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The Learning Kingdom's Cool Fact of the Day for February 24, 1999
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Why do some birds sleep with one eye open?
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Many kinds of birds sleep with only one half of their brain at a time,
keeping one eye open and one eye closed. They alternate which half of
their brain is awake and which half is asleep.
A recent study suggests that the reason is simple: the birds are
literally keeping an eye out for predators. Birds that are on the
edge of the flock are much more likely to sleep this way, and the eye
that is open usually faces out into the area surrounding the flock.
That way predators cannot approach without being seen.
Birds are not the only animals that sleep this way. Dolphins and
other sea-mammals sleep with only half their brains, but for a
different reason: they need to remember to swim to the surface to get
a breath of air.
People might also sometimes sleep with only part of the brain:
http://www.exn.ca/html/templates/htmlpage.cfm?ID=19990203-51
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Copyright (c) 1999, The Learning Kingdom, Inc.
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