Not Only Rudolph’s Nose Changes Color

Reindeer change eye color 1

New research at the University of Tromsø – Norway’s Arctic University – shows that reindeer eyes change color from yellow-green in summer to deep blue in winter.

Reindeer eyes work the same way as the eyes of a cat when it comes to reflecting light in the darkness. The reflection in reindeer’s eyes is yellow-green in summer and deep blue in winter, an ability that is not found in any other animal.

– Our study reveals that reindeer’s eyes are specially adapted to the lighting conditions that characterize northern latitudes.  This has never before been discovered because no one has studied animals experiencing extreme lighting conditions throughout the year, says Professor Karl-Arne Stokkan to

 (article continues)Reindeer change eye color 2

No – it is not a kaleidoscope but reindeer eyes..

Advanced Pumping System

Behind the retina, several animals have a light-reflecting surface named tapetum lucidum.

This surface reflects light so that the animals see better in the dark. It is the structure of this surface that changes color when darkness falls in the winter.

– It is the fact that a cell pump pumps fluid into the eye. The only way the liquid can come out is through a good drainage system behind the eye, says Stokkan to the university’s website.

– The difference in the eye pressure from summer to winter is significant. The fibers in the reindeer’s tapetum come closer together because of this pressure, and thus changing the reflected color. This leads to increased sensitivity because blue light is spread more than yellow light, he continues.

Better Shadow Sight

Since the blue light is more scattered than yellow light, the light is spread in a different way into the retina when the reindeer’s eyes are blue. More light receptors are stimulated simultaneously.

According to the article on, this leads to a blurring image and the vision actually gets worse. The advantage is that in the winter the animals get considerably more sensitive to predators moving in the dark.

Reindeer change eye color 3

The reindeer were sedated before the eyes were stimulated to examine why the eye color changed. Researchers at the University of Tromsø – Norway’s Arctic University look upon research on the reindeer’s eye as curiosity-driven research, with no immediate application.


Text by: Thor Bugge Lanesskog, ThorNews


Photos from top by: Martti Kainulainen / UiT/AFP, Institute for Arctic and Marine Biology / UiT, Andreas Palmén / UiT

Categories: Nature, Quirky

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