Reindeer are fascinating animals that live in high-latitude areas where long and dark winters are common. One of the most interesting features of reindeer is that their eye color changes with the seasons.

In the summer, reindeer's eyes shine golden and turquoise, resembling opals, while in the winter, their eyes turn dark blue.

Scientists have been studying this phenomenon for years and have discovered that it has to do with the reindeer's living environment. To find food and avoid predators in the snow, reindeer change the structure of the Tapetum lucidum, a tissue in the eyeball that reflects visible light to the retina and enhances light reception by photoreceptors.

By increasing the reflectivity of the Tapetum lucidum, reindeer can see the ultraviolet wavelength range, which helps them spot food and predators.

Glenn Jeffery, a neuroscientist at University College London, says, "We've discovered a great biological mechanism that's unique and bizarre and makes perfect sense." The color of the Tapetum lucidum varies in different animals, which is why the eyes of cats or raccoons glow eerily at night.

Reindeer live in the cold temperate coniferous forest and are semi-wild. They feed on litmus, Field horsetail, mushrooms, as well as young branches and leaves of woody plants.

One of the most impressive characteristics of reindeer is their annual migration of hundreds of kilometers. As soon as spring arrives, they leave the forests and grasslands of the subarctic regions where they spend the winter and head north along the same route for hundreds of years.

The females lead the way, followed by the males, and they travel day and night, eating while walking. Along the way, they shed their thick winter fur and grow a new, thinner summer coat. The fluff that falls off serves as a road sign.

Reindeer always move forward at a constant speed, except when they are disturbed by wolves or chased by hunters. In those cases, they run for a while, making earth-shattering noises and raising dust all over the sky.

Young reindeer grow faster than any other animal. The doe conceives in winter and gives birth during the spring migration. The cubs can travel with the doe two or three days after birth, and after a week, they can run as fast as their parents, reaching a speed of 48 kilometers per hour.

There are significant differences in morphology between the different reindeer subspecies. Generally, reindeer living in southern regions are larger than their northern counterparts. The shoulder width of reindeer can reach 120 centimeters, and the body length ranges from 1.5 meters to 2.3 meters. Both males and females have horns on their heads, which is one of the distinctive features that distinguish reindeer from other deer species.

Reindeer's annual migration and rapid growth make them even more extraordinary. Studying reindeer helps us understand the complexity and beauty of the natural world.