‘Tis the season for magical reindeer, and scientists from the University of Norway appear to have found a sort of magic in the eyes of these Arctic creatures. The study has revealed that the eyes of Arctic reindeer change color throughout the year in an effort to cope with the extreme variations in light conditions above the Arctic Circle.
Each year the Arctic Circle experiences a period of approximately 10 weeks when the sun never fully sets, and another period of approximately 10 weeks when the sun never fully rises. These extreme light conditions led researchers to ask the question, how can Arctic reindeer adapt?
The research was conducted with the help of local indigenous herders, known as Sami, who typically harvest Arctic reindeer twice a year, once during the period of near constant light, around the spring solstice, and once during the period of near constant darkness, around the winter solstice. The Sami collected the eyes of the harvested animals and provided them to researchers. What they saw revealed a kind of magic in the reindeer’s eyes.
Glen Jeffrey, one of the researchers on the project said of his initial observation of the interior of the eyes “I had the biggest shock I’ve ever had in science.” He explained that the eyes harvested in the summer appeared gold, while the eyes harvested in the winter appeared blue. The difference could not have been more clear. This discovery marks the first finding of this kind among mammals.
It is explained by a change in color of a reflective layer of tissue known as the tapetum lucidum that exists behind the retina in Arctic Reindeer and many nocturnal animals but does not exist in humans. It is the structure responsible for the glowing glare from an animal’s eyes often referred to as a “deer caught in headlights” look.
When the tapetum lucidum is blue, less light is reflected out of the eye than when it is gold, vision is less clear when they eyes are blue but they are far more sensitive to light. This allows for better vision and in turn better odds of survival in the perpetual near-darkness so that predators and food sources can be more easily located. Jeffery said of the phenomena that “clinically the reindeer becomes glaucomic” during the time that its eyes are blue.
Some say that the findings don’t come as all that much of a shock as many Arctic animals, including Arctic reindeer, undergo many physical changes throughout the year as they try to adapt to extreme variations in living conditions. For Arctic reindeer these other changes can include the addition of a significant amount of body fat, fuller coats and even a coat color change from brown to white thought to help protect them from being easily spotted by predators in the wild.
The changes in eye color among Arctic Reindeer are not limited only to blue and gold either, it would appear. The scientists also studied reindeer living at the University of Tromso, also known as the Arctic University of Norway, and discovered that those reindeer had eyes that turned green in the winter months. They accounted for this variation by explaining that the Arctic University reindeer are perpetually exposed to additional light during the dark winter months from surrounding urban areas, unlike their rural blue-eyed counterparts. Regardless of the color, researchers have now demonstrated that Arctic reindeer really do have a kind of magic in their eyes…just in time for Christmas.
By Michele Wessel