1. Their antlers are velvety fingerprints.

Reindeer in Yamal Peninsula. 09/30/2009 © Greenpeace / Steve Morgan

Reindeer antlers are bony appendages that grow every year. The antlers grow quickly – up to 2 cm per day – in a blood-supply-rich material called "velvet", which is exactly what it looks like. That's why antlers feel warm as they are growing. Reindeer are the only mammals that grow new sets of antlers annually. Like human fingerprints, no two antlers are the same – every antler has its own shape and design.

2. Their name means "snow shoveller".

A Svalbard reindeer (Rangifer tarandus platyrhynchus) grazes in wintry conditions in Adventdalen, Svalbard. 03/07/2014 © Larissa Beumer / Greenpeace

Reindeer and caribou are two names for the same species (Rangifer tarandus), with 'reindeer' generally referring to the domesticated variety that are herded by humans and pull sleds. The name caribou originates from the Mi'kmaq word Qalipu (pronounced hal-lay-boo) which means "snow shoveller". This is a reference to the shovel-like design of the sharp edges of their concave hooves that are used for digging in the snow for lichen and other plants.

3. They have magical eyes that change colour.

Reindeer at Lake Inari in North Finland. 02/15/2006 © Markus Mauthe / Greenpeace

Reindeer are the only mammals whose eyes are known to change colour depending on the season. Their eyes are gold during the summer when the reindeer experience almost constant sunlight, but in the darkness of winter their retinas become less reflective and their eyes appear blue.

4. Reindeer calves are faster than an Olympic runner.

Winter forest at Lake Inari in North Finland. Reindeer calf. 02/15/2006 © Markus Mauthe / Greenpeace

A one-day-old North American reindeer can outrun an Olympic sprinter. Adults can run at speeds of 40-50 mph. This is why reindeer are not hunted by polar bears – the bears would overheat while chasing a reindeer!

5. Santa's crew is all female.

© Creative Commons

Male reindeer shed their antlers at the end of the mating season in early December. Females, however, keep their thinner antlers throughout the winter. If all the sightings are to be believed, then it's the women who pull Santa's sleigh full of presents through the sky.

6. They communicate with their knees.

Svalbard reindeer (Rangifer tarandus platyrhynchus) graze in wintry conditions in Adventdalen, Svalbard. 05/09/2014 © Jon Lorentzen / Greenpeace

Some reindeer subspecies have knees that make a clicking noise as they walk so they can stay together in a blizzard. They also vocalise: scientists have found that males have a large air sac in their neck that enables them to emit a hoarse rattling sound, or mating call. The throaty call could deter rival males while attracting a potential mate. In the females, air sacs allow moms to individualise their calls when communicating with their young. Each reindeer makes a unique call.

7. They're energy efficient.

Svalbard reindeer (Rangifer tarandus platyrhynchus) graze in wintry conditions in Adventdalen, Svalbard. 03/07/2014 © Elise Biersma / Greenpeace

Reindeer are able to outperform all other land animals in their energy efficiency. They were built for the snow and cold, with hollow hair that traps air and keeps them well-insulated. During the winter a reindeer's facial hair grows very long down to the lips, which helps to protect the muzzle when they graze in snow. Their noses are specially designed to warm the air before it gets to their lungs. In extremely cold weather reindeer are able to lower the temperature in their legs to just above freezing, which helps them to avoid losing body heat.

8. They have fancy feet.

© Creative Commons

Like their eyes, a reindeer's feet can change from season to season. In the summer, their footpads become sponge-like to give them extra traction in the soft tundra. In the winter, the pads shrink and tighten, exposing the hoof rim, which cuts into the ice and snow and allows them to dig for food.

9. Their antlers are delicious?

© Creative Commons

When reindeer shed their antlers every year, they don't just lie on the ground. Instead the antlers are eaten by rodents and other animals, and are a great source of calcium and minerals.

10. They have super-intense milk.

Winter forest at Lake Inari in North Finland. Reindeer with calf in the snow. 02/15/2006 © Markus Mauthe / Greenpeace

Reindeer milk is said to be some of the richest and most nutritious milk produced by any terrestrial mammal. It has an impressive 22% butterfat and 10% protein. In comparison, cow's milk has only 3 to 4% butterfat.

Trillia Fidei-Bagwell is the international online campaigns co-ordinator for Greenpeace’s Arctic campaign, and works with Greenpeace Argentina.