Which birds can sleep while flying

Dispute decided Birds sleep in flight

Do birds sleep in flight or not? Scientists have been arguing about this for about 100 years. Some say: Of course, if birds can fly for days without a break, then they have to sleep. On the other hand, it was thought possible that birds could trick sleep. Example of gray-brood sandpipers in Alaska. They hardly sleep at all during their entire breeding season. Now the general question has been answered: birds actually sleep in flight. Usually, however, only with one half of the brain. The other, awake half is used for navigation, for example to use rising air currents, and not to collide with other birds.

Days of flights

The scientists at the MPI for Ornithology first built a small data logger together with experts from ETH Zurich - a device that can measure the birds' brain waves. Then they traveled to the Galapagos Islands, because the frigate birds that live there are known to fly over the sea for days in search of food. They stuck the device on their heads. Of course, this only works with a special adhesive, says Dr. Sabine Dehn from MPI Seewiesen: "We used Histoacryl, which is otherwise used to close surgical sutures." After the birds were back on land and had recovered for some time, they were caught again and the loggers removed. Bryson Voirin, research associate and second lead author of the study, was there himself: "Like many animals on the Galapagos Islands, the frigate birds were remarkably trusting and even slept when I caught them the second time."

The frigate birds keep one eye open to avoid colliding with other birds.

Dr. Niels Rattenborg

The data loggers measured brain waves in both hemispheres and head movements. A GPS device on the birds' backs provided the data on position, route and altitude. When the data were evaluated, it was clear: the animals sleep in flight. This sleeping behavior is also known from standing ducks. Those who sleep in the middle group sleep completely. Those who are on the outside, only with one hemisphere of the brain. "The frigate birds keep one eye open to prevent a collision with other birds, just like the ducks that keep an eye on potential predators," explains the head of the research team, Dr. Niels Rattenborg.

It's the same with dolphins, by the way. You also sleep with only one half of your brain to be able to continue swimming. However, the scientists also found complete sleep phases in gliding flight, albeit only very briefly, for a maximum of six minutes. Then only the head of the frigate bird sagged a little - but nothing more. So the muscle tone was retained. Not like humans, where the arms and legs slacken in sleep and dangle completely lifeless.

42 minutes of sleep at night

During the day, the birds stayed awake on their 3,000 km flight to look for food sources. During the night there were different phases of sleep - which made up a total of only 42 minutes per day. On land, the frigate birds sleep over twelve hours a day. The question is: how do birds manage to get by with so little sleep on their flight? Humans can't. Unfortunately, even in the car, we sometimes close our eyes after a few hours of driving. Now the researchers from the Max Planck Institute for Ornithology want to clarify the following questions: How can birds compensate for this lack of sleep, what effect does it have on their organism? And they hope to find new knowledge about sleep and the consequences of lack of sleep.