Whales sleep for only a short time, while also in a vertical position with one of their brains shut off. This means that one half of their brain is awake while the other half is asleep. This process is called unihemispheric slow-wave sleep (USWS).
USWS in Whales
Whales need to stay conscious while sleeping to swim and breathe, as they’re conscious breathers, unlike humans. They must always control their breathing, making deep sleep dangerous. Therefore, USWS is an ideal solution for whales to avoid drowning.
How Long Do Whales Sleep?
Whales sleep an average of 7.1% of the day, about 25 minutes, the least of any mammal. When they sleep vertically, this record holds. However, their sleep can last longer if they sleep horizontally. This happens as whales use USWS during low-level activities.
Why Do Whales Sleep Vertically?
There’s no clear reason why whales sleep vertically. Some experts think it helps them stay conscious and aware of their surroundings. It might also keep them close to the surface for breathing, or it could be just a preference.
