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Some birds, such as the great frigatebird, can sleep while flying during long journeys over the ocean. Scientists discovered that these birds use unihemispheric slow-wave sleep, meaning one half of the brain sleeps while the other half stays awake. This allows them to continue flying, avoid collisions, and remain aware of their surroundings. During migration, they may sleep only a few minutes at a time while soaring on air currents.
Once they return to land, they make up for the lost sleep by resting for much longer periods. This remarkable adaptation helps them stay airborne for days or even weeks.
© Max Planck Institute of Animal Behavior