1. Reindeer and caribou are the same thing
Historically, the European/Asian reindeer and American Caribou were considered to be different species, but they are actually one and the same. There are two major groups of reindeer, the tundra and the woodland, which are divided according to the type of region the animal lives in, not their global location. The animals are further divided into subspecies, ranging from nine to 13 depending on who is doing the classification. At least one subspecies, the Arctic Reindeer, is already extinct. (The reindeer/caribou thing could technically get more complicated in the future — check out this Discovery News article for more details.)
2. They go by many names, all of which seem appropriate
Reindeer comes from the Old Norse word "hreinin," which means "horned animal." Caribou is based on the French word for "snow shoveler," in reference to the animal's habit of digging through the snow for food. In many Eastern European languages, the root word for the creature comes from an Iranian word meaning "cattle." This makes sense given that the animals were semi-domesticated in these areas and used for meat, fur, milk, and transportation.
3. Santa's reindeer are most likely the R.t. platyrhynchus subspecies from the Svalbard islands off of Norway
We know that because Clement C. Moore's poem, "A Visit from Saint Nicholas," which first introduced the world to Santa's reindeer, describes them as tiny. The only reindeer that could really be considered tiny are the Svalbard subspecies, which weigh about half as much as the average reindeer species and are at least a foot shorter in length — that definitely proves useful when landing on roofs.
Strangely, you'll almost never see these guys in depictions of Santa, as live-action films usually use full-sized reindeer and animations usually draw the creatures as a cross between a regular deer and a reindeer.
4. It's not always easy to tell the sex of a reindeer
In most deer species, only the male grows antlers, but that's not true for most reindeer. Although the females in certain populations do not have antlers, many do. During certain times of year, you can still tell the sex of a reindeer by checking for antlers. That's because males lose their antlers in winter or spring, but females shed theirs in the summer. The females are significantly smaller than the males, but you may get thrown if you come across a particularly large female or a small male.
5. Santa's reindeer may or may not be female
Since reindeer shed their antlers at different points of the year based on their sex and age, we know that Santa's reindeer probably aren't older males, because older male reindeer lose their antlers in December and Christmas reindeer are always depicted with their antlers. That means Santa's sled either has to be pulled by young reindeer, constantly replaced as they start to age, or Santa's reindeer are female. Do you want to imagine a rotating crop of sleigh pullers or an all-female lineup? It's up to you.
6. Reindeer were originally connected to Santa through poetry
Before Moore wrote A Visit from Saint Nicholas (aka The Night Before Christmas) in 1823, no one thought about reindeer in conjunction with Santa Claus. Moore introduced the world to Dasher, Dancer, Prancer, Vixen, Comet, Cupid, Dunder, and Blixem (the last two of which were later changed from Dutch to German, becoming Donner and Blitzen). While the first six names all make sense in English, the last two actually mean "thunder" and "lightning," respectively.
As for little Rudolph, he wasn't introduced until Robert L. May wrote a children's book in verse for Montgomery Ward in 1939 titled Rudolph the Red-Nosed Reindeer. Rudolph's name means "famous wolf" in German.
7. Reindeer are the only mammals that can see ultraviolet light
While human vision cuts off at wavelengths around 400 nm, reindeers can see up to 320 nm. This range only covers the part of the spectrum we can see with the help of a black light, but it is still enough to help reindeer see things in the glowing white of the Arctic that they would otherwise miss. Things like white fur and urine are difficult, even impossible, for humans to see in the snow, but for reindeer, they show up in high contrast.
8. Reindeer are ideally designed for life in hostile, cold environments
Life in the tundra is hard, but reindeer have it easy thanks to their amazing evolutionary enhancements. Their noses are specially adapted to warm the air they breathe before it enters their lungs and to condense water in the air, which they then use to keep their mucous membranes moist. Their fur traps air, which not only helps provide them with excellent insulation, but also keeps them buoyant in water, which is critical being as how they often travel across massive rivers and lakes while migrating.
Even their hooves are special. In the summer, when the ground is wet, their foot pads are softened, providing them with extra traction. In the winter, though, the pads tighten, revealing the rim of their hooves, which is used to provide traction in the slippery snow and ice.
9. While not all reindeer migrate, some of them travel further than any other migrating terrestrial mammal
A few populations of North American reindeer travel over 3,100 miles per year, covering around 23 miles per day. At their top speed, these reindeer can run 50 miles per hour and swim at 6.2 miles per hour. During spring, the migration herds range from 50,000 to 500,000 individuals, but during the winter the groups are much smaller as the reindeer have entered mating season and competition between the bucks begins to split up the crowds. Like many herd animals, the calves learn to walk fast — within only 90 minutes of being born, a baby reindeer can already run.
10. Reindeer played an important role in the survival of many cultures
In Scandinavia and Canada, reindeer hunting helped keep tribes alive, from the Mesolithic and Neolithic periods all the way through modern times. In Norway, it is still common to find reindeer trapping pits, guiding fences and bow rests dating from all the way back to the Stone Age. And in Scandinavia, reindeer is still a popular meat, sold in grocery stores in fresh, canned and dried forms. Almost all of the animal's organs are edible and many are crucial ingredients of traditional dishes in the area.
In North America, the Inuit people still use the creature as they have for thousands of years, for food, clothing, shelter, and tools. Many of these tribes still follow traditional practices that prevent selling the meat and limit the number they may kill on each hunting trip.
11. They used to live a lot farther south.
While reindeer now live exclusively in the northern points of the globe, when the earth was cooler and humans were less of a threat, their territory was larger. In fact, reindeer used to live all the way down in Nevada, Tennessee, and Spain during the Pleistocene area. Its habitat has shrunk considerably in the last few centuries. In the 19th century, reindeer still lived in Southern Idaho.
As for how nine reindeer manage to fly while pulling a sled carrying presents for every child in the whole world, science still hasn't worked that out.
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