Does dolphins sleep??

Dolphins, like humans, are mammals. They are warm-blooded, bear live young, breathe air, and they require sleep. However, for dolphins, sleeping and breathing at the same time can pose a bit of a problem. Humans are able to breathe during sleep as they live on land and can perform the task unconsciously. However, dolphins are aquatic mammals; they must actively make the decision to breathe and come up to the surface for air. Fortunately, as Bob Holmes notes in his May 1, 2009 article "'Brain-juggling' lets dolphins avoid sleep deprivation" published in NewScientist, nature has come up with a remarkable solution to the problem so that dolphins sleep without drowning.

How Do Dolphins Sleep?

The February 2, 1998 Scientific American article "How do whales and dolphins sleep without drowning" describes this interesting process of dolphin sleeping. Dolphins are able to send one half of their brain to sleep at a time so that they are never completely unconscious.The other half of the brain monitors what’s going on, ensuring that the animal stays out of danger and continues to breathe. Which half sleeps switches from nap to nap. Dolphins often swim with dolphins in groups called pods. During sleep they keep at least one eye open, allowing them to stay in contact with the others in the pod and coordinate their movements. Although they could likely sleep anywhere, usually dolphins sleep near the surface so that they can come up for air easily. These creatures can often be seen swimming slowly near the surface with little movement. This action is called “logging” and these dolphins are at rest.

Do Dolphins Have Dreams?

Perhaps dolphins dream about their day, eating, chatting with other dolphins, a round-the-world swim with dolphins in pods. The truth is nobody knows for sure. However, Margaret Klinowska does note in her September 26, 1994 essay “Brains, Behaviour and Intelligence in Cetaceans” published in the second edition of 11 Essays on Whales and Man, that dolphins are one of the few mammals that do not have REM sleep. Humans sleep during the REM stage of the sleep cycle. One could deduce that if dolphins don’t have a REM stage, then they can’t have dreams. However, some scientists dispute this claim and say dolphins merely have very low levels of REM sleep. It’s also possible that dolphins sleep and dream differently from humans. Studies done on captive belugas and grey whales show that these aquatic mammals sometimes have muscular spasms during their brief REM stage, which could be associated with dreaming.

How Do Scientists Know Dolphins Sleep?

Scientists don’t just swim with dolphins and watch them for hours, although observation is an important component of their studies. The 1998 Scientific American article describes how scientists use electroencephalography – hooking up electrodes to captive dolphins’ heads and measuring the electricity levels in their brains. The resulting data is an electroencephalogram or EEG. The EEG shows that during sleep, half of the dolphin’s brain is active while the other half shuts down. Studies show that dolphins sleep about eight hours a day.

by WEIJIE .