Rudolph and the Other Reindeer Have a Gift for Multitasking, Study Finds

Some people, as the phrase goes, are so bad at multitasking that they "can't even walk and chew gum at the same time."

The same cannot be said of reindeer, however, with a new study suggesting that Rudolph and his ilk might be able to sleep and chew cud simultaneously.

To be precise, researchers from Norway and Switzerland found that the brain waves seen in reindeer while ruminating—re-chewing partially digested food to help absorb more nutrients—often resemble those seen during non-REM sleep.

Non-REM, in which rapid eye movements (REM) are not exhibited, are the stages of sleep during which the brain organizes memories, repairs injuries and allows one to wake feeling rested.

The team believes that reindeer may multitask this way to get extra rest during the summer months without having to sleep longer hours.

This could be essential for the animals, which feed almost non-stop at this time of year in preparation for the long and food-scarce Arctic winter.

The study was undertaken by neuroscientist Melanie Furrer of the University of Zurich and her colleagues.

"The more reindeer ruminate, the less additional non-REM sleep they need," Furrer said in a statement. "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."

At this time of year in the Arctic, the sun can always be seen above the horizon. In contrast, in winter, the Arctic experiences a permanent night.

In fact, previous studies have found that during these seasons, when light–dark cycles are absent, Arctic-dwelling reindeer do not display the usual behavioral rhythms of being more active during the day, as they do at other times of year.

However, it had previously been unclear whether these differences in the seasons also had an effect on how much—and how well—the animals sleep.

In the new study, the team measured the brain activity of four Eurasian tundra reindeer on three occasions: at the autumn equinox, on the summer solstice, and at the winter solstice.

The animals, all of which were adult females, belong to a captive herd kept at the University of Tromsø–The Arctic University of Norway.

All of the experiments were undertaken indoor stables, with the reindeer given access to unlimited food and kept under controlled lighting and at a constant temperature.

Even though the reindeer were considerably more active during the summer, the researchers found that the reindeer slept around the same amount during summer, autumn and winter—meaning that their sleep requirements are tightly regulated by the brain, and not by their environment.

This, paper author Gabi Wagner of the Norwegian Institute of Bioeconomy Research in Oslo explains, stands in contrast to various other species that change the amount that they sleep in response to environmental conditions.

According to a 2018 study, she told Newsweek, "Arabian oryx sleep almost double as much in winter (6.7 hours) than in summer (3.8 hours)."

Other examples, she added, include fur seals, who suppress REM sleep when forced to slumber in water; male pectoral sandpipers, who sleep just one hour a day during the breeding season; and great frigatebirds, who sleep while flying, but count down on the duration of this when in the air.

On average, the team noted, the reindeer spent 5.4 hours in non-REM sleep and 0.9 hours in REM sleep each day, regardless of the season—as well as roughly 2.9 hours ruminating.

"The fact that reindeer sleep the same amount during this winter and summer implies that they must have other strategies to cope with limited sleep time during the Arctic summer," Furrer said.

When both sleeping and ruminating, the team found the reindeer exhibited similar patterns of behavior, tending to either quietly sit or stand, and reacting less to disturbances like their neighbors sitting down or getting up.

In fact, the animals responded to such stimuli only 25 percent of the time when ruminating and 5 percent of the time when in non-REM sleep, compared with 45 percent of the time when fully awake.

While ruminating, the animals were also found to often keep their eyes closed, like they typically do while sleeping.

And when chewing the cud, the reindeer's brain activity readers were frequently seen to resemble those seen with non-REM sleep—including an increase in so-called slow-wave activity.

This activity, the researchers explain, is indicative of a build-up of "sleep pressure," the unconscious biological drive for more and deeper sleep.

It is not completely clear if the reindeer were fully asleep while ruminating, or just in a sleep-like state, Wagner notes—but the former seems likely, based on their brain activity.

She adds: "This is also in agreement with recent studies in other ruminants such as sheep, using a more invasive technique—electrodes embedded in the brain."

Scientists have previously determined that other ruminant animals—domestic sheep, goats, cattle, and lesser mouse-deer—also produce sleep-like brain waves while chewing the cud, but it had not been clear whether this process also served a sleep-like restorative function.

To explore this with the reindeer, the team experimented by depriving the animals of sleep for two hours using a combination of food and attention, and measured their brain waves when sleeping both before and after this interference.

Brain scans revealed that the reindeer experienced more slow-wave activity after sleep deprivation, indicating a build-up of sleep pressure and suggesting they were having a deeper sleep.

However, the more the reindeer ruminated after being kept awake and before sleeping, the less slow-wave activity when they slumbered, the team found,

"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," Furrer explained.

The reindeer may not sleep all the time when ruminating, Wagner explains, because like us they probably need the right conditions to drift off, without noise, distraction, or fear.

"It is very important for reindeer that they get enough undisturbed time to ruminate," she says.

Oleg Lyamin, who was not involved in the present study, is a researcher with the University of California, Los Angeles who has conducted research into sleep in another ungulate, or "hoofed mammal", the lesser mouse-deer.

"Rumination during non-REM sleep has been recorded in domesticated ungulates and in the lesser mouse-deer," he told Newsweek. "From my position, it is not unusual that reindeer experience rumination during non-REM sleep."

"The link between sleep and rumination is a big puzzle for researchers," animal behavior expert professor Katy Proudfoot of the Sir James Dunn Animal Welfare Centre in Charlottetown, Canada, told Newsweek.

The problem, she explained, is that "the process of ruminating—chewing, swallowing, regurgitating and re-chewing food—interferes with our ability to measure sleep using electrophysiology."

Furrer and her colleagues have neatly overcome this issue by filtering the data and testing arousal levels during rumination, reaching the conclusion that reindeer likely sleep during rumination, Professor Emma Ternman, an animal scientist from Norway's Nord University, told Newsweek.

She added: "This is a solid puzzle piece in the ruminant sleep research—the next step would be to quantify sleep during rumination."

As the reindeer appear to only enter a sleep-like state while ruminating some of the time, future studies should also compare the impact of different ruminating behaviors, the team said.

Ideally, they added, the reindeer would be studied in more natural, outdoor conditions.

However, this would likely require surgically implanted brain activity sensors, as opposed to the non-invasive, skin-attached electrodes used in the present study.

"We know sleep need is much higher in young children and babies compared to adults," Furrer said. "So it would be interesting to look at sleep in young reindeer."

"We think that this research might trigger more studies investigating sleep during rumination in reindeer and other ruminants," Wagner said. "Furthermore, it shows how important it is that reindeer have enough time for undisturbed rumination, as it is important for both digestive and sleep needs.

"Therefore, we hope that future research and political decisions on human activities in reindeer/caribou rangelands will take into account that reindeer have enough time and space for undisturbed rest."

Proudfoot concluded: "Understanding sleep in a variety of wild and domesticated species can give us insight into how sleep evolved, as well as help us better meet the needs of these animals when they are under our care."

The full findings of the study were published in the journal Current Biology.