What Is The Only Mammal Whose Eye Color Changes With The Seasons?

What Is The Only Mammal Whose Eye Color Changes With The Seasons? Arctic reindeer (Rangifer tarandus) exhibit a mesmerizing seasonal adaptation in the color of their eyes. This extraordinary revelation, detailed in a groundbreaking study titled “Reindeer eyes seasonally adapt to ozone-blue Arctic twilight by tuning a photonic tapetum lucidum,” published on June 29, 2022, sheds light on the remarkable ability of reindeer to adjust their vision to the ever-changing hues of their environment.

What Is The Only Mammal Whose Eye Color Changes With The Seasons?
What Is The Only Mammal Whose Eye Color Changes With The Seasons?
( Image By : nhm )

Arctic reindeer, known for their iconic presence in winter folklore, have long intrigued scientists with their seasonal eye color transformation. During the extended summer daylight, their tapetum lucidum, a reflective layer behind the retina, exhibits a captivating gold-turquoise hue. However, as the Arctic winter descends, with its prolonged darkness and blue-tinted twilight, the reflection transforms into a deep blue, making reindeer the only known mammals to undergo such a striking change.

Understanding the Atmospheric Phenomenon

The study delves into the atmospheric conditions that contribute to the extreme spectral change in the light environment of the Arctic. Reflectance spectroscopy is employed to analyze the photonic nanostructure responsible for the reflective region of the tapetum lucidum. The researchers propose a model explaining the reversible reformatting of the reflector, linking it to seasonal changes in the volume of interstitial fluid within the collagen fibrils forming the photonic crystal.

By allowing slow evaporation of the fluid from both summer and winter tapetum surfaces, coupled variations in fibril spacing and degree of order were observed, transforming the typical gold-turquoise color to a deep blue. This adaptation aligns with the peak spectral irradiance of the ozone-blue Arctic twilight, providing a unique insight into the mechanisms underlying this extraordinary phenomenon.

Adaptive Benefits and The Scientific Marvel of Reindeer Eyes

Increased visual sensitivity at the blue end of the spectrum during winter twilight enhances the reindeer’s ability for foraging and predator detection in the low irradiance conditions. The study suggests that this heightened sensitivity results from the general decrease in reflectance of organic materials towards shorter wavelengths, increasing their contrast against the snow’s high albedo.

A visit to the national eye collection at the Museum unveils the marvel of a bisected reindeer eyeball, showcasing the iridescent layer responsible for the color-changing spectacle. The tapetum lucidum, a mirrored layer behind the retina, aids the reindeer in seeing in the dark by reflecting light back towards the retina, giving it a second chance to detect incoming photons.

Why the Color Change?

As summer transitions to winter, the pressure inside the reindeer’s eye builds due to prolonged pupil dilation. This pressure squeezes fluid out of the tapetum lucidum, primarily composed of collagen fibers. The fibers then pack together more tightly, reflecting blue wavelengths instead of yellow. This dramatic shift in eye color renders the blue eyes over a thousand times more sensitive to light than their golden summer counterparts, perfectly adapting reindeer vision to the challenging Arctic habitat.

Human Emotion and Connection

The revelation of the reindeer’s unique eye adaptation evokes a sense of wonder and appreciation for the intricate ways in which animals adapt to their environments. The Arctic reindeer’s ability to thrive in extreme conditions, showcased through its eye color metamorphosis, adds a touch of sentiment to the scientific narrative.

Details In Short

  • Date of Study Publication: June 29, 2022
  • Subject of Study: Arctic reindeer (Rangifer tarandus)
  • Eye Color Transformation: Gold-turquoise in summer, deep blue in winter
  • Scientific Study: “Reindeer eyes seasonally adapt to ozone-blue Arctic twilight by tuning a photonic tapetum lucidum”
  • Atmospheric Conditions: Extreme spectral change in Arctic light environment
  • Scientific Method: Reflectance spectroscopy to analyze photonic nanostructure
  • Model Proposed: Reversible reformatting of tapetum lucidum linked to seasonal fluid changes in collagen fibrils
  • Adaptive Benefits: Increased visual sensitivity at the blue end aids foraging and predator detection
  • Visit to National Eye Collection: Bisected reindeer eyeball showcases the iridescent layer
  • Tapetum Lucidum’s Role: Reflects light back towards retina, enhancing vision in low-light conditions
  • Reason for Color Change: Pressure buildup due to prolonged pupil dilation in winter squeezes fluid out, causing collagen fibers to pack tightly and reflect blue wavelengths
  • Emotional Connection: Sense of wonder and appreciation for the reindeer’s adaptation to extreme Arctic conditions.


In conclusion, the Arctic reindeer’s eye color transformation stands as a testament to the marvels of nature and the intricate ways in which animals adapt to their surroundings. As we delve into the scientific revelations of this unique phenomenon, we find ourselves captivated by the beauty and resilience of the natural world.


Q: Why do reindeer have a gold-turquoise eye color in summer and a deep blue color in winter?

The color change is linked to the adaptation of the tapetum lucidum, a reflective layer behind the retina, responding to the seasonal changes in the Arctic light environment.

Q: How does the tapetum lucidum contribute to reindeer vision?

The tapetum lucidum reflects light back towards the retina, enhancing the reindeer’s ability to see in low-light conditions, particularly during the extended Arctic twilight.

Q: Are there other animals with similar eye adaptations?

The study suggests that other animals with similar tapeta may employ comparable mechanisms to adapt to prolonged changes in their light environment.

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