Reindeers' eyes change color from a deep gold to crisp blue depending on the season.
The animal's eyes are gold in the well-lit summers, and blue in the dark winters.
Researchers concluded the Arctic dwelling reindeers' eyes change to help them see better in constant sunlight or continuous darkness, a Biotechnology and Biological Sciences Research Council news release reported. The phenomenon changes the retina's sensitivity to light.
Many mammals including the reindeer have tapetum a layer of optic tissue called the tapetum lucidum (TL). This tissue is located behind the retina, and its purpose is to reflect light which enhances the ability to see in the dark.
When the animal's eyes turn blue it causes the TL to reflect different light wavelengths.
"This change scatters more light through photoreceptors at the back of the eye, increasing the sensitivity of the retina in response to the limited winter light," the news release reported.
The team believes the change gives the reindeer and advantage during the dark winters because it allows them to see better while foraging.
"This is the first time a [color] change of this kind has been shown in mammals. By changing the [color] of the TL in the eye reindeer have flexibility to cope better with the extreme differences between light levels in their habitat between seasons," Lead researcher Professor Glen Jeffery from UCL, said. "This gives them an advantage when it comes to spotting predators, which could save their lives."
The change could take place as a result of pressure inside of the reindeer's eyes. During the winter the animal's eyes are under more pressure, which is believed to cause constant pupil dilation. This would prevent fluid from easily draining from the eyes.
When there is more fluid in the eyes it puts more pressure on the TL, which reduces "the space between collagen in the tissue and thus reflecting the shorter wavelengths of the blue light common in Arctic winters."
