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Re: Bird (Dinosaur?) vision
On Thu, 22 Jul 2004, Dino Guy Ralph wrote:
> From: "Jeff Hecht" <email@example.com> writes:
> > It has also been suggested that the birds may "doze" with eyes open
> > to watch for predators, while effectively getting some sleep.
> I had read that a group of sleeping birds perched single file along a branch
> or power line had lookout birds at each end of the formation. The birds on
> either end kept open those eyes which faced outward, away from the center of
> the group. These open eyes were conscious, and the brain apparently
> responded to the usual visual stimuli, but the brain was asleep aside from
> those functions that related to viewing and interpreting through the open
> eyes. In this way, birds truly do "sleep with one eye open."
February 3, 1999
Apart from flying, birds have another enviable ability -- they can sleep
with one eye open and half of their brain awake, researchers said
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.
> Regarding the alleged inability of birds to see nonmoving items, this seems
> absurd to me, especially in light of the fact that of all creatures birds
> possess perhaps the best visual acuity on the planet, but I would be happy
> to peruse evidence that supports such a claim.