Rudolph didn’t need to use his famous red nose to guide his fellow reindeer, as the animals have a special form of night vision that they use to search for food, scientists have concluded.
Researchers looked at why the species are the only animals whose eyes change color depending on the season, from golden orange in the summer to a blue tint in the winter months.
The study found that while the color shift may help them see better in the peak of winter when snowfall is heavy, it also allows their eyes to emit ultraviolet light.
Researchers said this raises further questions, as the sun’s UV rays reflecting off the snow results in the species taking in twice as much UV light due to their advanced vision.
They also said that this is the reason why the deer can see clearly in the dark and search for food items such as lichen.
The study was led by Prof Nathaniel Dominy, an anthropologist at Dartmouth College in the US, and Dr Catherine Hobaiter and Professor Julie Harris from the University of St Andrews’ School of Psychology and Neuroscience.
Hobaiter said: “To our eyes, just like to most mammals, pale lichen in white snow is incredibly difficult to spot. But to reindeer eyes, the species they must feed on will stand out as dark spots in the much more reflective snowy landscape.”
Reindeer are known to feed on a specific type of lichen called Cladonia rangiferina, often referred to generically as “reindeer moss”.
The lichen species, essential to reindeer survival, is not actually moss and grows in spongy beds across the northern latitudes.
Hobaiter said it had previously been suggested that reindeer’s night vision might be an adaptation to forage for the lichen, but previous tests had not found substantial evidence.
However, she said there are more than 13,000 species of lichen worldwide and to date no one has tested the species the reindeer are feeding on.
She said: “One of the great things about Scotland is that we have some of the richest lichen diversity in the world – the Highlands are home to over 1,500 different species, and the Cairngorms are home to a local herd of reindeer that were reintroduced to Scotland after being hunted to extinction. So, Scotland is the perfect place to finally try to solve the mystery.”
In March, the team began researching the Cairngorms mountain range in the eastern Highlands in search of lichen beds.
The team photographed various lichen beds under UV light and found that different species absorb or reflect the light differently, and that “reindeer moss” strongly absorbs the light.
Dominy added: “If you can sit in their hooves and look at this white landscape, you’ll want a direct route to your food. Reindeer don’t want to waste energy wandering around looking for food in a cold, barren environment.
“If they can see lichens at a distance, it gives them a huge advantage, allowing them to save precious calories at a time when food is scarce.”
PA Media contributed to this report
