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Reindeer Can Sleep While They Chew


Aug 19, 2003
Sounds like Homer Simpson.

Reindeer can sleep while they chew​

Time spent chewing cud eases the reindeer’s need for sleep, a new study finds​

Two reindeer forage for food on the snowy ground.

Arctic reindeer make time for digesting by doing it in their sleep, a new study suggests.

By Laura Sanders DECEMBER 22, 2023 AT 11:00 AM

In this busy holiday season, many of us multitask. Arctic reindeer are no exception.

Reindeer can eat and sleep at the same time, a new study suggests. This timesaving strategy, described December 22 in Current Biology, adds to the number of ingenious ways animals can catch some z’s under tough conditions (SN: 11/30/23).

Arctic reindeer are quite busy in the summer — eating when the sun shines around the clock and the food is abundant. Like other ruminants, reindeer spend a considerable amount of time chewing on regurgitated food, making it smaller and easier to digest. Finding time to sleep amid all this cud chewing might be tough. But not if the reindeer could sleep while they chewed.

To find out if the reindeer could actually sleep-eat, neuroscientist Melanie Furrer and chronobiologist Sara Meier, along with their colleagues, trained four female Eurasian tundra reindeer (Rangifer tarandus tarandus) to tolerate a pen and electrodes on shaved patches of skin. The process involved some kicks and lots of lichen treats, “which is like candy to them,” says Meier, of the University of Zurich.

Four reindeer stand in pens eating food as researchers study them.

Reindeer were monitored with electrodes as they slept and ruminated, allowing researchers to study those states. M. FURRER ET AL/CURRENT BIOLOGY 2023

The researchers were looking for the brain waves that appear during non-REM sleep, a deep, restorative sleep phase. These waves appeared when the reindeer were chewing cud, though the chewing motion itself made it hard to say whether the signal was identical to that of a regular sleep session. “We couldn’t go into detail by looking only at the brain waves, because we have this chewing in there that disturbs it a bit,” says Furrer, also of the University of Zurich.

Still, other signs also pointed to sleep while chewing. The reindeer were calm while chewing, often with their eyes closed. “They were in a very relaxed state that resembles the body position of non-REM sleep,” Furrer says. Ruminating reindeer were also harder to disturb; rustling from neighboring reindeer was less likely to get a look from a ruminating reindeer. When reindeer are kept awake, they need catch-up recovery sleep. But time spent chewing decreased this time spent in recovery sleep, the researchers found.