Reindeer Eyes Turn Blue as Christmas Nears

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The fictional Rudolph had a shiny nose to cope with winter darkness, but real-life reindeer possess some magic of their own. Part of the reindeer eye shifts from gold to winter blue, improving their ability to use light when the days become shorter, according to a new study.

The study, published in the latest Proceedings of the Royal Society B, helps to explain how Arctic reindeer continue to see in near darkness.

The part of the eye that changes color is the tapetum lucidum, commonly known as the ‘cat’s eye.’ It resides under an unpigmented part of the retina.

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“In summer, it is golden with most light reflected back directly through the retina, whereas in winter it is deep blue with less light reflected out of the eye,” wrote Karl-Arne Stokkan, of the University of Tromso in Norway, and colleagues.

Stokka was able to study reindeer right at the university. Several were brought in from mountain region herders. They were maintained in large outdoor pens. The researchers studied their eyes during two weeks on either side of the summer and winter solstices.

The blue reflection in winter is associated with significantly increased retinal sensitivity, they explained. It may scatter light, which could force the eye to work harder, thereby improving the sensitivity.

It’s not a perfect system, though.

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“Increased sensitivity occurs at the cost of reduced acuity, but may be an important adaptation in reindeer to detect moving predators in the dark Arctic winter,” the researchers explained.

Unfortunately for reindeer, they are good eats for all kinds of carnivores, including some humans.

Another study, conducted earlier this year at the same university, found that reindeer meat is one of the healthiest, leanest meats around. It has nearly double the amount of nutrients of other more common meats, and yet its fat content is comparable to that of a chicken.

At least this eye adaptation, which sounds like something Santa himself would have come up with, gives reindeer a chance to see the predators coming and to high tail it out of there.

Image: Kia Hansen