How do you find delicious treats in the snow? Ask the reindeer
There are a lot of myths about reindeer, and at least one of them is true: They live in remote areas way up north that get a lot of snow.
Living in that winter wonderland can be a challenge when your favorite food is white, but the animals have special vision that likely helps them find food easier – which could come in especially handy after a busy Christmas Eve.
"When I learned that reindeer have a very unusual visual system, I thought, well, that has to be an adaptation for finding food," said Nate Dominy, a professor of anthropology at Dartmouth College.
Dominy studies how animals find and eat their food. In a study published last week in the journal i-Perception, he and his colleagues found more evidence to explain the peculiar vision that reindeer have.
Finding food under ultraviolet light
Scientists have known for a while that reindeer's vision is special and that they can detect ultraviolet light, which can be harmful to human eyes.
"For reasons unknown, in reindeer, ultraviolet light can pass right through those tissues and make contact with the retina," Dominy said.
One potential explanation for this is protection from predators.
"To us humans, a white wolf on a snowy landscape would be difficult to see, but for a reindeer, it could be totally different because snow reflects ultraviolet light and the hair on wolves absorbs it," he said. "So, for a reindeer, a wolf would look much darker than it does to us."
That also applies to finding food. Reindeer are big animals that need a lot of energy, but their diet consists mostly of organisms called lichens – also known as reindeer moss.
"Lichens are this amazing lifeform. It's a symbiotic relationship between algae and fungi," Dominy said.
But some lichens are white and can get covered in snow during the winter. So in the study, the team focused on the particular lichens that reindeer eat. They wanted to see how the organisms' interaction with light affected how the reindeer would see them.
Dominy explained that, just like the wolves, lichen absorbs ultraviolet light, while snow reflects it. So for reindeer looking around for food, the lichens pop out against the white snow.
"If you're a reindeer and you can scan the distance and you can see way over there there's a patch of edible lichens, then you don't have to wander around," he said. "You can move in a straight line, conserve energy, get to that food resource and eat it."
Listen to All Things Considered each day here or on your local member station for more stories like this.
The team studied the diverse populations of lichens in Scotland. Their results add evidence to previously-held hypotheses that the reindeer's eyes have adapted to their environment to be able to find food easier.
"So we can show that [lichens] are indeed strong absorbers of UV light, and a lot of vegetation is right? So we just confirmed that lichens are a plausible explanation for their UV vision," Dominy said.
Extra help from adaptation
There is one more thing helping the reindeer: An extra layer in their retinas adjusts in the winter – when it's snowy and dark – to become more sensitive to that UV light.
Robert Fosbury, a retired astrophysicist who now studies the relationship between light and life, said that extra layer is common among many animals, but not its changeability.
"Reindeer vision is very special in that it's really the only animal that is known to dramatically change its visual capabilities between the winter and the summer. And that's particularly pertinent in the Arctic, of course," he said.
That's because more sensibility to UV light means better sight, making it easier to avoid predators or find food.
There's still more to learn about the reindeer's eyes, like whether eating those lichens can even protect them against potential damage from the UV light. In the meantime, Dominy said one definite way you and your kids can keep those special eyes healthy is with vitamin C, which has been shown to shield eyes from UV damage.
"When people have studied the eyes of reindeer, they found that there's a lot of vitamin C ... present in the eyeballs of reindeer, so that's another way to protect their eyes," he said.
So, if you want to put out some treats for reindeer who may visit your home, orange juice or carrots are a great option – as well as cookies for Santa.
Kathryn Fox and Gabe Spitzer contributed to this report. contributed to this story
Copyright 2023 NPR. To see more, visit https://www.npr.org.