In this episode, we explore one of the most astonishing discoveries in animal science: some birds can actually sleep while flying.
For years, scientists wondered how birds manage nonstop flights that last for days—or even weeks—without collapsing to a window bird feeder from exhaustion. This study finally answered that question by recording brain activity from great frigatebirds as they flew over the ocean for up to 10 days straight. The results were surprising.
Using tiny brain sensors and GPS trackers, researchers discovered that frigatebirds do sleep in mid-air, but not the way humans do. Sometimes they sleep with one half of their brain at a time, keeping one eye open to stay aware of where they’re going. Other times, they briefly sleep with both halves of the brain, even while gliding thousands of feet above the ocean. These sleep episodes usually happen while the birds are circling on rising air currents, which helps them stay aloft safely (see Figures 2 and 3 in the article).
Even more surprising is how little sleep they get. While flying, frigatebirds sleep for less than one hour per day—only about 7% of the time they sleep when they’re on land. Their sleep in flight is also lighter and broken into very short naps, often lasting just seconds. The graphs on page 6 of the paper clearly show how dramatically sleep time and depth drop during flight compared to land-based rest.
This discovery challenges long-held beliefs about sleep. It shows that some animals can stay sharp, alert, and functional on extremely small amounts of sleep when survival demands it. The findings may even help scientists better understand sleep deprivation in humans—and how the brain copes when rest is limited.
