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Clever Trick: Reindeer Sleep Whilst Eating

Scientists discover that reindeer are able to ruminate and sleep at the same time.

Santa’s reindeer spend the offseason resting up, getting ready for the gruelling feat of circumnavigating the globe in a single night. But the demanding Arctic winter means that their non-flying relatives must also prepare diligently for the season.

Reindeer standing in deep snow

Reindeer graze incessantly during the short northern summer, storing up fat reserves for the cold, dark months when both sunlight and food will be in extremely short supply. Reindeer spend so much of the summer eating that it would appear they have little time for anything else - including sleeping.

Neuroscientist Melanie Furrer of the University of Zurich and colleagues suspected that reindeer might simply sleep less during the short season, and then catch up on their Zs by slumbering away during the winter. “But that’s not what we found,” she says. Instead, reindeer sleep the same amount throughout the whole year, even when they have to focus on eating in warm months. “We found that they have a strategy to deal with it, being able to ruminate and sleep at the same time, to save time in the summer.”

The study also found that the more time reindeer spent ruminating, the more rested they were. EEG brainwave recordings revealed the reason why: When the reindeer are ruminating, their brain waves resemble those during non-rapid eye movement (REM) sleep. Because they seem to enjoy the benefits of such sleep while serenely chewing their cud, the animals are rested after ruminating.

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