Apart from their ability to fly, birds have another enviable ability - they can sleep with one eye open and half of their brain awake, researchers have said.It's called Unihemispheric Slowwave Sleep (USWs) and it allows birds to detect approaching predators while still getting a bit of shut-eye.Niles Rattenborg neuro-physiologist 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.