SATURDAY, Dec. 24 (HealthDay News) -- Reindeer have lots to do this time of year -- from playing their reindeer games to dragging heavy sleighs -- but despite all their frenzied activity they manage to keep cool under luxurious winter coats without getting dangerously overheated, researchers have found.

Now, Norwegian scientists have gained insight into how they do it by monitoring the brains of reindeer as they exercised on solid ground.

In the study, the reindeer trotted at speeds of 6 miles per hour on a treadmill in temperatures from 50 to 86 degrees Fahrenheit.

"Reindeer are the best animals to work with; once they trust the trainer they will do anything for you," study author Arnoldus Blix, a biologist at the University of Tromso, said in a news release from The Company of Biologists.

Blix and colleagues found that reindeer pant with their mouths either closed or open, allowing them to evaporate water from either the nose or the tongue. Evaporating water helps the reindeer to cool blood in their nasal sinuses; the cooled blood then goes back to the rest of their bodies.

The researchers also discovered that the reindeer turn to another strategy when their temperatures get too high: they cool their brains through a heat-exchange system. They do this by diverting the blood that had been cooled by going through the nose to the brain and away from the body. This protects the brain from overheating.

The findings were published in a recent issue of the Journal of Experimental Biology.

Reindeer are unique in other ways. For one, they've lost almost all signs of the circadian clocks that humans and other animals have because the day/night cycle at Arctic latitudes is so irregular.

Reindeer are also extremely energy-efficient animals, a fact that allows them to travel great distances -- more than 3,100 miles a year, at least in American herds.

And, of course, they're able to fly around the world every Christmas Eve, although they appear to get a big boost from the powers of imagination.

More information

Learn more about reindeer from the Smithsonian National Museum of Natural History.