By Dr. Becker
New research suggests that Rudolph the reindeer’s red nose wasn’t his only unique facial feature.
According to a study published in the October issue of the Proceedings of the Royal Society B,1 Rudolph and his Arctic reindeer buddies have eyes that turn blue each year in time for Christmas.
Actually, it’s only a part of the eye that changes color – the tapetum lucidum, also known as the “cat’s eye,” which sits under the unpigmented part of the retina. According to Karl-Arne Stokkan of the University of Tromso in Norway, “In summer, it is golden with most light reflected back directly through the retina, whereas in winter it is deep blue with less light reflected out of the eye.”
The Eyes of Arctic Reindeer Change from a Golden Color in Summer to Blue in Winter
Stokkan studied the reindeer at the University of Tromso. Many of the animals were brought in by mountain region herders and were maintained in large outdoor facilities during the study. Stokkan and his colleagues observed their eyes over two weeks before and after the summer solstice, and another two weeks before and after the winter solstice.
The blue coloring in the reindeers’ eyes during winter provides for increased retinal sensitivity. It may scatter light, making the eyes work harder, which improves sensitivity. According to the researchers, increased sensitivity comes at the expense of sharp vision, but may help reindeer sense predators during dark Arctic winters. And this is an important adaptation, since reindeer are the favored prey of a wide variety of carnivores, including Golden eagles, wolverines, brown bears, polar bears, and gray wolves.
Reindeer, also known as caribou in North America, is a species of deer native to the Arctic and Subarctic. There are both resident and migratory populations.
Reindeer come in many different sizes and colors. Fur color varies considerably, both individually and depending on season and subspecies. Northern populations of reindeer are whiter in color, while southern populations are darker. Reindeer have two-layered coats of fur. There’s a thick woolly undercoat topped by a longer coat made up of hollow hairs.
In most populations, both sexes of reindeer grow antlers, but the antlers of males are typically larger than those of females.
Like the color of their eyes, reindeer hooves also adapt to the season. During summer months when the ground is soft and moist, the footpads become like sponges to provide extra traction. In the winter, the pads shrink and tighten, exposing the rim of the hoof, which is used to cut into the ice and packed snow, also to provide traction. The rims of their hooves also allow reindeer to crater into the snow to reach one of their favorite foods – a lichen known as reindeer moss.