Why It’s Hard to Sneak Up on Sleeping Ducks

Q: Is it true that some animals sleep with only half their brain?

A: Yes. Electroencephalograms (EEGs) have shown that some species of birds and some aquatic mammals sleep with only half their brain at one time, while the other half remains alert and functioning. Such sleep habits allow the mammals to continue swimming and rise to the surface for air while at least part of their brain is getting a good night’s rest. The half of the brain sleeping apparently alternates. For birds, the ploy is apparently a way to keep on the lookout for predators. Researchers at Indiana State University recently reported that in a lineup of sleeping mallard ducks, the birds on the ends of the line kept their outer eye open and responded quickly to the presence of potential danger.