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.