How do whales and dolphins sleep without drowning? : Scientific American

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Source: www.scientificamerican.com/article.cfm?id=how-do-whales-and-dolphin


how do dolphins sleep


How Do Dolphins Sleep?

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** How Do Dolphins Sleep? **

By Jennifer Kennedy, About.com Guide

"Bottlenose Dolphins / NOAA"

Bottlenose Dolphins (/Tursiops truncatus/)

NOAA
*Question: *How Do Dolphins Sleep?
Dolphins can't breathe underwater, and so every every time a dolphin needs
to breathe, it has to make the decision to come to the water surface to
breathe and supply its lungs with oxygen. Yet a dolphin might only be able
to hold its breath for about 15-17 minutes. So how do they sleep?
*Answer: *

Dolphins sleep by resting one half of their brain at a time. This is called
unihemispheric sleep. The brain waves of captive dolphins that are sleeping
show that one side of the dolphin's brain "awake" while the other in a deep
sleep ("slow-wave sleep"). Also, during this time, one eye is open (the eye
opposite the sleeping half of the brain) while the other is closed.

This type of sleep was thought to have evolved due to the dolphin's need to
breathe at the surface, but may also be necessary for protection against
predators, the need for toothed whales to stay within their tightly-knit
pods, and for regulation of their internal body temperature.

-Dolphin Mothers and Calves Get Little Sleep-

Unihemispheric sleep is advantageous to mother dolphins and their calves as
well. Dolphin calves are especially vulnerable to predators such as sharks,
and also need to be near their mothers to nurse, so it would be dangerous
for dolphin mothers and calves to fall into a full deep sleep as humans do.
A 2005 study on captive bottlenose dolphin and orca


Source: marinelife.about.com/od/Whales/f/How-Do-Dolphins-Sleep.htm

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