“Reindeer have an amazing visual system. This is unlike any other mammal we know of,” said college professor Nathaniel Dominy.
Why don’t reindeer suffer from snow blindness?
More than 10 years ago, Norwegian scientists published an article in the journal The Royal Society in which they shared their discovery – deer are able to change eye color depending on the time of year. In summer, the animals’ eyes are golden-yellowish, but with the onset of the polar night they take on a rich, dark blue color.
This metamorphosis, the researchers believe, allows deer to see in the dark, enhancing the weak light of the polar winter, and also to adapt to the transition from the polar night to the world of blinding light when the sun’s rays reflect off the white snow.
“Most animals that are active in daylight want to avoid ultraviolet light. Ultraviolet radiation is harmful. Because snow reflects ultraviolet light, which is a problem that causes snow blindness in people without sunglasses,” Dominy said.
Reindeer do not suffer from snow blindness, but they also pay for this unique opportunity with their health. Biologists said that when the tapetum (layer of the choroid) of a deer is colored blue, 50% less light is reflected from its eye than during the “golden” period. And although the eyes become 1000 times more sensitive to light, visual acuity still decreases. During the long polar night, the deer’s pupils remain dilated, so from such muscle tension the animal begins to develop glaucoma.
Why do deer have such strange vision?
According to Professor Dominy, in the new research, scientists set a new goal, to understand why deer developed the ability to see light in the ultraviolet spectrum. Some believe that reindeer’s vision evolved so that they could protect themselves from predators, such as being able to spot white wolves against a snowy landscape. Others – to save energy while searching for food.
Nathaniel Dominy explained that reindeer primarily feed on reindeer moss (aka moss), which is actually considered a fruticose lichen. So the researchers headed to the Cairngorms Mountains in the Scottish Highlands, home to more than 1,500 species of lichen, as well as a herd of reindeer. It turns out that deer’s favorite food absorbs ultraviolet light.
“Reindeer moss absorbs ultraviolet light, which means that the white lichen that people have difficulty seeing against the snow stands out as dark spots to animals,” the AP reports.
Lichens are also believed to have antioxidant properties, and reindeer eyes are high in vitamin C, which is beneficial for repairing damaged cells, according to Dominy. Perhaps these facts are interconnected, the professor believes.