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Birds that are literally half-asleep-with one brain hemisphere alert and the other sleeping-control which side of the brain remains awake, according to a new study of sleeping ducks. Earlier studies have documented half-brain sleep in a wide range of birds. The brain hemispheres take turns sinking into the sleep stage characterized by slow brain waves. The eye controlled by the sleeping hemisphere keeps shut, while the wakeful hemispheres eye stays open and alert. Birds also can sleep with both hemispheres resting at once. Earlier studies have documented half-brain sleep in a wide range of birds. The brain hemispheres take turns sinking into the sleep stage characterized by slow brain waves. The eye controlled by the sleeping hemisphere keeps shut, while the wakeful hemispheres eye stays open and alert. Birds also can sleep with both hemispheres resting at once. Decades of studies of bird flocks led researchers to predict extra alertness in the more vulnerable, end-of-the-row sleepers, Sure enough, the end birds tended to watch carefully on the side away from their companions. Ducks in the inner spots showed no preference for gaze direction. Also, birds dozing(打盹)at the end of the line resorted to single-hemisphere sleep, rather than total relaxation, more often than inner ducks did. Rotaing 16 birds through the positions in a four-duck row, the researchers found outer birds half-asleep during some 32 percent of dozing time versus about 12 percent for birds in internal spots. | 
