To thrive in the dark, snowy Arctic winter, reindeer have unique visual systems. Their eyes change color to adapt to the dramatic shifts in sunlight between Arctic summer and winter, but may do even more to help them forage. A study published December 15 in the journal i-Perception found that their eyes might have evolved to see light in the ultraviolet spectrum to better locate their favorite food in their desolate home.
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Reindeer primarily eat Cladonia rangiferina (C. rangiferina), also known as reindeer moss, which is not actually moss but a species of algae-fungus. It forms a dense and crunchy blanket on the ground across the Earth’s northern latitudes and plays an important role in the ecosystem as a food source.
In the study, the team worked in the Cairngorms mountains in the Scottish Highlands, home to Britain’s only reindeer herd. Reindeer were locally hunted to extinction, but began to be reintroduced from Scandinavia in 1952. The Cairngorms are home to more than 1,500 species of lichen, but the reindeer here only rely on C. rangiferina during the winter months
“A remarkable characteristic of reindeer is their dependence on this one type of lichen,” study co-author and Dartmouth College anthropologist and evolutionary biologist Nathaniel Dominy said in a statement. “It’s unusual for any animal to subsist so heavily on lichens, let alone such a large mammal.”
When faced with snow, the white lichen is invisible to the human eye. However, co-authors Catherine Hobaiter and Julie Harris from the University of St. Andrews found that C. rangiferina and some other lichen species that supplement the reindeer diet absorb ultraviolet (UV) light. The team used spectral data from the lichen and light filters that were made to mimic reindeer vision and found that the plants may look like dark patches against a bright landscape to the reindeer. They stand out like Dalmatian spots and are easier for the reindeer to locate.
According to Dominy, this is one of the first studies to use a visual approximation of how these mammals may see their world.
“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.”
Some animals that can see on the UV spectrum include dogs, cats, pigs, and even ferrets. They generally do this with the short blue photoreceptors called cones present in their eyes.
