The researchers from Max Planck Institute of Ornithology discovered sleeping birds flying in the sky.
The study monitored the brain activity of frigatebirds and found that the birds could deactivate one or two hemispheres simultaneously while they are flying.
The birds can engage in all types of sleep, but the total duration is of less than an hour each day while up in the air. However, on land, the birds sleep normally. The researchers are still wondering how the frigatebirds manage to function correctly with so little sleep.
Some species of birds, such as the sandpipers, songbirds, and seabirds can fly without stopping for months while traversing the planet. As sleep loss has a powerful effect on performance, the scientists assumed that birds would have got their resting time while being up in the sky.
Birds can either turn their both hemispheres off or just one of them. The biologists already knew the example of the mallards, who keep one brain hemisphere on when sleeping at the edge of a group. Dolphins can also sleep unihemispherically while they are swimming. Thus, the ornithologists presumed that birds could do the same while flying.
Another possibility is that birds managed to develop a cheating method.
The researchers used a device for measuring the electroencephalographic changes in the brain of the flying birds. The instrument was temporarily attached to the head of the female frigatebirds nesting on the Galapagos Islands.
The researchers recorded the brain activity for periods of flights of up to 10 days non-stop and 3,000 kilometers, while a GPS also recorded their route and their stops.
After the birds had returned to land, the researchers removed the equipment, and they were amazed by the fact that the Galapagos animals were calm and were even sleeping while they were removing the devices.
The results show that the frigatebirds would sleep for short periods of time during the night, with just one or both hemispheres. However, they slept more unihemispheric than they usually sleep on land.
Moreover, when sleeping unihermispherically, the frigatebirds would keep active the part of the brain facing the wind direction, which means they were still controlling their flight and were trying to avoid collisions. While mammals need more REM sleep, birds can go with only a couple of seconds of profound sleep per night.
The flying frigatebirds sleep only 42 minutes each night. On the contrary, when back on land they sleep for over 12 hours each day, with longer and deeper episodes of sleep.
Image Source: Wikipedia