... ...

Episode 311: Reindeer Reboot

Listen on Apple Podcasts

A herd of reindeer (image from hilosophyofscienceportal.blogspot.com)

Reindeer and caribou are classified as the same species and genus, Rangifer tarandus, although usually reindeer is used to refer to Eurasian populations and domesticated animals, regardless of their geographic location, and caribou is the name given to the North American animals.

Reindeer are in the sub family Odocoileinae along roe deer, moose and Chinese water deer, which split away from other horned animals like cattle and yak, sheep and goats around 36 million years ago. Investigations into their genomes have revealed how they evolved to thrive in the challenging Northern hemisphere winters, which are long and dark and often freezing cold for months on end. They have several sets of genes that promote vitamin D metabolism, which is extremely important in animals that through short days with little sunlight. They also have increased genes related to retinal development, for better eyesight in low light conditions, olfactory receptors, for locating food under thick layers of snow, and more genes related to immunity and cold triggered pain.

There are 14 separate subspecies of Caribou (7) and Reindeer (7).  The smallest species, Rangifer tarandus (R.t.) platyrhyncus is the smallest reindeer found in Norway. Then, reindeer such as R.t. fennicus are found in Northern Finland and Russia. Other subspecies range across all of Eurasia to the R. t. sibiricus, which is found in Siberia. Of the 7 subspecies of Caribou, the Woodland Caribou (R. t. caribou) can rarely be found in certain portions of the lower 48 United States and are considered endangered. Other species live throughout the northern most reaches of North America with substantial populations throughout Alaska and Canada.

Breeding seasons and chilly winters: the amazing adaptations of Reindeer

The impressive antlers of the male reindeer (image from sdzwildlifeexplorers.org)

In most cervid species, it is only the males that will grow the impressive antlers that are so emblematic of deer species. But in reindeer, both the males and the females can grow antlers, although the males are considerably larger, second only in size to the bull moose. You can distinguish the sexes by the shape of antlers, as males grow several more branching points than females, which generally have a simpler structure. The size of antlers and the number of points, or tips of the antlers, can give some indication of how healthy the individual is, and if it is receiving the right nutrients.

Svalbard reindeer (Rangifer tarandus platyrhynchus) with bloody antlers shedding velvet. (image from sciencephoto.com)

The impressive head pieces begin to grow in March or April in males, and a little later in May and June for female reindeer. The first nubs will begin to appear from the top of the head, gradually growing to curve backwards over the head. By the time the summer months have arrived, the antlers will sprout a soft, velvety fur, which also has a dense network of tiny capillaries and nerves that allow the antlers to grow even more. In the first week of August, after the height of the summer, the reindeers will begin to rub their heads against trees and rocks, trying to strip off the velvet layer from the antlers to expose the tough, sharp bone underneath, ready to be used in the mating season right around the corner. The technical term for this season is the rut when males will lock their antlers together in a fight to get the most eligible ladies. The toughest, largest males with the most impressive set of antlers can bag up to 15 females in a single season!

Two reindeer battling it out for females in rutting season (image from lapland.fi)

Once this season is complete and the males have competed for their lady friends, the antlers will begin shedding again in November and December. Its not just the antlers that go through changes; the soft, light brown summer coat will shed and be replaced with thick white winter fur and the hooves will develop a tougher layer to break through tough sheet ice and reach food underneath. The winter coat consists of a dense, wool-like undercoat with an overcoat of hollow, air-filled hairs that traps body heat. These quill-like hairs on the overcoat can actually act like a life jacket when reindeer need swim, keeping their heads well above water and allowing them to swim  more efficiently.

Unlike males, females will keep their antlers for some time after the mating season, only shedding them once they have had their calves in the Spring. Antlers are likely used in females to determine dominance at feeding grounds. Those females with the largest antlers are the healthiest as antlers require a lot of resources to grow. With better access to food through pregnancies that require a lot of energy to maintain, these reindeer will produce fitter offspring. Research has shown that those calves with antlerless mothers are more prone to disease and have significantly higher mortality than calves that come from mothers with a good set of antlers. This shows just how important antlers are and can display the health and reproductive fitness of reindeer with just a quick look.

Antlers are not just important for the reindeer but are also an important resource for many indigenous cultures in the Northern Hemisphere. The Sami of Sweden and the Inuit of North America both use reindeer antlers and fashion them into tools like knife handles, shovels and small ornaments. Reindeer are also important to these cultures as they provide them with milk, fur, meat and blood, helping these people survive the long winters in such inhospitable conditions.

The indigenous Sami people of Sweden using a reindeer to pull them across the ice (image from archaeoadventures.com)

It is not just the dense fur of the reindeer that keeps them warm in the bitter winters. Reindeer have adapted a mechanism called the counter-current heat exchange. Blood in arteries supplying the legs and feet is warm from the core temperature of the body. These arteries with warm blood are closely intertwined with veins carrying blood from the colder extremities back towards the core, and they warm the cooler blood in these vessels, helping to maintain core temperature in the freezing cold. In a way, heat is being recycled rather than lost to the surrounding air. This also means the heart doesn’t have to pump as hard to maintain a constant body temperature, saving energy the reindeer can spend on other vital activities, like foraging for food in the ice and snow. Reindeer also have this specialised heat exchange in their nostrils, with incoming cold air being warmed by their body heat before it reaches the lungs. The water condensed from the expired air is used to moisten the cold, dry air being breathed in, which can they be absorbed more efficiently through their mucous membranes.

An example of the counter current heat exchange in the human arm. The same system operates in reindeer legs (image from SlideServe.com)

Some populations of North American caribou need to travel enormous distances, as far as 3000 miles per year, to reach different feeding, mating and calving grounds. Some mass migrations have been estimated to be as large as 1,000,000 individuals, clocking at a top speed of 50 mph. The European populations generally only travel much shorter distances.

Not just for Santa: the cultural significance of Reindeer

Although we associate reindeers with Santa Claus’s sleigh in the modern world, they have a long history with humans, going bac to their early ancestors in the Bronze age, with ancient European cave painting representing reindeer alongside humans. Many cultures in the Northern Hemisphere have long relied on them for food, clothing and shelter, such as the indigenous North American people, the Inuit, and the Sámi from Sweden, who are arguably the most well-known and proficient reindeer herders. They have been domesticated at least twice, probably more, and were herded in large numbers alongside nomadic tribes. Their antlers are essential to their survival, but also very important to these cultures, who would use them to create tool handles, knives and ornaments. These animals were so important they were even celebrated in many cultures and considered symbols of creativity, resourcefulness and knowledge. Their long association with winter festivities eventually led to reindeers being pulled into traditional Christmas myths, as pagans converted to Christianity but brought their ancient legends with them to become part of this new religion. The long-held belief that reindeer would bring lost people safely home over the vast winter desolation is likely the reason they became the leaders of Santa’s sleigh in the songs and stories. They have been used for thousands of years as a docile, dependable means of transport, pulling sleds across snow and ice. It should come as no surprise then that they were chosen as the animals that would pull Santa on the most important night of the year, delivering presents across the world.

The traditional dress of a Reindeer herder in Norway (image from thegaurdian.com)

The first historical mention of Santa transitioning from a white horse to reindeer was documented by Mr. William Gilley in the year 1821 from New York who noticed Santa Clause came to his town with reindeer pulling his sleigh. It was not until the year 1823 when Santa’s Reindeer were chronicled by the Troy Sentinel newspaper, where one of the writers (Clement Clarke Moore) hid out to witness Santa Clause’s visit to his home. He wrote up his observations and titled it ‘Twas the Night Before Christmas.

Losing ground: the conservation status of Reindeer

Although most species of reindeer and caribou are considered as least concern on the IUCN redlist, with relatively large and stable populations across most of their range, some species and subspecies are considered to be vulnerable. Some species, like the Queen Charlotte Islands Caribou and East Greenland Caribou went extinct in the early 20th century and of the species still existing today, the Peary caribou and the Boreal Woodland Caribou are both threatened with declining populations.

For any arctic or Northern hemisphere species, there is always the concern of rising global temperatures and how this may affect them. As the Arctic regions warm, vegetation patterns are shifting, and different plant species are gaining dominance. Reindeer and caribou will have to adapt to this, possibly shrinking their available habitat and increasing competition. As some species are migratory, their needs to be consideration of how land use planning could affect this, especially as climate change may cause the herds to utilise different paths. Early thawing of rivers thanks to increasing temperatures also means reindeers can’t reach the calving grounds in time, and there is a risk that heavily pregnant mothers may drown on the journeys as the waterways are flowing faster than the animals expect, going off their thousands of years of instinct.

Poaching is also a serious concern. Although indigenous tribes do hunt reindeer and rely on them for meat and fur, they take only small numbers and practice good sustainability of populations. But more industrial scale poaching has taken place, with raids carried out by the WWF in 2017 revealing the parts of as many as 20,000 animals taken from wintering feeding and calving grounds. This kind of illegal, unmonitored poaching puts these populations and the indigenous cultures that rely on them at huge risk.

Conservation optimism

Despite their many challenges, these charismatic, iconic animals have attracted the attention of the conservation community, largely because protecting them and their migratory pathways will save so much biodiversity in the region. Organisations like WWF Russia have wildlife crime investigators on the ground in regions where poaching is known to be very high and they have provided new equipment like vehicles, radios and cameras to help these hard working officers tackle illegal hunting over such huge ranges. You can see the range of reindeer and caribou conservation ongoing at Reindeer and caribou – WWF Arctic (arcticwwf.org).

Wildsight is a Canadian not for profit organisation working to protect Caribou through securing essential habitat and promoting more sustainable communities since 1987. They have a specialised programme for Mountain Caribou and have developed a recovery plan to improve the massively fragmented habitat they live in to bring back ancient migratory routes. You can check out this project and more at Wildsight – Protecting wildlife, water and wild spaces.

Awesome videos!


Blix, A.S. and Johnsen, H.K. (1983) ‘Aspects of nasal heat exchange in resting reindeer.’ Journal of Physiology

Melnycky, N.A. Weladji, R.B. Holand, O. and Nieminen, M. (2013) ‘Scaling of antler size in reindeer: sexual dimorphism and variability in resource allocation.’ Journal of Mammaology

Moote, I. (1955) ‘The thermal insulation of caribou pelts.’ Textile Research Journal

Smith, B.E. (1998) ‘Antler size and winter mortality of elk: effects of environment, birth year and parasites.’ Journal of Mammalogy

Thing, H. Olesen, C.R. (1986) ‘Antler possession by west Greenland female caribou in relation to population characteristics.’ Rangifer

Weldenegodgaud, M. Kisun, P. Ming, Y. Honkatukia, M. Peippo, J. Reilas, T. and Kantanen, J. (2020) ‘Genome sequence and comparative analysis of reindeer in northern Eurasia.’ Scientific Reports.


December 21, 2022
Scroll to top