I am Rangifer tarandus. It's winter here and the days are so short that I don't see sunlight for months. I am the only mammal whose eyes are known to change color in response to the seasons. A reflective layer behind my retinas changes from gold in the summer to blue in the winter. This change in color helps my eyes capture more light during the dark winter months at my extreme latitude.
Looking for a Clue?
Half of the Mystery Classes are located in my hemisphere.
Photo: CreativeCommons/W. Baxter