Chewing it over: How reindeer rest after a big night

Reindeer probably feel more rested after ruminating, according to the first study recording the animal’s brain patterns using electroencephalography (EEG). 

Swiss and Norwegian scientists recorded reindeer brainwaves, behaviour, and sleep finding the animals’ brain patterns and behaviour while chewing cud resembles their non-rapid eye movement (REM) sleep.

Publishing in Current Biology, the scientists used non-invasive EEG on 4 adult female Eurasian tundra reindeer (Rangifer tarandus tarandus) in Tromsø, Norway during the autumn equinox, summer solstice, and winter solstice. In each season, recordings lasted 4 days.

Reindeer credit leo rescia
Reindeer / Credit: Leo Rescia

They found reindeer slept similar amounts during winter, summer and autumn despite the absence of light-dark cycles in the Arctic during winter and summer, and extreme seasonal variations in activity and food intake.

Regardless of season, the animals spent an average of 5 hours 24 minutes in non-REM sleep, 54 minutes in REM sleep and 2 hours 54 minutes ruminating each day.

They also found when reindeer spent less time in non-REM sleep (due to disturbance), they spent more time ruminating.

The authors suggest resting while ruminating might enable reindeer to feed more during summer in preparation for arctic winter.

As well as comparable brainwave patterns during non-REM sleep and while ruminating the animals’ behaviour was also similar, reindeer sitting or standing quietly. 

Their findings suggest reindeer have weaker circadian systems than other animals, like the Arabian oryx (Oryx leucoryx) which decreases sleep during summer.

Screenshot of reindeer surveillance 4 credit current biology furrer et al
Reindeer with EEG / Credit: Current Biology Furrer et al

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