Birds have the ability for "Unihemispheric sleep"

Birds have developed an ability that let half their brain sleep while keeping the other half awake. Researchers report that ducks manage this trick to stay alert for predators while still getting some shut-eye. The findings suggest that different parts of the vertebrate brain can sleep independently of each other. 

 

Although researchers have known about this so-called "unihemispheric" sleep for 3 decades, they could only guess why this particular kind of shut-eye evolved in birds. But when filming mallards for a different experiment, sleep researcher Niels Rattenborg of Indiana State University noticed a remarkable pattern. 

 

The sleep pattern is as important as the amount, says Jerome Siegel, a sleep researcher at the University of California, Los Angeles. Each animal has evolved its way to balance the need for sleep with the need for safety.