Prancing around in fluffy fur coats, reindeer stay plenty warm when temperatures plummet below -50°C, but they can't exactly unzip to cool off after
exercise. To study how reindeer avoid overheating, researchers rounded up nine of the friendliest animals they could find and implanted probes into
major blood vessels in their heads that measured blood flow and brain temperature. Then they let the reindeer run on a specially designed treadmill. At
first the reindeer breathed through their noses, allowing the Arctic air to cool the blood in their sinuses before sending it on to the rest of the
body. But once they started breathing faster, up to 260 breaths per minute, they opened their mouths and panted like dogs, letting the air flow over
their big tongues to cool that blood. When their brain temperature reached a critical limit of 39°C, researchers report today in December issue of The Journal of Experimental Biology, the reindeer switched the blood flow pattern in their noses so that the coolest blood
would go to their heads and cool the brain, a strategy similar to their very distant relative: the African antelope.
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