The Science Behind Reindeers' Changing Eye Color


| LAST UPDATE 12/22/2022

By Amie Alfaro
Reindeer Winter Snow Trekking
Diana Robinson Photography via Getty Images

Rudolph may have a red nose, but he isn’t the only reindeer with a special attribute. In fact, all reindeer share this exceptional quality that sets them apart from every animal in the world. Their eyes change color with the season.

Scientists have long been stumped as to why this strange phenomenon occurs and have never been able to figure out why. In the winter months, their eyes will alter their structure in order to increase their ability to find food and run away from any lurking predator. They will turn a deep blue. Then, once the weather warms up and summer comes along, they will become more of a golden color. While reindeer are not the only animals who adapt to the winter months, they are the only animals in the world to present this structural change within their eyes. Yet, no one could figure out the science behind why their eyes change every season. It took an astrophysicist and a neuroscientist to finally team up with a bag of reindeer eyes to understand why this happens.

Summer Reindeer Eye Color
kjorgen via Getty Images
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Glen Jeffrey, a neuroscientist from the University College London, and Robert Fosbury, an astrophysicist at the European Southern Observatory, were behind the discovery. They were able to figure out that the eyes change to help reindeer see better and spot their prey during the long twilight months of the wintertime. However, how exactly they were making this change kept stumping them. Jeffrey and Fosbury studied reindeer eyes in the lab to investigate further. They observed that collagen fibers were floating around more loosely in summer eyes, whereas the collagen fibers were grouped together closely in winter eyes. The summer eyes would reflect a reddish light, while the winter eyes would reflect a blue light. The scientists also observed that the winter eyes had dilated pupils, but the summer eyes had normal pupils. Glen Jeffrey told National Geographic“What we’ve found is a really great biological mechanism that’s totally unique and bizarre – and makes perfect sense.”

Reindeer are a fascinating species. They are part of a Christmas tradition, along with cutting down trees and baking cookies for Santa. Now, scientists know a bit more about Santa’s favorite animals. Here is the complete study.

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