Dolphins are fast, playful, and intelligent animals, but where do they sleep? In this article we’ll explore the answer to that question and see how these amazing mammals get their rest!
Dolphins and whales do not find caves or other places to rest like humans, so they have developed a unique way of sleeping. They enter a state of sleep called unihemispheric slow wave sleep, or USWS for short. During this time only one half of the brain (and the opposite eye) sleeps while the other remains at a low level of alertness, ready to watch for predators or obstacles, and signal when it’s time to rise to the surface for air. This allows dolphins to be able to breathe automatically while still being conscious enough to react to danger, and remain aware of their environment so they can surface when necessary.
When a dolphin is in a state of USWS they will typically lie motionless at the water’s surface or swim slowly close to it, but will wake up frequently to breathe. This makes them look a bit like they are sleep walking! Newborn dolphin and whale calves do not enter this state of sleep for the first couple of weeks of life.
In captivity, humpback whales have been observed to lie motionless at the ocean’s surface for around 30 minutes, however they cannot rest for much longer or risk losing too much body heat from being inactive. It is also believed that dolphins may sleep in groups, either lying at the surface with their blowhole exposed or drifting slowly together.