A bird keeps half of its brain awake while it sleeps
Birds, dolphins and other aquatic mammals perform unihemispheric slow-wave sleep (USWS) which puts one half of their brains to sleep while the other half stays alert. Animals that do this actually keep one eye open while the other sleeping eye stays shut. They don't always split their brains' sleep time, but when they need to stay in motion or are on high alert for predators, they can downshift and go to sleep, one half of their brain at a time.
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