Frigatebirds sleep for short bursts while flying -- one of the ways they can stay aloft for months at a time.
[Niels Rattenborg of Germany's Max Planck Institute for Ornithology (and other colleagues)] found it relatively easy to capture 15 of the birds to implant electroencephalographs (EEGs) into their skulls. Because EEGs measure electrical activity in the brain, the researchers were able to tell when the birds were awake or asleep. An implanted accelerometer clued them into how fast and in what direction the animals flew.
When they downloaded the data from the tiny devices a week later, the researchers found that while frigatebirds do sleep while flying, they sleep very little—about 45 minutes each day in short ten-second bursts, usually after dark. By contrast, on land, the birds sleep one minute at a time throughout the day and night for a total of roughly 12 hours each day.