In humans, eye color is nothing but a permanent genetic trait. But in reindeer, it changes with the season. . The color changing ability comes not because of a difference in temperature, but as an adaptation to handle the Arctic's semi-permanent night. Like cats in a pair of headlights, reindeer have eyes that reflect light - but in the extended darkness, their eyes become strained. As pressure builds from forcing their pupils to dilate for months at a time, the part of the eye that bounces back light constricts, subsequently reflecting blue light rather than yellow light. The color change isn't just for show, though - once the eyes turn blue, they are over a thousand times more sensitive to light (making them well-equipped to handle the dark winter). . It's worth noting that the color change isn't incredibly stark on first glimpses. The color change isn't seen in the iris (like how our eyes are colored), but rather the tapetum lucidum (an area in the back of the eye). . . Read more about the color-changing marvel: https://www.nhm.ac.uk/discover/colour-in-collection-reindeer-eye.html . Graphic shows a pair of yellow eyes and a pair of blue eyes, along with icons for day and night. The factoid reads: "Reindeer have eyes that reflect blue in the winter, making them 1000 times more sensitive to light." . Pixel Planet Today is created by @Terrabyte. Give us a follow and keep up with the other stuff we're doing. 🌎❤️ . . #christmasfacts #christmasanimals #arcticanimals #reindeer #animalfacts #animalart #pixelplanet #pixelplanettoday #terrabyte #pixelart #planetfacts #artivism #climatedesign