Through the Eyes of a Reindeer

A visitor recently asked me why reindeer have horizontal pupils. The question had me thinking about the importance of vision to reindeer. It is easy to forget that many animals don’t see the world the same way we do, and reindeer eyes are in many ways different from our own.

Reindeer live in arctic and sub arctic regions that experience hugely variable light levels. Above the arctic circle, they’ll experience 24 hour darkness in winter and 24 hour sun in summer, and no matter how dark it is, they still need to be able to find their food and see predators coming. So how do reindeer eyes cope with their environment?

Origami – Photo by Kate Brown

When you look at a reindeer, the most obvious thing about their eyes is that they are placed on the side of their heads. This is common in prey animals, and it gives them a wide field of vision that means they can see danger coming from almost any direction. The placement of their eyes does mean they have a blind spot right in front of their noses, but aside from this it’s very hard to sneak up on a reindeer!

Ladybird – Photo by Kate Brown

If you look a bit closer, the next thing you might notice – aside from their beautiful eyelashes – is that they have long,  horizontal pupils. This adaption helps focus a reindeer’s sense of sight at the ground level and the horizon – where their food and their predator’s are found. These horizontal pupils also help compensate for the placement of their eyes and reduce the size of that blind spot in front of a reindeer, so that they can see forwards – vital for finding an escape route when on the run from a predator.

Dr. Seuss – Photo by Kate Brown

If you looked deeper into a reindeer’s eyes, you would find even more amazing adaptions. In 2013 scientists discovered that reindeer eyes actually change colour with the seasons! A layer of tissue in the retina changes from a golden colour in summer to a deep blue in winter. This change means that less light is reflected back out of the eye, helping reindeer keep their vision sharp even in the long dark winter months. This is the first time this kind of colour change in a mammalian eye has been found. It is thought the colour change might be caused by increased pressure in the eye in winter. The pupil is permanently dilated in the dark, and this reduces the space in the collagen structure of the retina, which in turn changes the reflectiveness of the retina and shortens the wavelengths of light being reflected.

Two dissected reindeer eyes, the left taken from a reindeer that died in winter, the right from one that died in summer. Photo by Glen Jeffrey (The Independent).

Reindeer vision is made even more interesting by the fact that they can see into the UV range. There are high levels of UV light present in the polar regions of the world due to the reflections from snow and ice. Many lichens – the favoured winter food of reindeer – are very effective at absorbing UV. Wolf fur as well is also shown to absorb UV, so being able to see UV wavelengths helps reindeer pick out both their food and their predators in the snow (see here for a previous blog on UV vision).

Reindeer seem to view the world quite differently to us, and it’s clear their eyes have had to adapt to many challenges. They’ve had to adapt to pick out predators and hard to find food, to cope with extreme seasonal changes in light, and to deal with the large amount of UV present in the arctic. Their eyes are just another example of how well adapted reindeer are for their environments.

Kate

Sources:

Why do animal eyes have pupils of different shapes? | Science Advances (sciencemag.org)

Arctic reindeer extend their visual range into the ultraviolet | Journal of Experimental Biology | The Company of Biologists

Shifting mirrors: adaptive changes in retinal reflections to winter darkness in Arctic reindeer | Proceedings of the Royal Society B: Biological Sciences (royalsocietypublishing.org)

Reach for the sky! How reindeer antlers grow so fast

They’re the most distinctive feature of the reindeer, and the most incredible. Branching elegantly like the trees which the tundra so sorely misses, and renewing themselves each year, antlers demonstrate nature’s complexity and mystery in one. At this time of year the reindeer’s quickly growing antlers constantly amaze visitors and captivate my own imagination. It occurred to me recently that the cells in growing antlers and the cells used in the Covid-19 vaccine are both the same type of rare cell: undifferentiated stem cells! It might be interesting to join the dots between this.

A line of hungry boys and growing antlers (August 2021)
Nell being inspired to write this blog, surrounded by lots of wonderful antlers (July 2021)

Greater Antlers, Greater Chances…

Large antlers lead to a (sexually selective) advantage in males, and even in females too as those that are better able to defend areas of food in the winter are more likely to produce healthy offspring. A physical advantage in a single characteristic, leading to it’s selection is a process called directional selection. This means that over time, reindeer populations evolve very (VERY) gradually to have larger antlers.

Swedish-born (and the very handsome) Kota, who was used as a breeding bull for several years (August 2017)
The lovely Fly, who tends to grow big antlers for a female (September 2019)

However, large antlers come at a cost, requiring huge amounts of energy to grow in such a short space of time. Reindeer eat lichen, which is fairly low in nutrition and has a long digestive process, as well as other low lying plants, mosses and mushrooms found across sub-arctic areas. As even eating a lot of food won’t make up the energy, the animals shift calcium from parts of the skeleton which don’t carry a lot of weight (such as the ribs) in a process called cyclical reversible osteoporosis, which humans also go through during pregnancy. There are still more adjustments, as the reindeer’s neck and shoulder muscles need to swell in order to carry the bulky weight of the antlers, and movement becomes restrictive. It’s no wonder then that the rutting season becomes so taxing for large bulls that their life is typically shorter than that of a female. Taken to an extreme there is even a theory that the great Irish Elk, or Megalocerous, was partially driven to extinction due to the amount of energy it lost to it’s enormous antlers! I find it unlikely that this will happen to the reindeer but there’s no doubt that these huge organs take a lot for the reindeer to grow.

The Irish Elk or Megaloceros with it’s weighty antlers (image: Biggest. Antlers. Ever. Meet the Irish Elk | At the Smithsonian | Smithsonian Magazine)

Shooting for the Skies

Although we know what pushes antlers to grow to such a huge size, it’s truly incredible when we begin to ask how. Antlers are the fastest growing organs in the animal kingdom, potentially growing around three inches a week (dependent on nutrition). This is mainly due to the quick regeneration of stem cells from which they are formed; the only type of cell in a body which can differentiate into any kind of tissue, such as bone, fat or skin. We have some of these cells in our bone marrow, as an important part of our bodily regeneration, and the quick formation of embryos is also due to them. Stem cells are also an important resource in therapies for degenerative diseases or to support the body following certain aggressive cancer treatments. Stem cells have even been used in the creation of several vaccines – including for Covid-19! This, combined with their versatility and potential in lab experiments makes stem cells an extremely valuable resource to medical research. It’s awesome to think that the same cells from which reindeer antlers are formed are what we use to treat life threatening diseases.

Finally, the antlers are not just useful to the reindeer, but also to the other animals in the wider ecosystem. Often when we find an antler which has been out on the hill for a while it will be worn thin and marked by the tooth marks of different animals. In the Paddocks we also see that mice and squirrels chew the antlers in the display area! This is because once they are dropped they are an open source of calcium which sometimes the reindeer, or other animals, (like your own pet dogs) will chew in order to reclaim the minerals. There have even been times that reindeer have chewed each other’s antlers while they’re still on their head!

Reindeer chewing on a cast antler in the enclosure, video by herder Olly

Next spring I plan to photograph the same reindeer once a week from the time it’s antlers are small stumps until they’re fully grown as there really is an incredible difference. There’s so much which is unique and wonderful to say about antlers and I’m looking forward to writing still more about them!

Ryvita (and her lovely antlers) with Nell on the free-range (August 2021)

P.S. What’s the difference between an antler and a horn?…… A horn makes a noise!

Nell

Reindeer calving: Can we predict whether there will be more males or females born?

It has been an exceptionally mild winter here in the Cairngorms; the ski season never really seemed to kick off, the herders are missing the snow and it has just felt a bit wetter and warmer than usual. I’m sure you’ve noticed how early the snowdrops and daffodils seem to have emerged and we have noticed that the hills are looking a bit greener with the heather and deer sedge starting to grow already. Looking at the Met Office summary for winter 2016-2017, temperatures are up about 3.0°C on average (average being data from 1981-2010) in the UK.

OLYMPUS DIGITAL CAMERA
This blog is really just an excuse to look at cute calves. Here’s a reindeer and a red deer calf, both being hand reared.

For the reindeer, this warming winter could have lots of effects, and we have recently heard of the reindeer in the Yamal peninsula, Siberia, starving to death due to increased rainfall in the autumn freezing and leaving a thick layer of ice impenetrable to them for foraging.

Our reindeer seem to be coping just fine and it has not frozen here enough for them not to reach their favourite food, lichen. However, research done by previous reindeer herder Heather Hanshaw has shown that weather conditions do definitely affect the proportion of male to female calves born in the spring. Since calving will soon be upon us, I thought it might interest you to know about this research and what our mild winter may mean for us in the upcoming weeks.

calf
Newborn calf

Heather studied Physical Geography at Edinburgh University and in her final year needed a project to study. Of course, having an interest in climate as well as reindeer, and having worked at the Reindeer Centre, a project about how climate affects them was a natural interest to Heather. She knew that Mr Utsi and Dr Lindgren had been very meticulous about the data kept on calves born in the Cairngorm herd, and climate data was easily enough accessed, so Heather devised a project determining if weather (temperature and rainfall) had any effect on the proportion of male to female reindeer calves born. A similar study was conducted with Red deer on the Isle of Rum, and their study found that milder winters led to more male calves. Would it be the same or opposite of Rum, or would weather have no effect on the Reindeer?

fergus-5
The famous Fergus, asleep on Mel’s rug

It turns out that Reindeer are similar to Red deer and when the winter temperature increases, so does the proportion of male calves. So, will that turn out to be true this year? With only a few weeks until calving begins, it will be interesting to look at whether we have lots of male calves this year.

Last year the winter seemed fairly average, possibly on the warm side a little, and our calving ratio was almost perfectly 1 male to 1 female, so it will be really interesting to see if this mild winter has had an effect on what will be born this May.

Hopscotch and calf
Hopscotch and calf

Please find sources below.

http://www.metoffice.gov.uk/climate/uk/summaries/2017/winter

https://www.newscientist.com/article/2112958-80000-reindeer-have-starved-to-death-as-arctic-sea-ice-retreats/

http://www.nature.com/nature/journal/v399/n6735/abs/399459a0.html

Imogen

 

 

Book Now