Ruminating Reindeer Optimize Sleep Patterns, Finds Research

Reindeer chew the cud in their sleep, reveals new research.

The study shows that the more time Santa’s multi-tasking sleigh pullers spend ruminating, the less time they spend in non-rapid eye movement (non-REM) sleep.

EEG recordings of brain activity revealed that reindeer’s brainwaves during rumination resemble those present during non-REM sleep.

“The brainwave patterns suggest that the reindeer are more “rested” after lots of cud-chewing as they sleep,” said scientists.

They believe that this multitasking might help reindeer get enough sleep during the summer months when food is plentiful and reindeer feed almost 24/7 in preparation for the long and food-sparse arctic winter.

 “The more reindeer ruminate, the less additional non-REM sleep they need,” said study first author Melanie Furrer.

“We think it’s very important that they are able to save time and cover their sleep and digestive needs at the same time, especially during the summer months.”

Light-dark cycles are absent in the Arctic during winter and summer, and previous studies showed that Arctic-dwelling reindeer don’t display circadian behavioral rhythms during these seasons.

They tend to be more active during the daytime during the spring and autumn equinox when light-dark cycles are present.

However, it wasn’t known whether the seasonal differences also impacted how much – and how well – reindeer sleep.

The research team performed EEGs on Eurasian tundra reindeer in Tromsø, Norway, during the autumn equinox, summer solstice, and winter solstice.

The reindeer, who were all adult females, were part of a captive herd at UiT The Arctic University of Norway in Tromsø, and the experiments were conducted in indoor stables with controlled lighting, unlimited food, and constant temperature.

The findings, published in the journal Current Biology, found that reindeer slept around the same amount during winter, summer, and autumn, despite the fact that they were much more active during the summer.

That behavior is in contrast to other species that change the amount they sleep in response to environmental conditions.

On average, the reindeer spent 5.4 hours in non-REM sleep, 0.9 hours in REM sleep, and 2.9 hours ruminating during a given 24-hour period, regardless of season.

Neuroscientist and doctoral student Furrer, of the University of Zurich in Switzerland, said: “The fact that reindeer sleep the same amount during winter and summer implies that they must have other strategies to cope with limited sleep time during the arctic summer.”

She said one possible way is the opportunity for rest during rumination – the re-chewing of partially digested food, which is an important component of digestion for reindeer and other ruminants.

Domestic sheep, goats, cattle, and Lesser mouse-deer have all been previously observed to produce sleep-like brain waves during rumination, but it was unclear whether rumination could serve a similar restorative function to sleep.

The research team found that the reindeer’s EEG readings during rumination resembled brainwave patterns that are indicative of non-REM sleep including increased slow-wave activity and sleep spindles.

Sleeping and ruminating reindeer also displayed similar behavior, tending to quietly sit or stand during both activities and were less reactive to disturbances such as a neighboring reindeer sitting down or getting up.

Reindeer directly responded to the disturbances – by looking toward the neighboring reindeer – 45 percent of the time if they were awake, but only 25 percent of the time if they were ruminating, and five percent of the time if they were in non-REM sleep.

The researchers then tested whether rumination could reduce the reindeer’s drive to sleep by depriving them of sleep for two hours and measuring their brain waves during sleep before and after the deprivation.

Following sleep deprivation, the reindeer’s EEG readings showed increased slow-wave activity, which is indicative of a build-up of “sleep pressure” – the unconscious biological drive for more and deeper sleep -suggesting that reindeer experience deeper sleep following sleep deprivation.

However, when the reindeer ruminated, the slow-wave activity was decreased during subsequent sleep, and the more they ruminated, the more the slow-wave activity decreased.

Furrer said: “This suggests that rumination reduces sleep pressure, which could benefit the reindeer because it means they don’t have to compromise on sleep recovery when they spend more time ruminating.”

She says it is especially important during the summer because the more they eat, the more time the reindeer need to spend ruminating.

Furrer said: “Rumination increases nutrient absorption, so it’s crucial for reindeer to spend enough time ruminating during the summer in order to gain weight in anticipation of winter.”

She added: “We know sleep need is much higher in young children and babies compared to adults, so it would be interesting to look at sleep in younger reindeer.”

Produced in association with SWNS Talker