Reindeer Eyes Change Color in Wintertime

By: By Michele Berger

Published: November 8,2013

 

 

 

 

Reindeer are exposed to darkness for months at a time. Researchers have now discovered how the animals' eyes adjust. (Erling Nordøy)

Scientists in 2011 discovered that reindeer have a built-in AC system to keep from overheating in their natural fur coats. Recently, researchers found these mammals also have a unique way of coping with extremely dark Arctic winters: Their eyes change color.
During the sunny time in their habitat, reindeer have yellowish-gold eyes, but during the cold season, the eyes turn a noticeable hue of blue, a new study published in the Proceedings of the Royal Society B reported.
It’s because of changes in a light-reflecting tissue layer behind the retina, according to Science. “This structure, called the tapetum lucidum (Latin for ‘bright tapestry’), gives the eye’s light-sensitive neurons a second chance to detect scarce photons in low-light conditions. (The layer also produces the ‘eye shine’ that can make animal eyes appear to glow in the dark.)” In other words, it makes the eyes extremely sensitive to light.

Reindeer eyes change from gold (right) in summer to blue (left) in winter. (University College London)

“Most people are familiar with the way a cat’s eye reflects light back to enhance night vision. In fact many animals have this reflective layer,” said lead researcher Glen Jeffery, of the University College London Institute of Ophthalmology, in a news release. “Arctic reindeer possess this reflective layer, too.”(MORE: Stunning Photos of Animal Eyes)
“This is the first time a color change of this kind in the eye has been shown in mammals,” he added.
To study the phenomenon, the research team looked at what Science described as disembodied reindeer eyeballs from Eurasian mountain reindeer anywhere from 1.5 to 3 years old. By weighing down the eyes, researchers recreated what happens to reindeer in the winter; because of the darkness, their eyes stay dilated, and this builds up pressure, making them up to 1,000 times more sensitive to light.
Not only does it better allow the animals to adjust to the different light extremes of the seasons, but it “gives them an advantage when it comes to spotting predators,” Jeffery said, “which could save their lives.”