Arctic Reindeers' Eyes Change Colors with the Seasons [VIDEO]

Arctic reindeers' eyes change colors with the season, shifting from gold to blue in order to adapt to extreme changes in light levels throughout the year.

Like many animals, Arctic reindeer have layer of tissue in their eyes called the tapetum lucidum (TL). Located behind the retina, the TL reflects different wavelengths of light by changing color.

When faced with the bright summer sun, the TL in Arctic reindeer turns gold, reflecting a significant portion of the light back through the retina. By winter, it plunges into a deep blue, restricting the amount of light reflected out of the eye.

This change, the researchers explain, causes more light to scatter through photoreceptors at the back of the eye, thereby increasing the retina's sensitivity during the dark winter months. Among other things, this increases the reindeer's ability to detect predators in the forage.

Exactly what causes the color change is unclear, though the researchers say it may be the result of a shift in pressure within the eyes. In the winter, pressure increases, preventing eyeball fluid from draining naturally and compressing the TL. This reduces the space between collagen in the tissue and causes it to reflect the shorter wavelengths of the blue light characteristic of Arctic winters.

According to Glen Jeffery, a researcher from the University College of London's Institute of Ophthalmology, the discovery is significant in understanding the differences between different kinds of mammals.

"This is the first time a colour change of this kind has been shown in mammals," he said. "By changing the colour of the TL in the eye reindeer have flexibility to cope better with the extreme differences between light levels in their habitat between seasons. This gives them an advantage when it comes to spotting predators, which could save their lives."

Jeffery's previous research revealed that Arctic reindeer can see ultraviolet, which they use to find food and detect predators. The blue reflection, he said, is likely designed to favor ultraviolet sensitivity.