Santa Claus doesn’t need to worry about his trusty reindeer getting lost in the vast Arctic wilderness or failing to see where they need to go. These animals possess a unique form of night vision. As the cold sets in, Arctic reindeer change the color of their eyes from golden to a deep blue. This adaptation allows them to perceive ultraviolet light, making it easier for them to locate lichen—a vital food source for their survival. This remarkable aspect of reindeer vision was revealed by a team of American and Scottish scientists. The research was led by Professor Nathaniel Dominy, an anthropologist from Dartmouth College (USA), along with Dr. Katherine Hobaiter and Professor Julie Harris from the School of Psychology and Neuroscience at the University of St Andrews (UK).
What the Researchers Discovered
The scientists uncovered why reindeer are the only mammals that change their eye color with the seasons: from a golden-orange hue in summer to a dark blue during the winter months. The team said this color change helps the animals pick out ultraviolet light and find their primary food—reindeer moss—but it also raises other questions. Because sunlight reflected off the snow causes reindeer to receive twice as much ultraviolet light, the extra UV can complicate their foraging. “To our eyes, as well as the eyes of most mammals, pale lichen on white snow is incredibly difficult to spot. But for reindeer, the lichen they feed on appears as dark patches against the snowy landscape,” explained Dr. Katherine Hobaiter.
Reindeer eat a specific lichen, Cladonia rangiferina, commonly called reindeer moss. It’s not actually a moss; it grows like a spongy shrub in northern latitudes.
There are more than 13,000 species of lichen worldwide. Scotland is home to a region with over 1,500 lichen species: the Highlands. In the eastern Highlands, inside the Cairngorms mountain range and national park, many reindeer live. During their research, the team photographed lichen in the Cairngorms under ultraviolet light and found that different species absorb or reflect UV in different ways. Reindeer moss absorbs UV to an extreme degree, The Guardian reported.
Nathaniel Dominy says reindeer don’t want to waste energy wandering the cold expanses in search of food. “If they can see lichen from a distance, it gives them a significant advantage, as they conserve precious calories when food is scarce,” the professor added.
