Scientists for the first time failed to notice that birds can sleep while flying. So far it was only assumed that birds have this ability, but there was no evidence of that.
But while scientists thought it is possible, new research shows that the way the birds sleep in the air is much weirder than what was assumed.
This discovery will help to resolve the dilemma around how birds manage to fly for days or weeks without being lowered to the ground, which for decades divided the opinions of naturalists.
Without knowing exactly what is happening in the air, scientists were not sure whether the birds are awake during the entire flight, or they rest only one hemisphere of the brain, while the other is active. Just as ducks do on earth to protect themselves from predators.
The research was done on a skimmer (frigatebird), which is known to be able to fly for weeks over the ocean in search of fish. A team of scientists from the Department of Ornithology of the Max Planck Institute in Germany did the research.
They made a small device, electroencephalography (EEG), which measured the brain activity in the bird. Such a device was hung on 15 adult females. Scientists monitored the brain activity of the birds for 10 days and more than 3,300 km flight. While the position and height of the birds was monitored by a GPS device.
The data was collected after the birds landed on the ground for a rest. The data analysis showed that while flying through the day looking for fish, birds were awake. But after sunset, the birds enter into sleep mode a few minutes, all the while still flying over the water.
It is, mostly, what was expected, they rest only one hemisphere of the brain.
Besides ducks, this phenomenon is also found in dolphins that can swim while sleeping, with one hemisphere of the brain awake to “beware” of possible dangers. People also do this when they sleep in a new place.
The device data showed that in birds only one hemisphere is associated with the eye that follows the direction of movement while flying. This suggests that the bird keep one eye open so as not to clash with other birds. Just as ducks watch out for predators, the researchers said.
However, EEG recordings also showed that both hemispheres simultaneously enter the state of sleep. Indicating that they can maintain control of aerodynamics until the entire brain is “asleep.”
In rare cases, the birds go into REM phase of sleep and fail to hold in the air. Which is very unusual, because with most mammals REM occurs at a stage of complete relaxation of the musculature. But in birds, the REM stage lasts only a few seconds during the flight. And the only noticeable sign of muscle relaxation is lowering the head.
The results obtained while the birds are on the ground have shown that they can be at this stage and stand on one leg as well.
Apart from all these unique capabilities, the most surprising was the fact that these birds slept less than an hour a day. Or an average of 42 minutes, which is 10 percent less than the time you normally spend in bed.
Why do birds sleep so little when flying remains unclear. Even at night when you can not come up with a lot of food, the researchers said.