Dolphins Are Half Awake When Sleeping
When dolphins sleep, they often rest motionless at the top of the water. Hence, dolphins sleep in a very different way from humans. When we sleep, we have prolonged periods of unconscious sleep and are usually unaware of our surroundings. We have a breathing reflex that allows us to breathe automatically even when we are asleep.
However, dolphins cannot sleep in this way. They have to remain conscious as they sleep because dolphins cannot breathe automatically. Dolphins have to decide when to breathe actively. To get around this, dolphins only allow one half of their brain to sleep while the other half stays awake to enable the dolphin to breathe.