Post-flight feast: Study suggests reindeer vision evolved to spot favorite food

CONCORD, N.H. — Rudolph the Red-Nosed Reindeer may have millions of carrots ready for him on Christmas Eve, but what about the rest of the year?

Finding food in a cold, arid landscape is a challenge, but researchers from Dartmouth College in New Hampshire and the University of St. Andrews in Scotland report that reindeer eyes may have evolved to allow them to easily detect their preferred food.

It’s further proof that while reindeer are famous for pulling Santa’s sleigh, it’s their vision that really sets them apart, says Nathaniel Dominy, a Dartmouth anthropology professor and co-author of a recent study published in the journal i -Perception.

“They’ve been kind of obscure and underheralded in the annals of visual neuroscience, but they’re having their moment because they have a really fascinating visual system,” he said in an interview.

Scientists have known for years that the mirror-like tissue in reindeer eyes changes color from a greenish gold in the summer to a deep blue in the winter, a process believed to amplify the low light of the polar winter. . But they weren’t sure what to make of another curious fact: unlike other mammals, reindeer can see light in the ultraviolet spectrum.

“Most animals that are active under daylight conditions want to avoid ultraviolet light. UV light is harmful,” Dominy said. “Snow reflects ultraviolet light, which is a problem, which is why humans suffer from snow blindness.”

Some scientists believe that reindeer vision evolved to protect the animals from predators, allowing them to spot white wolves in a snowy landscape, for example. The new study points to another possibility: diet.

Reindeer subsist largely on light-colored moss, which is not actually a moss but rather a type of lichen that grows in crunchy, carpet-like patches in northern latitudes.

The researchers traveled to the Cairngorms mountains in the Scottish Highlands, which are home to more than 1,500 species of lichen and Britain’s only herd of reindeer. They discovered that reindeer moss absorbs ultraviolet light, meaning that the white lichen that humans have trouble seeing against the snow stands out as dark spots to the animals.

“If you are a reindeer, you can see it and you have an advantage because then you don’t wander around the landscape. You can walk in a straight line and get to that food, and in the process you conserve energy,” Dominy said. “These animals are desperate for food, and if they can find enough lichens, then they have an advantage.”

Juan José Negro is specialized in evolutionary ecology and conservation biology at the Higher Council for Scientific Research. While his focus is primarily on birds of prey, he found the new research on reindeer intriguing.

“I love every piece of work that is about color and vision,” she said. “Every time I read other people’s works, there is something that generates new ideas. …And in the case of reindeer, this leads me to want to pay more attention to this part of the spectrum.”

While he didn’t see any immediate biomedical benefit to the research, such work is useful in improving understanding of how animals cope with difficult environments, he said.

Dominy echoed that point, but said it also has human implications. Much pharmacological research has been done on lichens because they have antioxidant properties. Reindeer eyes that let in ultraviolet light suggest there might be some mechanism to protect them from harm, he said.

“Reindeer eyes are full of ascorbic acid, or vitamin C, and vitamin C is great for repairing damaged cells,” he said.

With that in mind, Dominy is updating the advice he offered after writing a 2015 article exploring why a reindeer’s red nose would be ideal for guiding Santa’s sleigh.

Back then, he recommended children give up Rudolph cookies and other high-calorie foods to compensate for the body heat lost through the nose. Now, he says, focus on his eyes and save the milk and cookies for Santa.

“The best thing you could give them to protect the health of their eyes would be something rich in vitamin C,” he said. “Orange juice, carrots, they would be perfect treats for the reindeer on Christmas Eve.”