Reindeer chew to sleep less. This is important during arctic summer days

Traditionally, reindeer are Santa’s helpers and pull his sleigh filled with gifts. Visiting all corners of the world in one night is an activity that requires excellent organization and often also divided attention. As research published in the magazine “Current Biology” shows, these animals can boast of impressive multitasking even beyond Christmas Eve.

The daily cycle above the Arctic Circle is disturbed in winter and summer, when nights or days last up to 24 hours a day. To check the effect of changes in the amount of light on the sleep of European reindeer (Rangifer tarandus tarandus), scientists used non-invasive electroencephalography (EEG). Observations were carried out for several days around the autumn equinox, winter solstice and spring equinox. The animals were housed in indoor stables with controlled lighting, unlimited food and constant temperature.

Researchers observed that ruminants slept about the same amount in summer, winter and autumn, although in other species the amount of sleep usually changes with environmental conditions. Regardless of the season, the reindeer spent an average of 5.4 hours each day in sleep outside the REM phase (i.e. in NREM phases), 0.9 hours in the REM phase and almost 3 hours chewing digested food.

EEG readings from reindeer chewing food showed the presence of waves and spikes characteristic of deep NREM sleep. The sleeping and chewing reindeer showed similar behavior: they stood or lay quietly and reacted less to what was happening around them. The researchers also deprived the reindeer of sleep for two hours to see if rumination could reduce their need for sleep. The readings then showed increased theta wave activity, which indicates an increase in sleep pressure and is a sign of increasing fatigue. However, when the reindeer chewed their food for a while, theta wave activity decreased during subsequent sleep.

“This means that reindeer do not have to sacrifice sleep as they spend more time ruminating,” explained Melanie Furrer from the University of Zurich, the study’s lead author.

Previous research has shown that Arctic reindeer do not exhibit circadian behavioral rhythms across seasons, but are more active during the day during the spring and autumn equinoxes, when light-dark cycles occur. According to scientists, the ability to “sleep while chewing” is especially important in the summer, when food is plentiful in the Arctic and reindeer eat almost constantly.

“Chewing increases nutrient absorption, so it is important that reindeer spend enough time doing this in the summer to gain weight in anticipation of winter,” Furrer added.

In further research, the authors want to compare the impact of rumination during sleep and wakefulness on reindeer. Scientists also plan to look at young individuals. As Furrer explained, the need for sleep is much higher in small children and infants than in adults, so researchers are interested in looking at sleep processes in younger ruminants.