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Why Rudolph's No Red-Eyed Reindeer

The animals don't get tired, study shows

WEDNESDAY, Dec. 21, 2005 (HealthDay News) -- A study released just in time for Santa's nocturnal sleigh ride suggests his reindeer, at least, won't be tired.

That's because the day/night cycle at Arctic latitudes is so irregular that reindeer have long ago disposed of all but the faintest of the circadian clocks that humans and other animals are saddled with, according to a Norwegian study.

The bottom line: "On his round-the-globe trip on Christmas Eve, Santa would have to work through his 'inner night,' while Rudolph would feel no such constraints," said lead researcher Karl-Arne Stokkan, a professor in the department of Arctic Biology at the University of Tromsø.

His team published its findings in the Dec. 22 issue of Nature.

According to Stokkan, most vertebrates on the planet have developed strict inner clocks timed to a 24-hour cycle that help the body anticipate and prepare for predictable changes, such as sunrise and sunset, or seasonal changes. As anyone who has encountered jet lag knows, humans who artificially sidestep these rhythms do so at their own peril.

But what about animals -- certain species of reindeer -- that spend their lives in Arctic climes, where a winter's night is endless and a summer's day is 24 hours long? At these high latitudes, days with a "usual" day/night division only occur during 18 weeks of the year, in the autumn and spring.

In their study, Stokkan's group equipped two species of reindeer with small "data loggers" that recorded their activity over a full year. They concentrated on "mountain" reindeer living on mainland Norway (latitude 70 degrees N), and Svalbard reindeer, living even farther north on the Svalbard archipelago (78 degrees N).

The researchers found the reindeer were "intermittently, continuously active around the clock," Stokkan said. "Only when they experience a day/night cycle in spring and autumn do they show a period of extended rest -- generally during the night."

But this transient, seasonal "rest period" was of short duration, and almost disappeared among the more northern Svalbard subspecies of reindeer, Stokkan added.

This type of high-latitude adaptation makes sense, he said, because adhering to a strict bio-clock "may actually be a burden" for creatures living in these climes.

In lieu of sunlight/darkness, reindeer activity may be directed by other biological influences, the Norwegian expert speculated. Because they are ruminant creatures, the life cycles of tiny intestinal microorganisms that aid in digestion probably play a role "as strong as that of the solar-day cycle, breaking [the reindeers'] activity into multiple, repetitive bouts of activity and inactivity," he said.

His team also detected similar activity patterns in an Arctic bird, the Svalbard ptarmigan, suggesting that a weakened circadian clock may be common to most animals that make the Arctic or Antarctic their permanent home.

Reindeer activity may also remain relatively stable once they are removed from the Arctic.

Brian Adelhardt, along with his wife Pat, tend a large number of reindeer at Applewood Farm, open to the public in Whiteford, Md.

"At our latitude, 39 degrees north, we really don't see any appreciable difference in our animal's activities between mid-summer and mid-winter," he said.

Stokkan stressed that his four-legged findings have implications for human activities, too.

When it comes to clock-related troubles in humans, such as jet lag, shift-work woes and the mid-winter "blahs," the reindeer research "shows that some animals may have alleviated similar problems by reducing the strength of their inner, biological clocks," he said.

Right now, though, not even Santa has figured how to do that.

More information

To learn more about Donner and Blitzen's kin, head to the University of Alaska Reindeer Research Program.

SOUCES: Karl-Arne Stokkan, Ph.D., professor, department of Arctic biology, University of Tromsø, Norway; Brian Adelhardt, co-owner, Applewood Farm, Whiteford, Md.; Dec. 22, 2005, Nature
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