• Posted December 22, 2023

Santa's Reindeer Evolved to Better Spot Their Favorite Food

No glowing red nose required: Real reindeer don't need Rudolph's help to find the Arctic food they love most, new research shows.

If you're a reindeer, your go-to favorite food is a humble moss-like lichen called Cladonia rangiferina, explained researchers at Dartmouth College in Hanover, N.H.

Trouble is, in the darkness of a northern winter spotting the lichen can be really tough.

Luckily, the eyes of countless generations of reindeer have evolved to see light on the ultraviolet (UV) spectrum.

C. rangiferina does not reflect UV light; it instead absorbs it, the researchers pointed out. Reindeer eyes have evolved to pick up on that.

"Reindeer are so cool, but many people think about them only at Christmas," study first author and anthropology professor Nathaniel Dominy said in a Dartmouth news release. "Now is a good time to alert people to their extraordinary visual system."

To the human eye, C. rangiferina appears to disappear into the landscape, especially in hours ruled by darkness. However, working with researchers from St. Andrews University in Scotland, Dominy helped discover that the lichen absorbs UV light.

This means that, to the reindeer's eye, C. rangiferina stands out easily amid other Arctic mosses, lichens and grasses. The lichen appears as darker patches against a light background.

"If you can put yourself in their hooves looking at this white landscape, you would want a direct route to your food," Dominy said. "Reindeer don't want to waste energy wandering around searching for food in a cold, barren environment. If they can see lichens from a distance, that gives them a big advantage, letting them conserve precious calories at a time when food is scarce."

What's more, prior studies found that reindeer's eyes actually change over the course of a year, becoming more adept at seeing the blue range of winter light during that season.

"If the color of the light in the environment is primarily blue, then it makes sense for the eye to enhance the color blue to make sure a reindeer's photoreceptors are maximizing those wavelengths," Dominy explained.

The study was published Dec. 15 in the journal i-Perception.

Overall, nature has endowed reindeer with the ability to pick out their favorite food source at precisely the time of the year when it's usually toughest to spot.

So, even if Rudolph's shiny nose helps guide Santa, "it is Rudolph's blue eyes that allow him to find dinner after a long Christmas season," the researchers wrote.

More information

Find out more about reindeer at the San Diego Zoo.

SOURCE: Dartmouth College, news release, Dec. 15, 2023