Dolphins sleep using a unique method called unihemispheric slow wave sleep (USWS), where only one half of their brain sleeps at a time while the other half remains awake. This adaptation allows them to rest without losing consciousness, which is crucial because dolphins are conscious breathers-they must actively decide to come to the surface to breathe and cannot afford to be fully unconscious lest they drown
. During this sleep, the half of the brain that is awake controls breathing and monitors the environment for predators or obstacles. Dolphins often close the eye opposite the sleeping brain hemisphere, so one eye remains open to stay alert
. They may rest motionless at the water's surface, breathing regularly, or swim slowly near the surface while sleeping
. Dolphins typically alternate which brain hemisphere sleeps every couple of hours, allowing both sides to get rest throughout the day and night. Studies show dolphins spend about a third of their day sleeping in this way
. Their breathing rate slows down during sleep, from about 8–12 breaths per minute when awake to 3–7 breaths per minute while resting
. This sleep strategy helps dolphins maintain vital functions like breathing and vigilance in their aquatic environment, ensuring they can surface for air and stay safe from threats while still getting the rest they need
