What birds are able to sleep while flying?

The great frigatebird has actually been observed to sleep while flying! An alpine swift has been observed to stay in the air flying for 200 days straight! So while the bird was not specifically seen sleeping, it is likely that the bird did. The albatross also can stay in the air for months at a time leading to another species that likely sleeps while flying.

The frigatebird was of particular interest as it would spend up to 2 months out in the open sea...but it can't swim. So if it did land for a moment to catch a break it would drown. Amazingly they were able to implant a chip and find that the birds DO actually sleep for short 10-second clips!

Rattenborg was also drawn to frigatebirds for logistical reasons. One nesting population of the species in the Galapagos Islands is “quite tame” after years of constant observation, he says. Rattenborg and his team 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.

https://www.audubon.org/news/scientists-finally-have-evidence-frigatebirds-sleep-while-flying