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.
Dolphins have captured
the hearts of many people. However, many species are endangered due to fishing
practices and human caused environmental changes. Hopefully, actions can still
be taken to save this wonderful species. They should be able to live in their
natural environments peacefully whether asleep or awake.
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