Ho ho ho, Merry Christmas! Santa is preparing his sled and reindeer to deliver presents to children across the world tonight, but have you ever wondered how this iconic Christmas image came about?

Santa Claus' official hometown is Lapland in Finland, where the reindeer is the most common mammal of its family. Given that they live in the Arctic circle, reindeer have a thick fur coat to keep them warm in extremely cold weather. Their hollow, air-filled fur even enables them to float in water if needed. Reindeer are able to travel long distances in the snow without starving and can feed on lichen, which is poisonous to most animals. All these features make reindeer the perfect choice for Santa's sled.

Surprising, but true! The reindeer is the only deer species where both males and females have antlers. In December, male reindeer's antlers fall off and are replaced in the spring; meanwhile female reindeer keep their antlers all year long until they breed and deliver. So if Santa wants reindeer with antlers to lead his sled, he must choose females.

In fact, reindeer groups are usually led by females, especially during migration season. Reindeer ladies even have much thicker fat than reindeer gentlemen during winter, making them more suitable to take up an outdoor job on Christmas Eve. Altogether, Santa is more likely to prefer females when hiring reindeer for his sled team!

Researchers from the University of Lund using infrared cameras have found that "Rudolph" does in fact have a red nose. A reindeer's nose keeps a higher temperature than most of its other body parts. This helps the reindeer find food in deep snow.

The Taimyr herd of migrating Siberian tundra reindeer in Russia is the largest wild reindeer herd in the world, varying between 400,000 and 1,000,000.

Despite their seemingly large number, reindeer are classified in the "vulnerable" category by the International Union for Conservation of Nature. Over the last 25 years, the world's reindeer population has decreased by 40 percent. This global decline is linked to climate change and habitat disturbance. In November 2016, it was reported that more than 81,000 reindeer in Russia had died as a result of climate change. Longer autumns, leading to increased amounts of freezing rain, created a several inches of ice over lichen, starving many reindeer.

In Santa's home country Finland, the reindeer population is also dropping drastically. If climate change goes on, Rudolph's kind may be increasingly threatened.

There are reindeer living in the Greater Xing'an mountain range of northeast China. The Aoluguya, a tribe of the Ewenki ethnic group in north China's Inner Mongolia Autonomous Region, is the only tribe that still breeds reindeer in China.

CGTN Nature's film crew are now visiting the Greater Xing'an Range nature reserve. Here is a trailer for their new documentary:

(Video provided by CGTN Nature's film crew. Edited by An Qi)

(If you want to contribute and have specific expertise, please contact us at nature@cgtn.com.)