Caribou (North America)

Reindeer (in North American English, known as caribou if wild and ''reindeer'' if domesticated) are deer in the genus ''Rangifer''. For the last few decades, reindeer were assigned to one species, ''Rangifer tarandus'', with about 10 subspecies. A 2022 revision of the genus elevated five of the subspecies to species (see Taxonomy below). They have a circumpolar distribution and are native to the Arctic, sub-Arctic, tundra, boreal forest, and mountainous regions of northern Europe, Siberia, and North America.

Reindeer occur in both migratory and sedentary populations, and their herd sizes vary greatly in different regions. The tundra subspecies are adapted for extreme cold, and some are adapted for long-distance migration.

Reindeer vary greatly in size and color from the smallest species, the Svalbard reindeer (''R. t. platyrhynchus''), to the largest subspecies, Osborn's caribou (''R. t. osborni''). Although reindeer are quite numerous, some species and subspecies are in decline and considered vulnerable. They are unique among deer (Cervidae) in that females may have antlers, although the prevalence of antlered females varies by species and subspecies.

Reindeer are the only successfully semi-domesticated deer on a large scale in the world, and both wild and domesticated reindeer have been an important source of food, clothing, and shelter for Arctic people throughout history and are still herded and hunted today. Wild reindeer "may well be the species of single greatest importance in the entire anthropological literature on hunting." In some traditional Christmas legends, Santa Claus's reindeer pull a sleigh through the night sky to help Santa Claus deliver gifts to good children on Christmas Eve.

Description

Names follow international convention before the recent revision (see Taxonomy below). Reindeer/caribou (''Rangifer'') vary in size from the smallest species, the Svalbard reindeer (''R. t. platyrhynchus''), to the largest subspecies, Osborn's caribou (''R. t. osborni''). They also vary in coat color and antler architecture.

The North American range of caribou extends from Alaska through the Yukon, the Northwest Territories and Nunavut throughout the tundra, taiga and boreal forest and south through the Canadian Rockies. Of the seven subspecies, the migratory mainland barren-ground caribou of Arctic Alaska and Canada (''R. t. groenlandicus''), summer in tundra and winter in taiga, a transitional forest zone between boreal forest and tundra; the nomadic Peary caribou (''R. t. pearyi'') lives in the polar desert of the High Arctic archipelago; Osborn's caribou (''R. t. osborni'') and three other subspecies are montane. The extinct, insular Queen Charlotte Islands caribou (''R. t. dawsoni''), lived on Graham Island in Haida Gwaii (formerly the Queen Charlotte Islands).

The boreal woodland caribou (''R. t. caribou''), lives in the boreal forest of Labrador and Newfoundland of northeastern Canada: the Labrador or Ungava caribou (''R. t. caboti''), and the Newfoundland caribou (''R. t. terranovae'') have been found to be genetically in the woodland caribou lineage.

In Eurasia, both wild and domesticated reindeer are distributed across the tundra and into the taiga. Eurasian tundra reindeer (''R. t. tarandus'') are close to North American reindeer genetically and visually, but with sufficient differences to warrant division into two species. The unique, insular Svalbard reindeer inhabits the Svalbard archipelago. The Finnish forest reindeer (''R. t. fennicus'') is spottily distributed in the coniferous forest zones from Finland to east of Lake Baikal: the Siberian forest reindeer (''R. t. valentinae'', called ''R. t. buskensis'' by American taxonomists) occupies the Altai and Sayan Mountains.

Male ("bull") and female ("cow") reindeer can grow antlers annually, although the proportion of females that grow antlers varies greatly between populations. Antlers are typically larger on males. Antler architecture varies by species and subspecies and, together with pelage differences, can often be used to distinguish between species and subspecies (see illustrations in Geist, 1991 and Geist, 1998).

Status

About 25,000 mountain reindeer (''R. t. tarandus'') still range the mountains of Norway, notably in Hardangervidda, with smaller numbers in Sweden. Russia manages 19 herds of Siberian tundra reindeer (''R. t. sibiricus'') that total about 940,000.Mizin IA (2018) The current state of the wild reindeer in Russia - general overview of the situation. Barents office of WWF Russia Russian Arctic National Park for World Wildlife Fund, Arkhangelsk, Russia, 8 pp. The Taimyr herd of Siberian tundra reindeer is the largest wild reindeer herd in the world, varying between 400,000 and 1,000,000; it is a metapopulation consisting of several subpopulations — some of which are phenotypically different — with different migration routes and calving areas. Kamchatka reindeer, a forest type (''R. t. phylarchus'') formerly included reindeer west of the Sea of Okhotsk, which, however are indistinguishable genetically from the Jano-Indigirka, East Siberian taiga and Chukotka populations of ''R. t. sibiricus.'' Siberian tundra reindeer herds have been in decline but stable or increasing since 2000.

Insular (island) reindeer, classified as Novaya Zemlya reindeer (''R. t. pearsoni'') occupy several island groups: the Novaya Zemlya archipelago (about 5,000 animals at last count, but most of these are domestic or domestic-wild hybrids), the New Siberia archipelago (about 10,000 to 15,000), and Wrangel Island (200 to 300 feral domesticated reindeer).

What was once the second largest herd is the migratory Labrador caribou (''R. t. caboti'') George River herd in Canada, with former variations between 28,000 and 385,000. As of January 2018, there are fewer than 9,000 animals estimated to be left in the George River herd, as reported by the Canadian Broadcasting Corporation. ''The New York Times'' reported in April 2018 of the disappearance of the only herd of southern mountain woodland caribou in the contiguous United States, with an expert calling it "functionally extinct" after the herd's size dwindled to a mere three animals. After the last individual, a female, was translocated to a wildlife rehabilitation centre in Canada, caribou were considered extirpated from the contiguous United States. The Committee on Status of Endangered Wildlife in Canada (COSEWIC) classified the Southern Mountain and Central Mountain populations as Endangered and the Northern Mountain population, ''R. t. osborni'', as Threatened.

Some species and subspecies are rare and three subspecies have already become extinct: the Queen Charlotte Islands caribou from western Canada, Seton's reindeer from Sakhalin and the East Greenland caribou from eastern Greenland, although some authorities believe that the latter, ''R. t. eogroenlandicus'' Degerbøl, 1957, is a junior synonym of the Peary caribou. Historically, the range of the sedentary boreal woodland caribou covered more than half of Canada and into the northern states of the contiguous United States. Woodland caribou have disappeared from most of their original southern range and were designated as threatened in 2002 by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). Environment Canada reported in 2011 that there were approximately 34,000 boreal woodland caribou in 51 ranges remaining in Canada (Environment Canada, 2011b), although those numbers included montane populations now recognized as subspecies of the Arctic caribou. Siberian tundra reindeer herds are also in decline, and ''Rangifer'' as a whole is considered to be vulnerable by the IUCN.

Naming

Charles Hamilton Smith is credited with the name ''Rangifer'' for the reindeer genus, which Albertus Magnus used in his ''De animalibus'', fol. Liber 22, Cap. 268: "Dicitur Rangyfer quasi ramifer". This word may go back to the Saami word ''raingo''. Carl Linnaeus chose the word ''tarandus'' as the specific epithet, making reference to Ulisse Aldrovandi's ''Quadrupedum omnium bisulcorum historia'' fol. 859–863, Cap. 30: De Tarando (1621). However, Aldrovandi and Conrad Gessner thought that ''rangifer'' and ''tarandus'' were two separate animals. In any case, the ''tarandos'' name goes back to Aristotle and Theophrastus.

The use of the terms ''reindeer'' and ''caribou'' for essentially the same animal can cause confusion, but the International Union for Conservation of Nature clearly delineates the issue: "Reindeer is the European name for the species of ''Rangifer,'' while in North America, ''Rangifer'' species are known as Caribou." The word ''rein'' is of Norse origin. The word ''deer'' was originally broader in meaning but became more specific over time. In Middle English, ''der'' meant a wild animal of any kind, in contrast to ''cattle''. The word ''caribou'' comes through French, from the Mi'kmaq ''qalipu'', meaning "snow shoveler", and refers to its habit of pawing through the snow for food.

Because of its importance to many cultures, ''Rangifer'' and some of its subspecies have names in many languages. Inuvaluit of the western Canadian Arctic and Inuit of the eastern Canadian Arctic, who speak different dialects of Inuktitut, both call the barren-ground caribou ''tuktu''. The Wekʼèezhìi people, a Dene (Athapascan) group, call Arctic caribou ''Ɂekwǫ̀'' and the boreal woodland caribou ''tǫdzı''. The Gwich'in people (also a Dene group) have over 24 distinct caribou-related words.

Reindeer are also called ''tuttu'' by the Greenlandic Inuit and ''rensdyr'' or ''rener'' by the Danes.

Evolution

The "glacial-interglacial cycles of the upper Pleistocene had a major influence on the evolution" of ''Rangifer'' species and other Arctic and subarctic species. Isolation of tundra-adapted species ''Rangifer'' in Last Glacial Maximum refugia during the last glacial – the Wisconsin glaciation in North America and the Weichselian glaciation in Eurasia – shaped "intraspecific genetic variability" particularly between the North American and Eurasian parts of the Arctic.

Reindeer/caribou (''Rangifer'') are in the subfamily Odocoileinae, along with roe deer (''Capreolus''), moose (''Alces''), and Chinese water deer (''Hydropotes''). These antlered cervids split from the horned ruminants ''Bos'' (cattle and yak), ''Ovis'' (sheep) and ''Capra'' (goats) about 36 million years ago. The Eurasian clade of Odocoileinae (Capreolini, Hydropotini and Alcini) split from the New World tribes of Capreolinae (Odocoileini and Rangiferini) in the Late Miocene, 8.7–9.6 million years ago. ''Rangifer'' “evolved as a mountain deer, ...exploiting the subalpine and alpine meadows...”. ''Rangifer'' originated Late Plioicene and diversified in the Early Pleistocene, a 2+ million-year period of multiple glacier advances and retreats. Several named ''Rangifer'' fossils in Eurasia and North America predate the evolution of modern tundra reindeer.

Archaeologists distinguish “modern” tundra reindeer and barren-ground caribou from primitive forms — living and extinct — that did not have adaptations to extreme cold and to long-distance migration. They include a broad, high muzzle to increase the volume of the nasal cavity to warm and moisten the air before it enters the throat and lungs, bez tines set close to the brow tines, distinctive coat patterns, short legs and other adaptations for running long distances, and multiple behaviors suited to tundra, but not to forest (such as synchronized calving and aggregation during rutting and post-calving). As well, many genes, including those for vitamin D metabolism, fat metabolism, retinal development, circadian rhythm, and tolerance to cold temperatures, are found in tundra caribou that are lacking or rudimentary in forest types. For this reason, forest-adapted reindeer and caribou could not survive in tundra or polar deserts. The oldest undoubted ''Rangifer'' fossil is from Omsk, Russia) dated to 2.1-1.8 Ma. The oldest North American ''Rangifer'' fossil is from the Yukon, 1.6 million years before present (BP). A fossil skull fragment from Süßenborn, Germany, ''R. arcticus stadelmanni'', (which is probably misnamed) with “rather thin and cylinder-shaped” antlers, dated to the Middle Pleistocene (Günz) Period, 680,000-620,000 BP. ''Rangifer'' fossils become increasingly frequent in circumpolar deposits beginning with the Riss glaciations, the second youngest of the Pleistocene Epoch, roughly 300,000–130,000 BP. By the 4-Würm period (110,000–70,000 to 12,000–10,000 BP), its European range was extensive, supplying a major food source for prehistoric Europeans. North American fossils outside of Beringia that predate the LGM are of Rancholabrean age (240,000–11,000 years BP) and occur along the fringes of the Rocky Mountain and Laurentide ice sheets as far south as northern Alabama; and in Sangamonian deposits (~100,000 years BP) from western Canada.

A Pearyi-sized caribou occupied Greenland before and after the LGM and persisted in a relict enclave in northeastern Greenland until it went extinct about 1900 (see discussion of ''R. t. eogroenlandicus'' below). Archaeological excavations showed that larger barren-ground-sized caribou appeared in western Greenland about 4,000 years ago.

The late Valerius Geist (1998) dates the Eurasian reindeer radiation dates to the large Riss glaciation (347,000 to 128,000 years ago), based on the Norwegian-Svalbard split 225,000 years ago. Eurasian forest reindeer (''R. t. fennicus'') likely evolved from ''Cervus angifergeuttardi'' Desmarest, 1822, a reindeer that adapted to forest habitats in Eastern Europe as forests expanded during an interglacial period before the LGM (the Würmian or Weichsel glaciation);. The fossil species ''geuttardi'' was later replaced by ''R. constantini'', which was adapted for grasslands, in a second immigration 19,000–20,000 years ago when the LGM turned its forest habitats into tundra, while ''fennicus'' survived in isolation in southwestern Europe. ''R. constantini'' was then replaced by modern tundra/barren-ground caribou adapted to extreme cold, probably in Beringia, before dispersing west (''R. t. tarandus'' in the Scandinavian mountains and ''R. t. sibiricus'' across Siberia) and east (''R. t. groenlandicus'' in the North American Barrenlands) when rising seas isolated them. Likewise in North America, DNA analysis shows that woodland caribou (''R. caribou'') diverged from primitive ancestors of tundra/barren-ground caribou not during the last glacial maximum, 26,000–19,000 years ago, as previously assumed, but in the Middle Pleistocene around 357,000 years ago. At that time, modern tundra caribou had not even evolved. Woodland caribou are likely more related to extinct forest caribou subspecies than to barren-ground caribou. For example, the extinct caribou ''Torontoceros angiferhypogaeus'', had features (robust and short pedicles, smooth antler surface, and high position of second tine) that relate it to forest caribou.

Humans started hunting reindeer in both the Mesolithic and Neolithic Periods, and humans are today the main predator in many areas. Norway and Greenland have unbroken traditions of hunting wild reindeer from the last glacial period until the present day. In the non-forested mountains of central Norway, such as Jotunheimen, it is still possible to find remains of stone-built trapping pits, guiding fences and bow rests, built especially for hunting reindeer. These can, with some certainty, be dated to the Migration Period, although it is not unlikely that they have been in use since the Stone Age.

Cave paintings by ancient Europeans include both tundra and forest types of reindeer.

Taxonomy

Carl Linnaeus in 1758 named the Eurasian tundra species ''Cervus tarandus'', the genus ''Rangifer'' being credited to Smith, 1827.

''Rangifer'' has had a convoluted history because of the similarity in antler architecture (brow tines asymmetrical and often palmate, bez tines, a back tine sometimes branched, and branched at the distal end, often palmate). Because of individual variability, early taxonomists were unable to discern consistent patterns among populations, nor could they, examining collections in Europe, appreciate the difference in habitats and the differing function they imposed on antler architecture. For example, woodland caribou males, rutting in boreal forest where only a few females can be found, collect harems and defend them against other males, for which they have short, straight, strong, much-branched antlers, beams flattened in cross-section, designed for combat—and not too large, so as not to impede them in forested winter ranges. By contrast, modern (see Evolution above) tundra caribou have synchronized calving as a predator-avoidance strategy, which requires large rutting aggregations. Males cannot defend a harem because, while he was busy fighting, they would disappear into the mass of the herd. Males therefore tend individual females; their fights are infrequent and brief. Their antlers are thin, beams round in cross-section, sweep back and then forward with a cluster of branches at the top; these are designed more for visual stimulation of the females. Their bez tines are set low, just above the brow tine, which is vertically flattened to protect the eyes while the buck "threshes" low brush, a courtship display. The low bez tines help the wide flat brow tines dig craters in the hard-packed tundra snow for forage, for which reason brow tines are often called "shovels" in North America and "ice tines" in Europe. The differences in antler architecture reflect fundamental differences in ecology and behavior, and in turn deep divisions in ancestry that were not apparent to the early taxonomists.

Similarly, working on museum collections where skins were often faded and in poor states of preservation, early taxonomists could not readily perceive differences in coat patterns that are consistent within a subspecies, but variable among them. Geist calls these "nuptial" characteristics: sexually selected characters that are highly conserved and diagnostic among subspecies.

Towards the end of the 19th century, national museums began sending out biological exploration expeditions and collections accumulated. Taxonomists, usually working for the museums began naming subspecies more rigorously, based on statistical differences in detailed cranial, dental and skeletal measurements than antlers and pelage, supplemented by better knowledge of differences in ecology and behavior. From 1898 to 1937, mammalogists named 12 new species (other than barren-ground and woodland, which had been named earlier) of caribou in Canada and Alaska, and three new species and nine new subspecies in Eurasia, each properly described according to the evolving rules of zoological nomenclature, with type localities designated and type specimens deposited in museums (see table in Species and subspecies below). Supplementary file 1 for .

In the mid-20th century, as definitions of "species" evolved, mammalogists in Europe and North America made all ''Rangifer'' species conspecific with ''R. tarandus'', and synonymized most of the subspecies. Banfield's often-cited ''A Revision of the Reindeer and Caribou, Genus'' Rangifer (1961), eliminated ''R. t. caboti'' (the Labrador caribou), ''R. t. osborni'' (Osborn's caribou — from British Columbia) and ''R. t. terranovae'' (the Newfoundland caribou) as invalid and included only barren-ground caribou, renamed as ''R. t. groenlandicus'' (formerly ''R. arcticus'') and woodland caribou as ''R. t. caribou''. However, Banfield made multiple errors, eliciting a scathing review by Ian McTaggart-Cowan in 1962. Most authorities continued to consider all or most subspecies valid; some are quite distinct. In his chapter in the authoritative 2005 reference work ''Mammal Species of the World'', referenced by the American Society of Mammalogists, English zoologist Peter Grubb agreed with Valerius Geist, specialist on large mammals, that these subspecies were valid (i.e., before the recent revision): In North America, ''R. t. caboti'', ''R. t. caribou'', ''R. t. dawsoni'', ''R. t. groenlandicus'', ''R. t. osborni'', ''R. t. pearyi'', and ''R. t. terranovae''; and in Eurasia, ''R. t. tarandus'', ''R. t. buskensis'' (called ''R. t. valentinae'' in Europe; see below), ''R. t. phylarchus'', ''R. t. pearsoni'', ''R. t. sibiricus'' and ''R. t. platyrhynchus''. These subspecies were retained in the 2011 replacement work ''Handbook of Mammals of the World vol. 2: Hoofed Mammals''. Most Russian authors also recognized ''R. t. angustirostris'', a forest reindeer east of Lake Baikal''.''

However, since 1991, many genetic studies have revealed deep divergence between modern tundra reindeer and woodland caribou. Geist (2007) and others continued arguing that the woodland caribou was incorrectly classified, noting that "true woodland caribou, the uniformly dark, small-maned type with the frontally emphasized, flat-beamed antlers", which is "scattered thinly along the southern rim of North American caribou distribution" He affirms that the "true woodland caribou is very rare, in very great difficulties and requires the most urgent of attention."

In 2011, noting that the former classifications of ''Rangifer tarandus'', either with prevailing taxonomy on subspecies, designations based on ecotypes, or natural population groupings, failed to capture "the variability of caribou across their range in Canada" needed for effective subspecies conservation and management, COSEWIC developed Designated Unit (DU) attribution, an adaptation of "evolutionary significant units". The 12 designated units for caribou in Canada (that is, excluding Alaska and Greenland), based on ecology, behavior and, importantly, genetics (but excluding morphology and archaeology) essentially followed the previously-named subspecies distributions, without naming them as such, plus some ecotypes. Ecotypes are not phylogenetically based and cannot substitute for taxonomy.

Meanwhile, genetic data continued to accumulate, revealing sufficiently deep divisions to easily separate ''Rangifer'' back into six previously named species and to resurrect several previously named subspecies. Molecular data showed that Greenland caribou (''R. t. groenlandicus'') and Svalbard reindeer (''R. t. platyrhynchus''), although not closely related to each other, were the most genetically divergent among ''Rangifer'' clades; that modern (see Evolution above) Eurasian tundra reindeer (''R. t. tarandus'', ''R. t. sibiricus'') and North American barren-ground caribou (''R. t. groenlandicus''), although sharing ancestry, were separable at the subspecies level; that Eurasian forest reindeer (''R. t. fennicus'') clustered well apart from both wild and domesticated tundra reindeer and that woodland caribou (''R. t. caribou'') were separable from all others. Meanwhile archaeological evidence was accumulating that Eurasian forest reindeer descended from an extinct forest-adapted reindeer and not from tundra reindeer (see Evolution above); since they do not share a direct common ancestor, they cannot be conspecific. Similarly, woodland caribou diverged from the ancestors of Arctic caribou before modern barren-ground caribou had evolved, and were more likely related to extinct North American forest reindeer (see Evolution above). Lacking a direct shared ancestor, barren-ground and woodland caribou cannot be conspecific.

Molecular data also revealed that the four western Canadian montane ecotypes are not woodland caribou: they share a common ancestor with modern barren-ground/tundra reindeer and caribou, but distantly, having diverged > 60,000 years agoYannic G, Pellissier L, Ortego J, Lecomte N, Couturier S, Cuyler C, Dussault C, Hundertmark KJ, Irvine RJ, Jenkins DA, Kolpashikov L, Mager K, Musiani M, Parker KL, Røed KH, Sipko T, Þórisson SG, V.Weckworth B, Guisan A, Bernatchez L, Côté SD (2013) Genetic diversity in caribou linked to past and future climate change. Nature Climate Change 4: 132-137. doi:10.1038/NCLIMATE2074. — before the modern ecotypes had evolved their cold- and darkness-adapted physiologies and mass-migration and aggregation behaviors, as noted above in Evolution. Before Banfield (1961), taxonomists using cranial, dental and skeletal measurements had unequivocally allied these western montane ecotypes with barren-ground caribou, naming them (as in Osgood 1909Osgood WH (1909) Biological investigations in Alaska and Yukon Territory. US Department of Agriculture Biological survey of North American fauna 1: 1-285. Murie, 1935 and Anderson 1946, among others) ''R. a. stonei'', ''R. a. montanus'', ''R. a. fortidens'' and ''R. a. osborni'', respectively, and this phylogeny was confirmed by genetic analysis.

DNA also revealed two unnamed clades that, based on genetic distance, genetic divergence and shared vs. private haplotypes and alleles, together with ecological and behavioral differences, may justify separation at the subspecies level: the Atlantic-Gaspésie caribou (COSEWIC DU11), an eastern montane ecotype, and the Baffin Island caribou. Neither clade has been formally named.

Jenkins et al. (2012) said that " affin Islandcaribou are unique compared to other Barrenground herds, as they do not overwinter in forested habitat, nor do all caribou undertake long seasonal migrations to calving areas." It also shares a mtDNA haplotype with Labrador caribou, in the North American lineage (i.e., woodland caribou). Røed et al. (1991) had noted:

Among Baffin Island caribou the TFL2 allele was the most common allele (p=0.521), while this allele was absent, or present in very low frequencies, in other caribou populations (Table 1), including the Canadian barren-ground caribou from the Beverly herd. A large genetic difference between Baffin Island caribou and the Beverly herd was also indicated by eight alleles found in the Beverly herd which were absent from the Baffin Island samples.

Jenkins et al. (2018) also reported genetic distinctiveness of Baffin Island caribou from all other barren-ground caribou; its genetic signature was not found on the mainland or on other islands; nor were Beverly herd (the nearest mainly barren-ground caribou) alleles present in Baffin Island caribou, evidence of reproductive isolation.

These advances in ''Rangifer'' genetics were brought together with previous morphological-based descriptions, ecology, behavior and archaeology to propose a new revision of the genus.

Species and subspecies

The following are based on a recent revision. Supplementary file 2 for .

Abbreviations: AMNH American Museum of Natural History; BCPM British Columbia Provincial Museum (= RBCM Royal British Columbia Museum), NHMUK British Museum (Natural History) (originally BMNH), DMNH Denver Museum of Natural History, MCZ Museum of Comparative Zoology, MSI Museum of the Smithsonian Institution, NMC National Museum of Canada (originally the CGS Canadian Geological Survey Museum, now CMN Canadian Museum of Nature), NR Naturhistoriska Riksmuseet, RSMNH Royal Swedish Museum of Natural History, USNM, U. S. National Museum, ZMASL Zoological Museum of the Zoological Institute of the Russian Academy of Sciences (formerly the Zoological Museum of the Academy of Sciences), Leningrad

The table above includes, as per the new revision, ''R. c. caboti'' (the Labrador caribou, Eastern Migratory population DU), and ''R. c. terranovae'' (the Newfoundland caribou DU5), which molecular analyses have shown to be of North American (i.e., woodland caribou) lineage; and four mountain ecotypes now known to be of distant Beringia-Eurasia lineage(see Taxonomy above).

The name ''Tarandus rangifer buskensis'' Millais, 1915, the Busk Mountains reindeer, was selected as the senior synonym to ''R. t. valentinae'' Flerov, 1933, in ''Mammalian Species of the World'' but Russian authors do not recognize Millais and Millais' articles in a hunting travelogue, ''The Gun at Home and Abroad,''Millais JG (1915) The Asiatic reindeer and elk. In: Carruthers D, Millais JG, Wallace HF, Kennion LCRL, Barklay FG (Eds) The Gun at Home and Abroad. London & Counties Press Association Ltd., London, U.K., 216-223. seem short of a taxonomic authority.

The name ''groenlandicus'' is fraught with problems. Edwards (1743)illustrated and claimed to have seen a male specimen (“head of perfect horns...”) from Greenland and said that a Captain Craycott had brought a live pair from Greenland to England in 1738. He named it ''Capra groenlandicus'', Greenland reindeer. Linnaeus, in the 12^th edition of Systema naturae, gave ''grœnlandicus'' as a synonym for ''Cervus tarandus.'' Borowski,disagreed (and again changed the spelling), saying ''Cervus grönlandicus'', was morphologically distinct from Eurasian tundra reindeer. Baird placed it under the genus ''Rangifer'' as ''R. grœnlandicus.'' It went back and forth as a full species or subspecies of the barren-ground caribou (''R. arcticus'') or a subspecies of ''R. tarandus'', but always as the Greenland reindeer/caribou. Taxonomists consistently documented morphological differences between Greenland and other caribou/reindeer in cranial measurements, dentition, antler architecture, etc. Then Banfield (1961) in his famously flawed revision, gave the name ''groenlandicus'' to all the barren-ground caribou in North America, Greenland included because ''groenlandicus'' pre-dates Richardson’s ''R. arctus'',. However, because genetic data shows the Greenland caribou to be the most distantly related of any caribou to all the others (genetic distance, FST = 44%, whereas most cervid (deer family) species have a genetic distance of 2% to 5%)--as well as behavoral and morphological differences--a recent revision returned it to species status as ''R. groenlandicus''. Although it has been assumed that the larger caribou that appeared in Greenland 4,000 years ago originated from Baffin Island (itself unique; see Taxonomy above), a reconstruction of LGM glacial retreat and caribou advance (Yannic et al. 2013) shows colonization by NAL lineage caribou more likely. Their PCA and tree diagrams show Greenland caribou clustering outside of the Beringian-Eurasian lineage.

The name ''R. a. granti'' has a very interesting history. Allen (1902) named it as a distinct species, ''R. granti'', from "western end of Alaska Peninsula, opposite Popoff Island" and noting that:

''Rangifer granti'' is a representative of the Barren Ground group of Caribou, which includes ''R. arcticus'' of the Arctic Coast and ''R. granlandicus'' of Greenland. It is not closely related to ''R. stonei'' of the Kenai Peninsula, from which it differs not only in its very much smaller size, but in important cranial characters and in coloration. ... The external and cranial differences between ''R. granti'' and the various forms of the Woodland Caribou are so great in almost every respect that no detailed comparison is necessary. ... According to Mr. Stone, ''Rangifer granti'' inhabits the " barren land of Alaska Peninsula, ranging well up into the mountains in summer, but descending to the lower levels in winter, generally feeding on the low flat lands near the coast and in the foothills... As regards cranial characters no comparison is necessary with ''R. montanus'' or with any of the woodland forms."

Osgood and Murie (1935), agreeing with ''granti''s close relationship with barren-ground caribou, brought it under ''R. arcticus'' as a subspecies, ''R. a. granti''. Anderson (1946) and Banfield (1961), based on statistical analysis of cranial, dental and other characters, agreed. But Banfield (1961) also synonymized Alaska's large ''R. stonei'' with other mountain caribou of British Columbia and the Yukon as invalid subspecies of woodland caribou, then ''R. t. caribou''. This left the small, migratory barren-ground caribou of Alaska and the Yukon, including the Porcupine caribou herd, without a name, which Banfield rectified in his 1974 ''Mammals of Canada'' by extending to them the name "''granti''". The late Valerius Geist (1998), in the only error of his whole illustrious career, re-analyzed Banfield's data with additional specimens found in an unpublished report he cites as "Skal, 1982", was "not able to find diagnostic features that could segregate this form from the western barren ground type." But Skal 1982 had included specimens from the ''eastern'' end of the Alaska Peninsula and the Kenai Peninsula, the range of the larger Stone's caribou! Later, geneticists comparing barren-ground caribou of Alaska with those of mainland Canada found little difference and they all became the former ''R. t. groenlandicus'' (now ''R. a. arcticus''). ''R. a. granti'' was lost in the oblivion of invalid taxonomy until Alaskan researchers sampled some small, pale caribou from the western end of the Alaska Peninsula, their range enclosing the type locality designated by Allen (1902) and found them to be genetically distinct from all other caribou in Alaska. Thus, ''granti'' was rediscovered, its range restricted to that originally described.

Stone's caribou (''R. a. stonei''), a large montane type, was described from the Kenai Peninsula (where, apparently, it was never common except in years of great abundance), the eastern end of the Alaska Peninsula, and mountains throughout southern and eastern Alaska.Allen JA (1901) Description of a new caribou from Kenai Peninsula, Alaska. Bulletin of the American Museum of Natural History XIV: 143-148. It was placed under ''R. arcticus'' as a subspecies, ''R. a. stonei'', and later synonymised as noted above. The same genetic analyses mentioned above for ''R. a. granti'' resulted in resurrecting ''R. a. stonei''.

Seton's reindeer (''R. f. setoni''), endemic to Sakhalin, was described as ''Rangifer tarandus setoni'' by Flerov, 1933, but Banfield (1961) brought it under ''R. t. fennicus'' as a junior synonym. The wild reindeer on the island are apparently extinct, having been replaced by domestic reindeer.

Some of the ''Rangifer'' species and subspecies may be further divided by ecotype depending on several behavioral factors – predominant habitat use (northern, tundra, mountain, forest, boreal forest, forest-dwelling, woodland, woodland (boreal), woodland (migratory) or woodland (mountain), spacing (dispersed or aggregated) and migration patterns (sedentary or migratory). North American examples are the Torngat Mountains caribou DU10, an ecotype of ''R. c. caboti''; a recently discovered, unnamed clade between the Mackenzie River and Great Bear Lake of Beringian-Eurasian lineage, an ecotype of ''R. a. osborni''; the Atlantic-Gaspésie caribou DU11, an eastern montane ecotype of woodland caribou (''R. c. caribou'') DU6; the Baffin Island caribou, an ecotype of the barren-ground caribou (''R. a. arcticus''); and the Dolphin and Union “herd”, another ecotype of ''R. a. arcticus''. The last three of these likely qualify as subspecies, but have not yet been formally described.

Physical characteristics

Naming in this and following sections follows the taxonomy in the authoritative 2011 reference work, Handbook of Mammals vol. 2 Hoofed Mammals.

Antlers

In most cervid species, only males grow antlers; the reindeer is the only cervid species in which females also grow them normally. Androgens play an essential role in the antler formation of cervids. The antlerogenic genes in reindeer have more sensitivity to androgens in comparison with other cervids.

There is considerable variation among subspecies in the size of the antlers (e.g., they are rather small and spindly in the northernmost subspecies), but on average the bull's antlers are the second largest of any extant deer, after those of the male moose. In the largest subspecies, the antlers of large bulls can range up to in width and in beam length. They have the largest antlers relative to body size among living deer species. Antler size measured in number of points reflects the nutritional status of the reindeer and climate variation of its environment. The number of points on male reindeer increases from birth to 5 years of age and remains relatively constant from then on. "In male caribou, antler mass (but not the number of tines) varies in concert with body mass." While antlers of male woodland caribou are typically smaller than those of male barren-ground caribou, they can be over across. They are flattened in cross-section, compact and relatively dense. Geist describes them as frontally emphasized, flat-beamed antlers. Woodland caribou antlers are thicker and broader than those of the barren-ground caribou and their legs and heads are longer. Quebec-Labrador male caribou antlers can be significantly larger and wider than other woodland caribou. Central barren-ground male caribou antlers are perhaps the most diverse in configuration and can grow to be very high and wide. Osborn's caribou antlers are typically the most massive, with the largest circumference measurements.Allen JA (1902) Description of a new caribou from northern British Columbia and remarks on Rangifer montanus. Bulletin of the American Museum of Natural History XVI: 149-158.

The antlers' main beams begin at the brow "extending posterior over the shoulders and bowing so that the tips point forward. The prominent, palmate brow tines extend forward, over the face." The antlers typically have two separate groups of points, lower and upper.

Antlers begin to grow on male reindeer in March or April and on female reindeer in May or June. This process is called antlerogenesis. Antlers grow very quickly every year on the bulls. As the antlers grow, they are covered in thick velvet, filled with blood vessels and spongy in texture. The antler velvet of the barren-ground caribou and the boreal woodland caribou is dark chocolate brown. The velvet that covers growing antlers is a highly vascularised skin. This velvet is dark brown on woodland or barren-ground caribou and slate-grey on Peary caribou and the Dolphin-Union caribou herd. Velvet lumps in March can develop into a rack measuring more than a metre in length by August.

When the antler growth is fully grown and hardened, the velvet is shed or rubbed off. To the Inuit, for whom the caribou is a "culturally important keystone species", the months are named after landmarks in the caribou life cycle. For example, ''amiraijaut'' in the Igloolik region is "when velvet falls off caribou antlers."

Male reindeer use their antlers to compete with other males during the mating season. Butler (1986) showed that the social requirements of caribou females during the rut determines the mating strategies of males and, consequently, the form of male antlers. In describing woodland caribou, which have a harem-defense mating system, SARA wrote, "During the rut, males engage in frequent and furious sparring battles with their antlers. Large males with large antlers do most of the mating." Reindeer continue to migrate until the bulls have spent their back fat. By contrast, barren-ground caribou males tend individual females and their fights are brief and much less intense; consequently, their antlers are long, and thin, round in cross-section and less branched and are designed more for show (or sexual attraction) than fighting.

In late autumn or early winter after the rut, male reindeer lose their antlers, growing a new pair the next summer with a larger rack than the previous year. Female reindeer keep their antlers until they calve. In the Scandinavian and Arctic Circle populations, old bulls' antlers fall off in late December, young bulls' antlers fall off in the early spring, and cows' antlers fall off in the summer.

When male reindeer shed their antlers in early to midwinter, the antlered cows acquire the highest ranks in the feeding hierarchy, gaining access to the best forage areas. These cows are healthier than those without antlers. Calves whose mothers do not have antlers are more prone to disease and have a significantly higher mortality. Cows in good nutritional condition, for example, during a mild winter with good winter range quality, may grow new antlers earlier as antler growth requires high intake.

According to a respected Igloolik elder, Noah Piugaattuk, who was one of the last outpost camp leaders, caribou (''tuktu'') antlers

According to the ''Igloolik Oral History Project'' (IOHP), "Caribou antlers provided the Inuit with a myriad of implements, from snow knives and shovels to drying racks and seal-hunting tools. A complex set of terms describes each part of the antler and relates it to its various uses". Currently, the larger racks of antlers are used by Inuit as materials for carving. Iqaluit-based Jackoposie Oopakak's 1989 carving, entitled ''Nunali'', which means ""place where people live", and which is part of the permanent collection of the National Gallery of Canada, includes a massive set of caribou antlers on which he has intricately carved the miniaturised world of the Inuit where "Arctic birds, caribou, polar bears, seals, and whales are interspersed with human activities of fishing, hunting, cleaning skins, stretching boots, and travelling by dog sled and kayak...from the base of the antlers to the tip of each branch".

Pelt

The color of the fur varies considerably, both between individuals and depending on season and species. Northern populations, which usually are relatively small, are whiter, while southern populations, which typically are relatively large, are darker. This can be seen well in North America, where the northernmost subspecies, the Peary caribou, is the whitest and smallest subspecies of the continent, while the Selkirk Mountains caribou is the darkest and nearly the largest,Reid, F. (2006). ''Mammals of North America.'' Peterson Field Guides. only exceeded in size by Osborn's caribou ("northern mountains" population DU7).

The coat has two layers of fur: a dense woolly undercoat and longer-haired overcoat consisting of hollow, air-filled hairs. Fur is the primary insulation factor that allows reindeer to regulate their core body temperature in relation to their environment, the thermogradient, even if the temperature rises to . In 1913, Dugmore noted how the woodland caribou swim so high out of the water, unlike any other mammal, because their hollow, "air-filled, quill-like hair" acts as a supporting "life jacket".

A darker belly color may be caused by two mutations of MC1R. They appear to be more common in domestic reindeer herds.

Heat exchange

Blood moving into the legs is cooled by blood returning to the body in a countercurrent heat exchange (CCHE), a highly efficient means of minimizing heat loss through the skin's surface. In the CCHE mechanism, in cold weather, blood vessels are closely knotted and intertwined with arteries to the skin and appendages that carry warm blood with veins returning to the body that carry cold blood causing the warm arterial blood to exchange heat with the cold venous blood. In this way, their legs for example are kept cool, maintaining the core body temperature nearly higher with less heat lost to the environment. Heat is thus recycled instead of being dissipated. The "heart does not have to pump blood as rapidly in order to maintain a constant body core temperature and thus, metabolic rate." CCHE is present in animals like reindeer, fox and moose living in extreme conditions of cold or hot weather as a mechanism for retaining the heat in (or out of) the body. These are countercurrent exchange systems with the same fluid, usually blood, in a circuit, used for both directions of flow.

Reindeer have specialized counter-current vascular heat exchange in their nasal passages. Temperature gradient along the nasal mucosa is under physiological control. Incoming cold air is warmed by body heat before entering the lungs and water is condensed from the expired air and captured before the reindeer's breath is exhaled, then used to moisten dry incoming air and possibly be absorbed into the blood through the mucous membranes. Like moose, caribou have specialised noses featuring nasal turbinate bones that dramatically increase the surface area within the nostrils.

Hooves

The reindeer has large feet with crescent-shaped cloven hooves for walking in snow or swamps. According to the Species at Risk Public Registry (SARA), woodland

Reindeer hooves adapt to the season: in the summer, when the tundra is soft and wet, the footpads become sponge-like and provide extra traction. In the winter, the pads shrink and tighten, exposing the rim of the hoof, which cuts into the ice and crusted snow to keep it from slipping. This also enables them to dig down (an activity known as "cratering") through the snow to their favourite food, a lichen'')."In the winter, the fleshy pads on these toes grow longer and form a tough, hornlike rim. Caribou use these large, sharp-edged hooves to dig through the snow and uncover the lichens that sustain them in winter months. Biologists call this activity "cratering" because of the crater-like cavity the caribou's hooves leave in the snow
All About Caribou
– Project Caribou
. Arcticphoto.co.uk. Retrieved on 16 September 2011.

Size

The females (or "cows" as they are often called) usually measure in length and weigh .Caribou at the Alaska Department of Fish & Game
. Adfg.state.ak.us. Retrieved on 16 September 2011. The males (or "bulls" as they are often called) are typically larger (to an extent which varies between the different subspecies), measuring in length and usually weighing . Exceptionally large bulls have weighed as much as . Weight varies drastically between the seasons, with bulls losing as much as 40% of their pre-rut weight.

The shoulder height is usually , and the tail is long.

The reindeer from Svalbard are the smallest of all. They are also relatively short-legged and may have a shoulder height of as little as , thereby following Allen's rule.

Clicking sound

The knees of many species and subspecies of reindeer are adapted to produce a clicking sound as they walk.Banfield AWF (1966) "The caribou", pp. 25–28 in ''The Unbelievable Land''. Smith I.N. (ed.) Ottawa: Queen's Press, cited in The sounds originate in the tendons of the knees and may be audible from several hundred meters away. The frequency of the knee-clicks is one of a range of signals that establish relative positions on a dominance scale among reindeer. "Specifically, loud knee-clicking is discovered to be an honest signal of body size, providing an exceptional example of the potential for non-vocal acoustic communication in mammals." The clicking sound made by reindeer as they walk is caused by small tendons slipping over bone protuberances (sesamoid bones) in their feet. The sound is made when a reindeer is walking or running, occurring when the full weight of the foot is on the ground or just after it is relieved of the weight.

Eyes

A study by researchers from University College London in 2011 revealed that reindeer can see light with wavelengths as short as 320 nm (i.e. in the ultraviolet range), considerably below the human threshold of 400 nm. It is thought that this ability helps them to survive in the Arctic, because many objects that blend into the landscape in light visible to humans, such as urine and fur, produce sharp contrasts in ultraviolet.Reindeer use UV light to survive in the wild
. Ucl.ac.uk (26 May 2011). Retrieved on 16 September 2011. It has been proposed that UV flashes on power lines are responsible for reindeer avoiding power lines because "...in darkness these animals see power lines not as dim, passive structures but, rather, as lines of flickering light stretching across the terrain."

The tapetum lucidum of Arctic reindeer eyes changes in color from gold in summer to blue in winter to improve their vision during times of continuous darkness, and perhaps enable them to better spot predators.

Biology and behaviors

Seasonal body composition

Reindeer have developed adaptations for optimal metabolic efficiency during warm months as well as for during cold months. The body composition of reindeer varies highly with the seasons. Of particular interest is the body composition and diet of breeding and non-breeding females between the seasons. Breeding females have more body mass than non-breeding females between the months of March and September with a difference of around more than non-breeding females. From November to December, non-breeding females have more body mass than breeding females, as non-breeding females are able to focus their energies towards storage during colder months rather than lactation and reproduction. Body masses of both breeding and non-breeding females peaks in September. During the months of March through April, breeding females have more fat mass than the non-breeding females with a difference of almost . After this, however, non-breeding females on average have a higher body fat mass than do breeding females.

The environmental variations play a large part in reindeer nutrition, as winter nutrition is crucial to adult and neonatal survival rates. Lichens are a staple during the winter months as they are a readily available food source, which reduces the reliance on stored body reserves. Lichens are a crucial part of the reindeer diet; however, they are less prevalent in the diet of pregnant reindeer compared to non-pregnant individuals. The amount of lichen in a diet is found more in non-pregnant adult diets than pregnant individuals due to the lack of nutritional value. Although lichens are high in carbohydrates, they are lacking in essential proteins that vascular plants provide. The amount of lichen in a diet decreases in latitude, which results in nutritional stress being higher in areas with low lichen abundance.

Reproduction and life cycle

Reindeer mate in late September to early November, and the gestation period is about 228–234 days. During the mating season, bulls battle for access to cows. Two bulls will lock each other's antlers together and try to push each other away. The most dominant bulls can collect as many as 15–20 cows to mate with. A bull will stop eating during this time and lose much of his body fat reserves.

To calve, "females travel to isolated, relatively predator-free areas such as islands in lakes, peatlands, lake-shores, or tundra." As females select the habitat for the birth of their calves, they are warier than males. Dugmore noted that, in their seasonal migrations, the herd follows a female for that reason. Newborns weigh on average . In May or June, the calves are born. After 45 days, the calves are able to graze and forage, but continue suckling until the following autumn when they become independent from their mothers.

Bulls live four years less than the cows, whose maximum longevity is about 17 years. Cows with a normal body size and who have had sufficient summer nutrition can begin breeding anytime between the ages of 1 to 3 years. When a cow has undergone nutritional stress, it is possible for her to not reproduce for the year. Dominant bulls, those with larger body size and antler racks, inseminate more than one cow a season.

Social structure, migration and range

Some populations of North American caribou, for example many herds in the barren-ground caribou subspecies and some woodland caribou in Ungava and Labrador, migrate the farthest of any terrestrial mammal, traveling up to a year, and covering . Other North American populations, the boreal woodland caribou for example, are largely sedentary. The European populations are known to have shorter migrations. Island herds, such as the insular Novaya Zemlya and Svalbard reindeer, make local movements. Migrating reindeer can be negatively affected by parasite loads. Severely infected individuals are weak and probably have shortened lifespans, but parasite levels vary between populations. Infections create an effect known as culling: infected migrating animals are less likely to complete the migration.

Normally travelling about a day while migrating, the caribou can run at speeds of . Young calves can already outrun an Olympic sprinter when only 1 day old. During the spring migration, smaller herds will group together to form larger herds of 50,000 to 500,000 animals, but during autumn migrations, the groups become smaller and the reindeer begin to mate. During winter, reindeer travel to forested areas to forage under the snow. By spring, groups leave their winter grounds to go to the calving grounds. A reindeer can swim easily and quickly, normally at about but, if necessary, at and migrating herds will not hesitate to swim across a large lake or broad river.

The barren-ground caribou form large herds and undertake lengthy seasonal migrations from winter feeding grounds in taiga to spring calving grounds and summer range in the tundra. The migrations of the Porcupine caribou herd of barren-ground caribou are among the longest of any mammal. Greenland caribou, found in western Greenland, are "mixed migrators" and many individuals do not migrate; those that do migrate < 60 km. Unlike the individual-tending mating system, aggregated rutting, synchronized calving and aggregated post-calving of barren-ground caribou, Greenland caribou have a harem-defense mating system and dispersed calving and they do not aggregate.

Although most wild tundra reindeer migrate between winter taiga habitats and summer range in tundra, some ecotypes or herds are more or less sedentary. Novaya Zemlya reindeer formerly wintered on the mainland and migrated across the ice to the islands for summer, but only a few now migrate. Forest reindeer, ''R. fennicus'', were formerly distributed in most of the coniferous forest zones south of the tree line, including some mountains, but are now spottily distributed within this zone.

As an adaptation to their Arctic environment, they have lost their circadian rhythm.

Ecology

Distribution and habitat

Originally, the reindeer was found in Scandinavia, Eastern Europe, Greenland, Russia, Mongolia and northern China north of the 50th latitude. In North America, it was found in Canada, Alaska, and the northern contiguous United States from Washington to Maine. In the 19th century, it was still present in southern Idaho. Even in historical times, it probably occurred naturally in Ireland, and it is believed to have lived in Scotland until the 12th century, when the last reindeer were hunted in Orkney. During the Late Pleistocene Epoch, reindeer occurred further south, such as in Nevada, Tennessee, and Alabama in North America and as far south as Spain in Europe. Today, wild reindeer have disappeared from these areas, especially from the southern parts, where it vanished almost everywhere. Large populations of wild reindeer are still found in Norway, Finland, Siberia, Greenland, Alaska and Canada.

According to Grubb (2005), ''Rangifer'' is "circumboreal in the tundra and taiga" from "Svalbard, Norway, Finland, Russia, Alaska (USA) and Canada including most Arctic islands, and Greenland, south to northern Mongolia, China (Inner Mongolia), Sakhalin Island, and USA (northern Idaho and Great Lakes region)." Reindeer were introduced to, and are feral in, "Iceland, Kerguelen Islands, South Georgia Island, Pribilof Islands, St. Matthew Island"; a free-ranging semi-domesticated herd is also present in Scotland.

There is strong regional variation in ''Rangifer'' herd size. There are large population differences among individual herds and the size of individual herds has varied greatly since 1970. The largest of all herds (in Taimyr, Russia) has varied between 400,000 and 1,000,000; the second largest herd (at the George River in Canada) has varied between 28,000 and 385,000.

While ''Rangifer'' is a widespread and numerous genus in the northern Holarctic, being present in both tundra and taiga (boreal forest), by 2013, many herds had "unusually low numbers" and their winter ranges in particular were smaller than they used to be. Caribou and reindeer numbers have fluctuated historically, but many herds are in decline across their range. This global decline is linked to climate change for northern migratory herds and industrial disturbance of habitat for non-migratory herds.

Barren-ground caribou are susceptible to the effects of climate change due to a mismatch in the phenological process, between the availability of food during the calving period.

In November 2016, it was reported that more than 81,000 reindeer in Russia had died as a result of climate change. Longer autumns, leading to increased amounts of freezing rain, created a few inches of ice over lichen