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Ducks Sleep Habits Studied

February 3, 1999

Researchers say ducks are capable of what teachers and bosses have suspected of the rest of us _ sleeping with one eye open.

After putting their ducks in a row, and videotaping them, researchers found mallards on the end of each row spent more time asleep with one eye open, apparently looking for predators.

The more the ducks felt threatened, the more they slept with one eye open, said lead author Niels C. Rattenborg, a graduate student at Indiana State University, Terre Haute.

``The unique aspect is not that they do it, but that they control it,″ Rattenborg said. ``When they sleep at the edge of a group they tend to perceive greater risk, so they spend more time sleeping with one half of their brain.″

Ducks with one eye open were still awake enough to detect predators, said the authors of the study, which appears Thursday in the journal Nature.

Researchers studied four groups of four ducks held in plastic boxes, which were arranged in a row. Ducks on the end were found to sleep with one eye open 31.8 percent of the time, compared to 12.4 percent of the time for ducks in the central position.

Also, ducks in the center did not open one eye more than the other, while ducks on each end kept the eye facing away from the group open 86.2 percent of the time.

Brain wave readings of the ducks showed that the half of the brain receiving signals from the closed eye indicated that half of the brain was sleeping. Signals from the half of the brain receiving signals from the open eye showed a state between fully awake and asleep.

Rattenborg said other animals, such as dolphins and other aquatic mammals show the ability to sleep with half their brains.

Other experts argue that those animals aren’t really sleeping at times when their eye is open.

Dr. David F. Dinges, director of sleep and chronobiology studies at the University of Pennsylvania School of Medicine, said the findings are important, but should be duplicated.

``If you said to many people, how would you like to sleep one hemisphere at a time while the other half of the brain works, most would jump at it,″ Dinges said. ``But, we don’t know the quality of the duck’s consciousness. We don’t know what the restorative potential of that sleep is.″

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