1. Reindeer eyes change colour with the arctic seasons
The eyes of Arctic reindeer change colour through the seasons from gold to blue, adapting to extreme changes of light levels in their environment and helping detect predators.
Researchers funded by BBSRC from UCL (University College London), and the University of Tromsø, Norway, showed that the colour change helps reindeer to see better in the continuous daylight of summer and continuous darkness of Arctic winters, by changing the sensitivity of the retina to light.
The scientists believe this would be an advantage in the prolonged murk of winter, allowing reindeer to more easily detect moving predators, as well as forage. Professor Glen Jeffery from UCL says this the first time a colour change of this kind has been shown in mammals. “This gives them an advantage when it comes to spotting predators, which could save their lives.”
2. Like cats, reindeer eyes glow in the dark
Cats’ eyes aren’t just for cats. Arctic reindeer also have the layer of tissue in the eye called the tapetum lucidum (TL) which lies behind the retina and reflects light back through it to enhance night vision.
In the bright light of summer the TL in Arctic reindeer is gold, similar to many other mammals, which reflects most light back directly through the retina. However by winter it has changed to a deep blue, and this change scatters more light through photoreceptors at the back of the eye, increasing the sensitivity of the retina in response to the limited winter light.
Scientists think the colour change may be caused by pressure within the eyes. In winter, higher eye pressure probably caused by permanent pupil dilation to let light in prevents fluid in the eyeball from draining naturally. This compresses the TL, reducing the space between collagen in the tissue and thus reflecting the shorter wavelengths of the blue light common in Arctic winters.
3. Reindeer are still an essential part of life for the Sami indigenous people (and others)
Reindeer are the only domesticated deer species, providing everything from meat and milk to hides, antlers, and transport. When and where this first occurred is still a matter of debate, because most (ancient) languages didn’t always have a written form. It’s likely that different cultures tamed reindeer independently at different times, and some of the earliest written references to reindeer herding from the early centuries A.D. come from China, but this might reflect where the best records were kept.
The Sami people live in the northern regions of Norway, Sweden, Finland and Russia, and they have approximately 400 words for the food, tools and other products and parts taken from reindeer. Other tribes and people have domesticated (or semi-domesticated) reindeer in areas of Mongolia, China, Greenland, Canada and the US (in Alaska).
4. And they love a bit of reindeer racing
5. Reindeer can see ultraviolet light
Human can see light from red (wavelength around 700nm) through all the colours of the rainbow to violet (at 400nm). In research funded by BBSRC, scientists tested reindeer and found they can see wavelengths down to around 350–320nm, which is termed ultraviolet, or UV. This was the first finding of UV vision in mammals.
Lead researcher Professor Glen Jeffery from UCL says humans and almost all other mammals could never do this because our lenses just don’t let UV through into the eye. “When we used cameras that could pick up UV, we noticed that there are some very important things that absorb UV light and therefore appear black, contrasting strongly with the snow. This includes urine — a sign of predators or competitors; lichens — a major food source in winter; and fur, making predators such as wolves very easy to see despite being camouflaged to other animals that can’t see UV.”
This work led Prof Jeffery to find that ultraviolet sensitivity is probably widespread among mammals.
6. And so reindeer can see electricity discharges from pylons
Reindeer may avoid territory near high voltage power cables because of flashing UV light. Although we humans can’t see it, the video above shows that with a special UV camera, electrical discharges called corona occur when charge builds up in a cable and is released into the air.
It had been recognised for some time that some mammal and bird populations avoided high voltage power lines. But this puzzled scientists because suspended cables were neither a barrier to wildlife, nor are regularly associated with humans as they are often in isolated areas. Reindeers’ avoidance of the power lines (up to 5km each side) running across the Arctic tundra was part of the inspiration for this project.
Researchers think that the bring corona lights startle the animals, which has implications for welfare, migration and conservation in a number of species.
7. Researchers say reindeer and caribou are the same species
Reindeer and caribou are two common names for the same species — Rangifer tarandus — and the latter name is more prevalent in North America. But this species is divided up into 9–13 sub-species, the number of which varies depending on which taxonomist you talk to, and genetic analysis is continuing to reveal secrets of their evolutionary past (and where some threatened groups could be heading).
What differentiates reindeer from other deer species is that the males and females grow antlers — and the females keep theirs or shed them in the spring), whereas the males shed them at the end of the mating season in early December.
8. Which means Santa’s reindeer must all be girls
The sleigh-pulling reindeer are always depicted with antlers, but the males don’t have them at this time.
9. And small Norwegians
Santa’s reindeer are most likely to be the Rangifer tarandus platyrhynchus subspecies, which are found off the north coast of Norway on the Svalbard islands.
This is because the 1823 poem ‘A Visit from Saint Nicholas’ by Clement Moore first introduced the world to Santa’s reindeer, which details “ a miniature sleigh, and eight tiny reindeer”. The Svalbard subspecies fit the bill as they weigh about half as much as other reindeer species and are thus much shorter in length.
They’re smaller because they have likely followed the ‘dwarfing’ tendency often seen in animals on small islands. The tendency is for large animals to become smaller, driven in part by the fact that there isn’t so much food around. The proper term is insular dwarfism (and also applies to small animals that tend to get bigger in the absence of predators) and has been seen in elephants, snakes a dinosaur and perhaps humans.
10. Satellite monitoring has confirmed reindeer can travel further than any other migrating terrestrial mammal
A few populations of North American reindeer travel over 3,100 miles per year (or 2000–6000km) covering around 23 miles per day. This they do between the calving grounds in the tundra and the warmer boreal forest to the south. While not all reindeer migrate, some woodland species living relatively sedentary lifestyles, this makes them the top terrestrial mammal migrators.
Scientists in Quebec, Canada, have used high-performance telemetric collars and satellite data to follow reindeer in migration herds that in spring can range from 50,000 — 500,000 individuals. The technology make it possible to monitor and study many aspects of reindeer biology and behaviour, such as their use of space and survival rates, which can be used to determine conservation measures in the regions where these fascinating and beautiful animals roam.
