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Birds sleep with one eye open, half awake, study finds


February 3, 1999
Web posted at: 9:38 p.m. EST (0238 GMT)

LONDON (Reuters) -- Apart from flying, birds have another enviable ability -- they can sleep with one eye open and half of their brain awake, researchers said Wednesday.

It's called unihemispheric slow-wave sleep (USWS), and it allows birds to detect approaching predators while still getting a bit of shut-eye.

"They are able to make behavioral decisions about whether they keep one half of the brain awake or allow both halves of it to sleep," Niles Rattenborg said in a telephone interview.

The behavioral neurophysiologist at Indiana State University in Terre Haute and his colleagues believe their research, published in the science journal Nature, is the first evidence that an animal can control sleep and wakefulness simultaneously in different parts of the brain.

Dolphins, seals and manatees also have USWS, which lets them sleep and swim to the surface to breathe, but Rattenborg said birds seem to be able to use it at will.

"What was unique is that they are able to control it. They can also sleep with both halves of the brain. When they are sleeping under more risky situations, they increase the proportion of their sleep with one eye open and half their brain awake," he added.

Rattenborg thinks the research could have some implications for humans. Some sleep disorders, such as sleepwalking, are thought to occur when parts of the brain wake up while other parts are still sleeping.

"If birds can do it, humans might be able to do it in some form or another," he said.

There are even anecdotal accounts of war veterans who claimed that under extreme stress they were able to sleep with one eye open. But researchers have been unable to demonstrate it scientifically because it would involve putting a person under extreme stress. "We can't do that," said Rattenborg.

Copyright 1999 Reuters Limited. All rights reserved.

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