Excessive UV light can damage retinas as in snow blindness. But a recent study shows that reindeer use UV as radar for their next meal.

Mammals typically see light from the visible spectrum, but UV shines in shorter wavelengths that are invisible to most mammals. Except reindeer.
Ice and snow reflect 90 percent of all UV light that hits it, while snow-free land, where the reindeer roam, only reflects around 5 percent.

Glen Jeffrey and company at the University of London wanted to know why and how reindeer used their UV powers.

In their study, they exposed the eyes of 18 anesthetized reindeer to various wavelengths of UV and visible light. (Guess where Santa’s sleigh isn’t going this year.) An electrode detected whether or not nerves in the eyes had fired when the lights were seen.

It’s All About Food

“Since migrating to the Arctic 10,000 years ago, these animals have adapted incredibly quickly,” says Jeffery.
To learn more, Jeffrey’s team explored parts of the reindeer’s range with a UV camera.
Here’s what they saw: animal urine – a sign of both predators and potential mates, and lichen, a go-to food for reindeer during winter. These elements all read black in contrast to the snowy UV reflecting snow
“Very few mammals see UV light. Rodents do and some species of bat do, but we have no idea why they have developed this capability,” says Jeffery. “This is the first time we have got a real handle on why a mammal uses UV light.”

In fact, the energy in UV light is strong enough to damage the eye’s sensitive photoreceptors and sometimes permanent damage. sometimes causes permanent vision loss. The eyes of most mammals cannot cope with UV light because it carries enough energy to destroy their sensitive photoreceptors, permanently damaging vision.

Now the big question for Jeffrey is “Why don’t reindeer, arctic fox, polar bears or arctic seals get snow blindness?” asks Jeffery. “Arctic mammals must have a completely different mechanism for protecting their retinas.” Stand by. Jeffrey and his team will be back to the Arctic, and maybe on the road to discovering human applications of their work.


New Scientist

Reindeer gained UV vision after moving to the Arctic.