Reindeer pant to lower their brain temperatures when running in fur coats, according to research.
Scientists in Norway trained reindeer to run on treadmills to study how they stayed cool under physical exertion.
The animals are heavily insulated against the cold of Arctic winters, leaving few methods of losing heat.
Results showed the reindeer inhaling large quantities of cold air and transferring heat by panting.
Professors Arnoldus Blix and Lars Folkow from the University of Tromso worked with Lars Walloe from the University of Oslo on the study.
Their findings are published in the Journal of Experimental Biology.
"Reindeer are the best animals to work with; once they trust the trainer they will do anything for you," Prof Blix told the journal.
After training the reindeer to run on the treadmill, the scientists measured their physiological responses to exercise in a cold environments.
In the early stages of running, the reindeer's breathing changed from seven breaths per minute to 250.
Blood flow to the face also increased and as the inhaled air passed over blood vessels inside the reindeer's noses, the temperature of this blood dropped.
This cooler blood then circulated around the body to cool the hard-working, heat-stressed muscles.
Subsequent panting then exposed the reindeer's large wet tongues to the cool air.
"They do not have sweat glands like us humans which would ruin the insulative properties of their fur, but make use of the same principle - heat dissipation through evaporation of water - when they pant," Prof Folklow told BBC Nature.
Finally, when their brain temperature reached a critically hot 39C, the reindeer switched to another strategy.
The team found that through "selective brain cooling", the reindeer diverted the cooled blood from their noses into their heads, where it reduced the temperature of blood circulating to the brain, protecting it from overheating.
"This high-arctic [animal] which tolerates cold very well, also has an immense capacity to tolerate heat stress due to the high efficiency of the panting mechanism and the habit of resorting to brain cooling when the heat load gets really high," said Prof Folklow.
Previous studies have highlighted this ability in sheep, leading scientists to question whether all species of hoofed mammal can selectively cool their brains.
By Ella Davies Reporter, BBC Nature
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