Reindeer have a unique ability to sleep and eat at the same time, according to a study published in Current Biology. While they graze in the summer, the animals are able to sleep and ruminate simultaneously, saving time during the short Arctic season. Researchers monitored the brain activity of reindeer and found that when they were ruminating, their brain waves resembled those of non-Rapid Eye Movement sleep. The animals also showed behaviors associated with sleep, such as not reacting to disturbances. This adaptation allows reindeer to sleep consistently throughout the year and suggests that sleep during rumination serves a purpose in recovering brain functions.
https://www.smithsonianmag.com/science-nature/reindeer-sleep-and-eat-simultaneously-saving-precious-time-in-the-short-arctic-summer-180983495/