There are many myths about reindeer, and at least one of them is true: They live in remote areas in the north where there is a lot of snow.
Living in that winter wonderland can be a challenge when your favorite food is white, but animals have special vision that probably helps them find food more easily after a busy day. which is Christmas Eve.
“When I learned that reindeer have a unique visual system, I thought, well, that must be an adaptation for finding food,” said Nate Dominy, a professor of anthropology at Dartmouth College.
Dominy studied how animals find and eat their food. In a study published last week in the journal Perceptionshe and his colleagues found more evidence to explain the extraordinary vision of the reindeer.
Finding food under ultraviolet light
Scientists have known for a long time that reindeer have special vision and can detect ultraviolet light, which is harmful to human eyes.
“For unknown reasons, in reindeer, ultraviolet light can pass right through the tissues and make contact with the retina,” Dominy said.
One potential explanation for this is protection from predators.
“For us humans, a white wolf in a snowy landscape is difficult to see, but for a reindeer, it can be very different because the snow reflects ultraviolet light and the hair of wolves ingest it,” he said. “So, for a reindeer, a wolf looks darker than us.”
That also applies to finding food. Reindeer are large animals that require a lot of energy, but their diet usually consists of organisms called lichens also known as reindeer moss.
“Lichens are this amazing life form. It’s a symbiotic relationship between algae and fungi,” Dominy said.
But some lichens are white and can be covered with snow during winter. So in the study, the team focused on the particular lichens that the reindeer eat. They wanted to see how the organisms’ interaction with light affected how the reindeer saw them.
Dominy explains that, like foxes, lichen absorbs ultraviolet light, while snow reflects it. So for reindeer looking for food, the lichens stand out against the white snow.
“If you’re a reindeer and you can scan the distance and you see the path there with a patch of edible lichens, then you don’t need to roam,” he said. “You can move in a straight line, conserve energy, get to that food resource and eat it.”
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The team studied different lichen populations in Scotland. Their results add evidence to previously held hypotheses that reindeer eyes have adapted to their environment to make it easier to find food.
“Let’s show that [lichens] actually strongly absorb UV light, and many of the plants right? So we confirmed that lichens are a plausible explanation for their UV visibility,” Dominy said.
More help from customization
There’s one more thing that helps reindeers: An extra layer on their retinas adjusts in the winter when it’s snowy and dark to be more sensitive to UV rays.
Robert Fosbury, a retired astrophysicist who now studies the relationship between light and life, said that the extra layer is common in many animals, but not its variability.
“The vision of the reindeer is very special because it is the only animal known to change its visual capabilities between winter and summer. And that is especially important in the Arctic, of course,” said he.
That’s because greater sensitivity to UV light means better vision, making it easier to avoid predators or find food.
There is still much to learn about reindeer eyes, such as whether eating lichens can protect them against potential damage from UV light. In the meantime, Dominy said that one sure way you and your children can keep those special eyes healthy is vitamin C, which has been shown to protect the eyes from UV damage.
“When people studied reindeer eyes, they found that there is a lot of vitamin C … which is in the reindeer’s eyeballs, so that’s another way to protect their eyes,” he said.
Therefore, if you want to put some food for the reindeer that may visit your house, orange juice or carrots are a good choice as well as cookies for Santa.
Kathryn Fox and Gabe Spitzer contributed to this report.
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