How Reindeer Keep Their Cool

Reindeer are made for frigid Arctic winters. But unlike humans, who can shed clothing when heat strikes, they can’t remove layers. Yet reindeer don’t burn up when running from predators in deep snow.

To figure out how the mammals chill out, scientists trained nine female reindeer (less temperamental than males) to run on a treadmill. They then observed their reactions as they heated up, finding that the animals rely on a three-pronged approach to keep their cool.

First, they pant, close-mouthed. If their temperature continues to climb, they stick out their tongues to evaporate saliva and cool the blood. “Only in extreme conditions”—when brain temperature hits 102 degrees—“do they activate the third stage of defense,” says Arnoldus Schytte Blix of Norway’s University of Tromsø, who published the findings in The Journal of Experimental Biology.

The trick: “Cold blood from the nose selectively cools warm blood en route to the brain,” a heat transfer that prevents a possibly life-threatening two-degree rise in brain temperature. No doubt about it—reindeer stay cool under pressure.

This story originally ran in the November-December 2012 issue as "Chill Out."