Reindeer

• 1. The Clicking Deer

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  A walking reindeer clicks, and the sound can be heard from several hundred metres away. The noise comes from small tendons in the legs slipping over bony knobs called sesamoid bones. It happens as the full weight of a foot lands, or just after the weight lifts. Researchers have found that a loud click is an honest signal of body size, so one animal can tell another how big it is without a fight.

  The animal behind the click is the reindeer, Rangifer tarandus, known in North America as the caribou. It lives in a ring around the top of the world, across the Arctic, subarctic, tundra, boreal and mountain regions of Northern Europe, Siberia and North America. It is the only member of its genus. Wild and domestic herds have given Arctic peoples food, clothing and shelter since prehistoric times, and it is the only deer successfully semi-domesticated on a large scale. In some Christmas legends, Santa Claus's reindeer pull a sleigh through the night sky on Christmas Eve.

  Why does one animal carry two names, and who first wrote them down? How does a deer stay warm, fed and sure-footed where few large animals can? Why do females grow antlers when almost every other deer leaves that to males? How many species are there, when scientists have argued over the answer for generations? And why are so many herds shrinking?

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• 2. Names Across Languages

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  The English word reindeer comes from two Old Norse words, hreinn, meaning reindeer, and dýr, meaning animal. It has nothing to do with the reins of a harness. Caribou took a different road. The word reached English through French from the Mi'kmaq word qalipu, which means snow shoveler, a nod to the animal's habit of pawing through snow for food.

  The International Union for Conservation of Nature puts the matter plainly. Reindeer is the European name for Rangifer, and caribou is the North American one. The United States Food and Drug Administration draws its own line in North American English. A wild animal is a caribou, and a domesticated one is a reindeer.

  The scientific name has a tangled paper trail of its own. Charles Hamilton Smith is credited with the genus name Rangifer, in 1827. The medieval writer Albertus Magnus had used the word in his De animalibus, explaining it with the line "Dicitur Rangyfer quasi ramifer". The word may go back to the Sámi word raingo. Carl Linnaeus then chose tarandus as the species name, citing a 1621 book by Ulisse Aldrovandi.

  Aldrovandi and his fellow naturalist Conrad Gessner believed that rangifer and tarandus were two separate animals. The name tarandos itself stretches back to Aristotle and Theophrastus.

  Among the Inuvialuit of the western Canadian Arctic and the Inuit of the eastern Canadian Arctic, the barren-ground caribou is tuktu, even though their dialects differ. The Wekʼèezhìi (Tłı̨chǫ) people, a Dene group, call the Arctic caribou Ɂekwǫ̀ and the boreal woodland caribou tǫdzı. The Gwichʼin, also Dene, have more than 24 distinct caribou-related words. Greenlandic Inuit say tuttu, and Icelanders say hreindýr, sometimes shortened to rein.

  Inuit even name the months after the animal's life cycle. In the Igloolik region, amiraijaut means "when velvet falls off caribou antlers."

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• 3. Built for Cold

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  Fur does most of the work in the reindeer's defense against freezing weather. The coat has a dense woolly undercoat beneath a longer overcoat of hollow, air-filled hairs. It lets the animal regulate its core temperature even when the air climbs to 100 F. In 1913, Dugmore noticed that woodland caribou ride unusually high in the water when swimming. Those quill-like hairs act as a life jacket.

  Colour follows latitude. The northernmost North American subspecies, the Peary caribou, is the whitest and smallest. The Selkirk Mountains caribou is the darkest and nearly the largest, outsized only by Osborn's caribou.

  Blood heading into a reindeer's legs hands its warmth to the cold blood returning toward the body. This arrangement is called countercurrent heat exchange. The legs stay cool while the core stays nearly 30 C warmer, and the heart does not need to pump as fast. Foxes and moose use the same trick.

  The nose runs its own version. Incoming cold air is warmed before it reaches the lungs. Water is condensed out of the breath and captured before the breath leaves the body, then used to moisten the next dry inhalation. As in moose, nasal turbinate bones greatly enlarge the surface inside the nostrils.

  Crescent-shaped cloven hooves carry reindeer across snow and swamp. Woodland caribou have four toes, including two small dew claws. The two big toes bear most of the weight and double as shovels. In summer the footpads turn sponge-like, giving traction on soft wet tundra. In winter they shrink and tighten, exposing a hard rim that bites into ice and crusted snow, and long hair between the toes covers the pads.

  A cow usually measures 162-205 cm in length and weighs 80-120 kg. A bull is typically larger, at 180-214 cm and usually 159-182 kg, though exceptionally large bulls have reached 318 kg. Shoulder height is usually 85-150 cm. The Svalbard reindeer is the smallest, with short legs and a shoulder height as low as 80 cm, which fits Allen's rule about animals in cold climates.

  A 2011 study by researchers at University College London found that reindeer see light as short as 320 nanometres, deep in the ultraviolet. Humans stop at about 400. Urine and fur, which blend into the landscape in visible light, stand out sharply in ultraviolet. The same ability may explain why reindeer shy away from power lines, which in darkness could look like lines of flickering light stretched across the ground. In 2023, researchers in Cairngorms National Park, Scotland, suggested it also helps reindeer pick out UV-absorbing lichens against UV-reflecting snow.

  The reflective layer at the back of an Arctic reindeer's eye, the tapetum lucidum, shifts from gold in summer to blue in winter.

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• 4. Antlers

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  Growth begins in March or April for bulls and in May or June for cows. Reindeer are the only deer in which females normally grow antlers. Their antler-forming genes appear to be more sensitive to androgens than those of other deer. A bull's antlers are the second largest of any living deer, after those of the male moose, and the largest relative to body size. In the biggest subspecies, a large bull's rack can reach 100 cm in width and 135 cm in beam length.

  Antlers are covered while growing in thick velvet, a skin full of blood vessels. The velvet is dark chocolate brown on barren-ground and boreal woodland caribou, and slate-grey on Peary caribou and the Dolphin-Union herd. Velvet lumps seen in March can become a rack more than a metre long by August. The Igloolik elder Noah Piugaattuk described what lies beneath: "The antler is the blood that has hardened."

  The number of points on a male rises from birth until about 5 years of age and then stays roughly constant. Antler mass, though, tracks body mass. Osborn's caribou has the most massive antlers, and central barren-ground bulls grow some of the most varied, very high and wide.

  In the Canadian woodland caribou, rutting males fight in what one government description calls "frequent and furious sparring battles". Two bulls lock antlers and shove. Their thick, flat-beamed antlers suit a harem-defense system, in which large males with large antlers do most of the mating.

  Barren-ground bulls tend individual females instead. Their fights are brief and much less intense. Their antlers are long, thin, round in cross-section and less branched, built more for show than for fighting.

  Shedding follows the rut. In Scandinavian and Arctic Circle populations, old bulls drop their antlers in late December, young bulls in early spring and cows in summer, since females keep theirs until they calve. In midwinter, with the bulls bare, antlered cows rise to the top of the feeding hierarchy and get the best forage. They are healthier for it. Calves of antlerless mothers are more prone to disease and die at a significantly higher rate.

  The Igloolik Oral History Project records that antlers gave the Inuit snow knives, shovels, drying racks and seal-hunting tools. Today large racks serve as carving material. Jackoposie Oopakak's 1989 carving Nunali, in the National Gallery of Canada, covers a massive set of antlers with a miniature world of Arctic birds, caribou, polar bears, seals, whales, fishing, hunting and travel by dog sled and kayak.

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• 5. Lichen and the Long Road

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  Reindeer lichen, Cladonia rangiferina, is the winter staple of the reindeer, and it should be poison. Many lichens make toxic compounds such as usnic acid. The reindeer is the only large mammal able to metabolize lichen, thanks to a rumen bacterium named Eubacterium rangiferina that breaks down usnic acid and may use it as fuel. The animals also carry lichenase, an enzyme that turns lichenin into glucose and that is otherwise found only in some gastropods.

  Lichen is rich in carbohydrates but short on protein, so pregnant reindeer eat less of it. In warmer months the menu widens to willow and birch leaves, sedges and grasses. Reindeer gnaw on shed antlers as a supplement. Under nutritional stress in spring they may eat lemmings, Arctic char or bird eggs, and Chukchi herders have watched their reindeer eagerly devour mushrooms in late summer.

  During the Arctic summer, with daylight around the clock, reindeer sleep in short stretches whenever they need to digest. An EEG study of females in a stable at UiT The Arctic University of Norway showed that the more time a reindeer spends ruminating, the less time it needs in non-rapid eye movement sleep. Ruminating brain waves resemble NREM sleep. That leaves more hours for feeding when food is plentiful.

  The mating season runs from late September to early November. A dominant bull may gather 15-20 cows and stops eating, burning much of his body fat. Gestation lasts about 228-234 days. Cows travel to isolated, relatively predator-free ground such as islands in lakes, peatlands or tundra to calve in May or June. Dugmore noted that migrating herds follow a female for this reason. A newborn weighs about 6 kg, can graze after 45 days and suckles until the following autumn. Cows live up to about 17 years, and bulls about four years fewer.

  Some barren-ground herds and some woodland caribou in Ungava and northern Labrador travel farther than any other land mammal, as much as 5000 km in a year. They cover 19-55 km a day and can run at 60-80 km/h. A calf one day old can already outrun an Olympic sprinter. In spring, small herds merge into groups of 50,000 to 500,000. Swimming at about 6.5 km/h, or 10 km/h if pressed, they cross large lakes and broad rivers without hesitating.

  Parasites trim the migration. Heavily infected animals are weaker and less likely to finish the trip, an effect called culling.

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• 6. Two Million Years

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  The oldest undoubted Rangifer fossil was found at Omsk, Russia, and dates to 2.1-1.8 million years ago. The oldest North American one comes from the Yukon, at 1.6 million years. A 2022 study of ancient DNA from the Kap København Formation in northern Greenland found fragments of Rangifer about 2 million years old. They are among the oldest DNA sequences ever recovered. At that time northern Greenland was 11-19 C warmer than today and held a boreal forest with no modern equivalent.

  The family tree reaches back much further. Antlered deer split from horned animals such as cattle, sheep and goats about 36 million years ago. Rangifer itself began as a mountain deer, grazing subalpine and alpine meadows, and appeared in the Late Pliocene.

  Archaeologists separate modern tundra reindeer from older, primitive forms by features suited to cold and long journeys. These include a broad, high muzzle that warms and moistens air, short legs for running, and behaviours such as synchronized calving. Genes for vitamin D metabolism, fat metabolism, retinal development, circadian rhythm and cold tolerance are found in tundra caribou but lacking or rudimentary in forest types. Forest-adapted animals could not survive in the tundra or the polar desert.

  The modern tundra form probably arose in Beringia. It then spread west into the Scandinavian mountains and across Siberia, and east into the North American Barrenlands, as rising seas isolated the populations.

  Humans began hunting reindeer in the Mesolithic and Neolithic periods. Norway and Greenland have unbroken traditions of hunting wild reindeer from the Last Glacial Period to the present. In the mountains of central Norway, including Jotunheimen, hunters left stone-built trapping pits, guiding fences and bow rests that can be dated with some certainty to the Migration Period. Ancient European cave paintings show both tundra and forest types.

  Excavations show that larger, barren-ground-sized caribou arrived in western Greenland about 4,000 years ago.

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• 7. The Quarrel Over Species

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  For two centuries, naturalists struggled to say where one reindeer population ended and another began. Early taxonomists, working on collections in Europe, saw antlers that looked alike from one animal to the next. They could not see the habitat differences that shaped antler design. Faded and poorly preserved skins also hid the coat patterns that separate subspecies.

  Towards the end of the 19th century, national museums sent out biological expeditions. From 1898 to 1937, mammalogists named 12 new species of caribou in Canada and Alaska, and three new species and nine new subspecies in Eurasia. In the mid-20th century they reversed course, folding all of them into the single species R. tarandus.

  Alexander William Francis Banfield's 1961 revision threw out several subspecies, including the Labrador caribou, Osborn's caribou and the Newfoundland caribou. It drew a scathing review in 1962 from Ian McTaggart-Cowan, who found multiple errors. Most authorities kept using the old subspecies anyway.

  Genetics then forced a rethink. Since 1991, studies have shown deep divergence between modern tundra reindeer and woodland caribou. DNA analysis puts the split around 357,000 years ago, not 26,000-19,000 years ago as long assumed, and at a time before modern tundra caribou existed. Woodland caribou appear closer to extinct North American forest caribou. Eurasian forest reindeer likewise descend from an extinct forest form, not from tundra reindeer. Without a shared direct ancestor, these groups cannot be one species.

  The Greenland caribou shows the scale of the differences. Edwards wrote in 1743 of a live pair brought from Greenland to England in 1738 by a Captain Craycott. Banfield later gave its name to all barren-ground caribou in North America. Yet its genetic distance from the others is 44%, while most deer species differ by 2% to 5%. A recent revision restored it as its own species.

  The small, pale Grant's caribou was described by Allen in 1902, then lost to invalid taxonomy for decades. Alaskan researchers later sampled caribou at the western end of the Alaska Peninsula, within the original type locality, and found them genetically distinct. The subspecies was rediscovered.

  The new revision splits Rangifer into six species. In 2011 Canada's COSEWIC set 12 designatable units for caribou, built on ecology, behaviour and genetics. One distinct group remains unnamed: the Baffin Island caribou, which does not overwinter in forest and shows genetic isolation from the mainland.

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• 8. Shrinking Herds

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  The Taimyr herd of Siberian tundra reindeer is the largest wild herd in the world, and its numbers have swung between 400,000 and 1,000,000. It is a metapopulation of several subgroups with different migration routes and calving areas. Russia manages 19 herds of Siberian tundra reindeer totalling about 940,000. Sweden has approximately 250,000 reindeer in herds run by Sámi villages. About 25,000 mountain reindeer still live in Norway, notably on Hardangervidda.

  The George River herd in Canada was once the second largest, swinging between 28,000 and 385,000. As of January 2018, it had fewer than 9,000 animals left.

  In April 2018, news reports described the disappearance of the only herd of southern mountain woodland caribou in the contiguous United States. An expert called it "functionally extinct" after it dwindled to three animals. The last, a female, was moved to a wildlife rehabilitation center in Canada, and caribou were considered extirpated from the contiguous United States.

  The lost range was once vast. Boreal woodland caribou covered more than half of Canada and reached the northern states from Maine to Washington. In the 19th century reindeer were still present in southern Idaho, and in historical times they probably lived in Ireland. They are believed to have survived in Scotland until the 12th century, when the last were hunted in Orkney. COSEWIC designated the boreal woodland caribou Threatened in 2002. In 2011, Environment and Climate Change Canada reported about 34,000 of them in 51 ranges.

  Three subspecies have already vanished. The East Greenland caribou died out around 1900. The Queen Charlotte Islands caribou of Graham Island in Haida Gwaii disappeared in 1908. The Sakhalin reindeer is thought to have gone extinct around 2007, replaced by domestic reindeer.

  In November 2016, it was reported that more than 81,000 reindeer in Russia had died. Longer autumns brought more freezing rain, which sealed lichen under ice and left the animals to starve. The International Union for Conservation of Nature rates Rangifer as a whole as Vulnerable. The decline is linked to climate change for northern migratory herds and to industrial disturbance for non-migratory ones.

  The zoologist Valerius Geist warned that the true woodland caribou, scattered thinly along the southern rim of the range, "requires the most urgent of attention."

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