Do dolphins and whales sleep
There can be no doubt that whales do sleep like all mammals, birds, reptiles and so on, but nobody has ever seen a sleeping whale. It is extremely difficult to study the habits of such large animals. However, it has been possible to study dolphins in captivity.
It appears that these animals have the same body rhythm as we do. They sleep at night and are active during the day- though they may take the occasional nap.
How do whales and dolphins sleep ?
In calm water a dolphin sleeps as it floats on the surface. It sinks about one foot below the surface and every 30 seconds a quick flick of its tail brings it back to the surface again. Its one nostril, or blow-hole, situated on the top of its head, opens and takes in air. This toing and froing goes on automatically as the animal sleeps. It gives a slight movement of the eyelids which half-open each time it rises to the surface.
When the water is rough the dolphin re-surfaces more often (about every 15 seconds) and this time with a stronger flick of the tail.