Scientists were finally able to prove that birds can fall asleep mid-flight after a recent discovery explained how birds can fly for days and weeks without ever needing to land. A team from the Max Planck Institute for Ornithology came up with a tiny device that measures the electroencephalographic (EEG) changes in the bird’s brain activities. Dubbed the flight data recorder, this was used to detect slow wave sleep and REM sleep, and was attached to 15 adult female frigatebirds.

Ten days and over 3,000 kilometers later, the team retrieved the flight data recorders and what they found was surprising. During the day, the birds would stay awake in search of food and at nighttime, they switched into slow wave sleep for a few minutes while flying over water. The data also revealed that frigatebirds kept their eyes opened connected to one hemisphere facing the direction of the turn when circling on rising air currents. This behavior prevents them from colliding into other birds.

The EEG recordings also suggested that they were able to maintain aerodynamic control even with their brain asleep, as scientists found that the frigatebirds go into REM sleep for a few seconds mid-flight. Surprisingly, despite this ability, frigatebirds only sleep 42 minutes a day on average — less than 10% of their normal sleep time on land. While more research needs to be conducted to understand how the birds function with minimal sleep, this latest discovery is a starting point.