According to a new study of Arctic reindeer (Rangifer tarandus), their eyes change color through the seasons from gold to blue to help animals spot predators in the winter whilst there is little light.

The study authors from Britain and Norway were interested in how these animals see in the perpetual darkness.

The Arctic reindeer has a layer of tissue in the eye called the tapetum lucidum which lies behind the retina and reflects light back through it to enhance night vision. By changing its color, the tapetum lucidum reflects different wavelengths of light.

In the bright light of summer the tapetum lucidum in Arctic reindeer is gold, similar to many other mammals, which reflects most light back directly through the retina. However by winter it has changed to a deep blue which reflects less light out of the eye. 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 scientists believe this would be an advantage in the prolonged murk of winter, allowing reindeer to more easily detect moving predators and forage.

“This is the first time a color change of this kind has been shown in mammals. By changing the color of the tapetum lucidum in the eye reindeer have flexibility to cope better with the extreme differences between light levels in their habitat between seasons,” said Dr Glen Jeffery from the University College London, who is the senior author of a paper published in the Proceedings of the Royal Society B.

“This gives them an advantage when it comes to spotting predators, which could save their lives.”

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Bibliographic information: Karl-Arne Stokkan et al. 2013. Shifting mirrors: adaptive changes in retinal reflections to winter darkness in Arctic reindeer. Proc. R. Soc. B, vol. 280, no. 1773; doi: 10.1098/rspb.2013.2451