Rudolph does not need to use his famous red nose to guide his peers, because the animals have a special form of night vision that they use to search for food, the scientists concluded.
Researchers have studied why this species is the only mammal whose eyes change color depending on the season, ranging from golden orange in summer to a blue tint in winter.
The study found that while the color change may help them see better in the depths of winter, when snowfall is heavy, it also allows their eyes to transmit ultraviolet light.
Researchers said this raises further questions because the sun’s UV rays reflected from snow cause the species to absorb twice as much UV light due to their advanced eyesight.
They also stated that this was the reason why deer were able to see clearly in the dark and search for foods such as lichen.
The study was led by Professor Nathaniel Dominy, an anthropologist at Dartmouth College in the US, along with Dr Catherine Hobaiter and Professor Julie Harris from the School of Psychology and Neuroscience at the University of St Andrews.
Hobaiter said: “To our eyes, just like most mammals, the pale lichen in the white snow is incredibly difficult to spot. But to the reindeer’s eyes, the species they need to feed on would stand out as dark spots in the much more reflective snowy landscape.
Reindeer are known to feed on a particular species of lichen called Cladonia rangiferina, often colloquially called “reindeer moss”.
The lichen species, essential for reindeer survival, is not actually moss and grows in sponge-like beds in northern latitudes.
Hobaiter said it had previously been suggested that reindeer’s night vision might be an adaptation to lichen foraging, but previous tests found no substantial evidence.
However, she said there are more than 13,000 species of lichens in the world and to date no one has tested which species reindeer eat.
She said: “One of the amazing things about Scotland is that we have some of the richest diversity of lichens in the world – the Highlands are home to over 1,500 different species and the Cairngorms are home to a local flock of reindeer, reintroduced to Scotland after being hunted to extinction. Scotland is therefore the ideal place to try to finally solve the mystery.
The team began their search in March in the Cairngorms mountain range in the Eastern Highlands, looking for lichen beds. They photographed various lichen beds under UV light, finding that different species absorbed or reflected light differently and that “reindeer moss” strongly absorbed light.
Dominy said: “If you can put yourself in their shoes, looking at this white landscape, you would want a direct path to your food. Reindeer do not want to waste their energy searching for food in a cold and barren environment.
“If they can see the lichens from afar, that gives them a big advantage, allowing them to conserve precious calories at a time when food is scarce.”
PA Media contributed to this report
