I spy with my duck's eye

Ducks sleep with half their brains awake

source: Alison Motluck
New Scientist February 6 1999 p8

Ducks can sleep with half their brains awake, according to research on mallard ducks, carried out by Indiana State University researchers. Niels Rattenborg and his team argue that birds maintain alertness in half their brains as a precautionary measure. They found that birds were more likely to sleep with one eye open if they were located on the edge of sleeping groups. These birds could detect video images of predators in less than a second. The birds were videotaped, and also given electroencephalograph tests, which showed that one brain hemisphere was in slow-wave sleep, and the other hemisphere, opposite the eye that was open, was alert. This research was reported in 'Nature', vol 397, p397.