Reindeer eyes change color — they’re golden in summer and blue in winter.

Original photo by Cappan/ iStock

Rudolph’s nose may have been red, but his eyes were blue — except in the summer, when they would have been golden. That’s because reindeer eyes change color depending on the time of year, which helps them see better in different light levels. Their blue eyes are approximately 1,000 times more sensitive to light than their golden counterparts, a crucial adaptation in the dark days of winter. Only one part changes color, however: the tapetum lucidum, a mirrored layer situated behind the retina. Cats have it, too — it’s why their eyes appear to glow in the dark. This part of the reindeer retina shines a different hue depending on the season.

Male and female reindeer both grow antlers.

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Unlike other members of the Cervidae (read: deer) family, both male and female reindeer have antlers. They have this in common with bovids (goats, sheep, and antelopes), whose females use their horns like female reindeer use their antlers: to protect their food and territory.

Rudolph and his eight friends aren’t the only animals with unique eyes. Chameleons can move theirs independently of one another, giving them nearly 360-degree views of their surroundings; goats’ distinctive regular pupils give them a panoramic view of the horizon, allowing them to detect predators early; and cuttlefish pupils resemble a “W” in bright light and a circle in the darkness of deep waters — to name just a few unusual animal peepers. Maybe those critters should get songs written about them, too.

Numbers Don't Lie

Miles some North American reindeer migrate each year

3,000

First airing of “Rudolph the Red-Nosed Reindeer,” the longest-running Christmas special

1964

Pounds of food an adult reindeer can eat in a single day

Reindeer in the Arctic National Wildlife Refuge’s Porcupine caribou herd

200,000

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Caribou, another word for reindeer, means “______.”

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Caribou, another word for reindeer, means “snow shoveler.”

Rudolph was created for a department store.

Long before he made his television debut, Rudolph graced the pages of a coloring book handed out to children visiting Santa Claus at Montgomery Ward department stores. Catalog copywriter Robert L. May was commissioned to create a memorable character for those books in 1939, and his creation was wildly successful — 2.4 million copies were given out the first year alone. This was despite the fact that May’s boss initially disliked Rudolph’s red nose because it could imply that the animal had been drinking. Rudolph was a household name within a decade, with the song we all know and love (which happens to have been written by May’s brother-in-law) recorded by none other than Gene Autry in 1949. He really did go down in history.