Reindeer Evolved to See UV Light to Spot Food in Arctic Winters

The ability to see ultraviolet light helps reindeer locate their primary food source, a type of lichen, against the bright, snowy landscape.

Reindeer have evolved to see light in the ultraviolet (UV) spectrum, which helps them spot their primary food source, a type of lichen known as Cladonia rangiferina, during dark and snowy Arctic winters.
The lichen, often referred to as 'reindeer moss', absorbs UV light and appears as dark patches against the bright, snowy landscape, making it easier for reindeer to locate.
Reindeer eyes change color between seasons, transitioning from golden in the summer to a vivid blue in the winter. This blue color is thought to amplify the low light of polar winter and allows up to 60% of UV light to pass through to the eye's color sensors.
The ability to see UV light has been a long-standing scientific mystery, as UV light reflects off of every snow-covered surface. However, this study suggests that the answer is tied to the lichen, which does not reflect UV light.
Given the importance of lichens in the reindeer diet, it is possible that the animal's eyes are optimized to single out this food staple at the time of year it would be most difficult to find.