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Reindeer catch up on sleep when you would least expect it

SCOTT SIMON, HOST:

Of course, it's almost Christmas Eve, the night when Santa and Rudolph pull the all-nighter to deliver their gifts. But what about the rest of the year? How do reindeer manage to get enough sleep? A group of scientists say their secret might lie (laughter) in multitasking. You can only hear this story here. Here's NPR's Ari Daniel.

ARI DANIEL, BYLINE: Did you plan to have this story come out around Christmas (laughter)?

GABI WAGNER: Yes, a little bit (laughter).

DANIEL: Gabi Wagner is a neuroscientist at the Norwegian Institute of Bioeconomy Research. She says reindeer habitat is different from most places on the planet.

WAGNER: In winter and in summer in the Arctic, we either have constant darkness or constant light.

DANIEL: In summer, it's like an open buffet for the reindeer - lichens, herbs, mushrooms, plants - they're all available.

WAGNER: We know they're very, very active during the very short growing season in summer, and they're very lazy in winter when there isn't any food.

DANIEL: But during that summer feeding bonanza, when reindeer have so much eating to do and so little time to do it, when is it that they sleep? And do they sleep less than in the lazy winter?

MELANIE FURRER: To really know that, we need to measure brain activity.

WAGNER: Melanie Furrer is a neuroscientist at the University of Zurich, and she says that no one had ever studied a sleeping reindeer brain before. So she and her colleagues turned to several females that live in an enclosure in Tromso in northern Norway.

FURRER: Our data was recorded noninvasively - meaning that the electrodes were placed on their skin and not implanted in their brain.

DANIEL: She measured the reindeer's brainwaves continuously for several days straight in the summer, then again in the fall and once again in the winter.

FURRER: What we found was, first of all, they sleep a similar amount of time across the whole year.

DANIEL: Suggesting that even though reindeer spend all that time eating and moving around during the summer, they found a way to still get as much sleep as they do at other times of the year. But how? Furrer thought maybe something was happening during rumination when they were chewing their cud.

FURRER: While they chew, they are in a body position that is very similar to the one of deep sleep. So they have, usually, their eyes closed, and they are quite still.

DANIEL: Furrer looked at the brainwaves of the reindeer as they ruminated, and sure enough, they resembled those of deep sleep. In fact, the more the reindeer ruminated, the less deep sleep they required. Gabi Wagner says the conclusion is that rumination in reindeer serves two purposes - digestion and sleep. They're multitasking.

WAGNER: Not only does it help them to get the most energy out of the food they have, but it also makes sure that their brain gets enough rest, and they get the sleep they need. They're like us. They can't sleep one hour today and then catch up next week.

DANIEL: Rather, reindeer need a certain amount of sleep every day. The research appears in the journal Current Biology.

MENNO GERKEMA: Yeah, I think it's a fascinating study. I loved it.

DANIEL: Menno Gerkema is a retired chronobiologist from the University of Groningen in the Netherlands who wasn't involved in the research.

GERKEMA: I'm rather enthusiastic about all the suggestions that are hidden in this paper, suggestions for further research for looking at other animals.

DANIEL: As scientists look to what's next, these new findings also echo the traditional wisdom of the Sami. Gabi Wagner works with these Indigenous people of Norway who've herded reindeer for centuries.

WAGNER: Sami reindeer herders have known all along that the animals need peace to eat and lie down to ruminate.

DANIEL: Wagner says it's an important part of their biology that should be considered when setting aside rangeland for the animals - to give reindeer the space to chew their cud and sleep deeply, including on those long summer days when Christmas is but a dream. Ari Daniel, NPR News. Transcript provided by NPR, Copyright NPR.

NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.

Ari Daniel is a reporter for NPR's Science desk where he covers global health and development.