A good night's sleep!

I awoke this morning to find NO CHILDREN at all in my bed.  A very rare event indeed.  I can't remember the last time that happened but I am certainly not complaining.  It was lovely to have a full night's sleep with no interruptions for a change.  I was perfectly happy to have little Rohan crawl into bed beside me at the reasonable hour of 7 am for a cuddle.  Turns out it wasn't Rohan but a "baby Dolphin" and I was the "Mammy Dolphin" and the bed was actually the sea.  It did not take long for Rohan's clever little mind to start to wonder....
......................... "HOW DO DOLPHINS SLEEP IN THE SEA, MAMMY?"

Bottlenose dolphin; Photo credit:  Stuart Westmorland/Corbis

SO, HOW DO DOLPHINS SLEEP?

Dolphins (and whales) are mammals just like us, they need to breathe in air.  Unlike us, dolphins have adapted their bodies breathing system (respiratory system) to be able to go long periods between breaths.  This allows them to stay under water for up to 30 minutes at a time before they need to surface and take the next breath.  The other difference between dolphins and other land mammals is that we breathe involuntarily (without thinking about it) while they make a conscious decision to take a breath.

HOW CAN DOLPHINS SLEEP IF THEY NEED TO STAY CONSCIOUS TO BREATHE?

Dolphins have overcome the problem of having to stay conscious to breath by only shutting down one half of their brains at a time while sleeping.  This process is called unihemispheric sleep and basically means that one half of the brain sleeps while the other half stays awake and alert.  Interestingly, one eye stays open while the dolphin sleeps, it is the eye on the opposite side to the sleeping brain.  This allows the dolphin to stay alert to its environment at all times, a requirement necessary for its survival.

Scientist determined unihemispheric sleep in dolphins by monitoring brain activity in captive dolphins using a process called electroencephalography.  This process involves attaching electrodes to the dolphins head and tracking brain wave activity as electrical pulses. Such research suggests that dolphins are in this sleep state for approximately eight hours a day.

Studies into the unihemispheric sleep patterns of some mammals suggest hopeful correlations and potential solutions to human sleep disorders such as narcolepsy.


WHERE DO DOLPHINS SLEEP?

There is no real reason why dolphins can't sleep anywhere within the ocean, but, given that they need to surface fairly frequently to breathe, it is most likely that they sleep just below the surface.


DO ANY OTHER ANIMALS SLEEP LIKE THIS?

Mammals, other than dolphins, that use unihemispheric sleep include whales, porpoises, manatees, sea lions and seals.

This types of sleeping has been observed in some birds and is suggested as a probable form of "sleeping on the wing" for migrating birds.









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