frozen greenery much of the year. Short ears and tails minimize heat loss, and the pelt comes suited in coarse, flat, hollow guard hairs that trap insulating air against the body. Caribou hooves are deeply cloven and dramatically broad, allowing the animals to float not only over snowpack but also the spongy groundcover of summer taiga and tundra; they develop a hardened rim ahead of winter to boost traction on crusted snow and sea ice.

(4) They Are the Greatest Runners Among the Deer Family, and the Most Gregarious Species

Although caribou happily range into forests, as we’ve seen, their Ice Age-forged bodyplan is that of an open-country runner. They are the most cursorial—that is, running-adapted—of all deer, capable of covering ground quickly and doing so for extended distances. That’s a handy adaptation when you’re exposed to such predators as gray wolves (and humans) in wide-open landscapes. Unlike the young of other species of deer, which generally spend their early days as “hiders,” caribou calves are precocial—active and mobile shortly after being born—and able to run alongside their mothers within a few hours of life: another element of the reindeer’s on-the-go lifestyle.

Their big, paddle-shaped hooves and hollow guard hairs also make caribou excellent swimmers—and, indeed, many herds regularly cross large Arctic rivers and even seawater straits on their migrations.

While forest caribou exist in small groups, tundra caribou mass in herds that can be tremendously large: in the hundreds of thousands. The largest current caribou herd is Russia’s Taimyr herd, which has approached a million head at times. No other deer gathers in such numbers.

(5) They Are the Only Deer in Which Both Males & Females Wear Antlers

In most cervids, only the males—the bucks, stags, and bulls—carry antlers, which are the fastest-growing bones in the animal kingdom, being generated anew each year and then (typically) shed after the breeding season. But both male and female caribou carry antlers. Those of caribou cows may be smaller and spindlier, but they’re antlers nonetheless.

Why do female caribou have antlers? The reason’s likely to do with intraspecific competition. In winter, tundra caribou mainly get their sustenance pawing through snow to access lichen (more on that later), and these “feeding craters” are hot commodities. Cows, which keep their antlers into winter, defend their feeding craters from one another and from bulls—which shed their racks at some point post-rut—using that headgear.

Female woodland caribou don’t always carry antlers, meanwhile—probably because much of that ecotype’s winter diet is arboreal, or tree-dwelling, lichen, which doesn’t require digging feeding craters that must be guarded over.

Bull reindeer antlers are the largest in proportion to their body size of any deer species: They may be 1.4 meters (4.6 feet) long in tundra/barren-ground reindeer. They’re also quite singular among cervids, the curving beams supporting palmate tines—almost as if the racks of an elk (wapiti) or red deer were blended together with those of a moose.

(6) Some Populations Undergo the Greatest Terrestrial Migrations on Earth

As we’ve already mentioned, not all caribou are migratory, and those stocks that are don’t always travel very much over the course of the year. But many Arctic and sub-Arctic herds do indeed cover exceptional distances to execute their annual migrations between taiga wintering grounds and tundra summer range.

A 2019 Scientific Reports study analyzing the long-distance migrations and movements of large mammals showed that caribou indeed perform the lengthiest annual migrations of all, with some herds—such as the Bathurst Herd of central Canada and the Western Arctic herd of Alaska—covering up to 932 miles (1,500 kilometers) each year between winter and summer ranges.

Now, it’s important to note that the study found that caribou, superlatively peripatetic as they are, didn’t actually tread the most ground annually of any large mammal. The researchers found that the gray wolf—the caribou’s numero uno non-human predator—took that crown, with a wolf in Mongolia trotting a mind-boggling 4,503 miles (7,247 km) in a single year. But the wide rangings of wolves and other carnivores—undertaken primarily to locate prey—aren’t (for the most part) migrations, which are defined as annually repeated journeys between distinct seasonal geographies. That said, the study did identify one wolf pack in Canada’s Northwest Territories that appeared to execute an annual migration of sorts in excess of 621 miles (1,000 km)—one driven, it seems, by the migration of caribou the wolves were shadowing. (This is an example of “migration coupling” between wolves and caribou, which appears to be a thing for at least certain wolf packs, while others that target migratory caribou do so when the herds pass through their territories.)

(7) Caribou Vary Widely in Size Across Different Subspecies & Populations

Caribou are among the most morphologically variable deer species. We’ve noted already that woodland caribou tend to be bigger, and sometimes much bigger, than tundra or barren-ground forms. Likely the heftiest caribou in the world, on average, is the Osborn’s caribou of northern British Columbia and southern Yukon, a mountain-caribou type the bulls of which may exceed 700 pounds (318 kilograms). The Selkirk Mountains caribou of interior northwestern North America can approach that size as well.

In harsh High Arctic environments and on both boreal and Arctic islands, reindeer may be much smaller, with a number of “dwarf” subspecies and populations existing in both North America and Eurasia. Compare the hulking Osborn’s caribou, for instance, with the diminutive Svalbard reindeer, the most Lilliputian of caribou: Svalbard bulls max out about 198 pounds (90 kg). Other notably small caribou include the now-extinct Dawson’s caribou of the Haida Gwaii archipelago off Canada’s Pacific coast (killed off in the first half of the 20th century), which stood less than three feet at the shoulder.

(8) They Eat a Variety of Herbivorous Fare, But Lichens Are a Mainstay—Especially in Winter

Caribou are not picky grazers and browsers; they’ll munch on everything from young conifer needles and fresh hardwood shoots to seaweed and mushrooms—including ‘shrooms that are quite toxic to most critters. They’ve even been known to consume animal protein—gobbling up dead lemmings, for example.

All of that said, the caribou diet is most associated with lichens: those symbiotic associations of algae, cyanobacteria, and fungi that are so abundant and diverse in the Arctic and alpine haunts of reindeer. Lichen—including that misnamed species commonly called “reindeer moss”—is an especially critical food for many caribou populations in winter, providing nutritious sustenance that can see herds through the long, cold, dark season in severe high-latitude and high-altitude realms.

This is the prized fodder for which many caribou must doggedly paw through icy snow to reach. In some areas, such as the temperate rainforests of interior northwestern North America, woodland/mountain caribou are able to take advantage of voluminous snowpacks to browse upon arboreal lichens, such as horsehairs, which may also be dislodged to the snow surface when heavy maritime snows break off conifer branches.

(9) They Are the Only Kind of Deer to Have Been Domesticated—and They Have an Ancient Relationship With Humankind

Caribou have been a crucial resource for northern peoples since time immemorial. They appear in Paleolithic and Neolithic cave paintings in Europe; there’s some speculation that the development of the lunar calendar during the Upper Paleolithic was a hunting tool connected to the predictable migration patterns of reindeer. A ford of the Kobuk River along the migration route of the Western Arctic Herd in Alaska has been a hunting hotspot for Native peoples for at least 9,000 years.

In Eurasia, caribou have long been domesticated, a human innovation that happened at least twice independently, goes back millennia, and likely sprang from primordial caribou-hunting seasonal rounds. No other species of deer has been successfully domesticated to any comparable degree. The late, noted ungulate expert Valerius Geist observed that the tameability of caribou calves, especially those of the Eurasian tundra reindeer, likely made this domestication possible. More than three million domesticated reindeer exist in Eurasia, with traditional cultures as diverse as the Sami of Scandinavia and Russia and the Ewenki of northeastern China tending herds.

Where to See Reindeer

From Svalbard—host to those delightfully pintsized endemic reindeer—to the Canadian Arctic Archipelago, not to mention the semi-domesticated herds of Iceland, many of our Arctic cruises take you into the realm of caribou. Explore your options for reindeer-spotting today!