This odd habit by our feathered friends has long been theorised, but now German scientists say they have definitive proof for the first time ever.
Scientists at the Max Planck Institute in Seewiesen, Bavaria, announced they had proved that birds can fly while sleeping and still stay aloft.
The researchers monitored the brainwaves and movements of great frigate birds from the Galapagos Islands, whose airborne journeys may last for months.
They strapped devices to the heads of female birds to measure brain activity over the course of 10 days.
They found that these winged wildlife require less sleep while making their long flights over the ocean than they do on land, the scientists wrote for the journal Nature Communications.
“It is commonly assumed that flying birds maintain environmental awareness and aerodynamic control by sleeping with only one eye closed and one cerebral hemisphere at a time.
“However, sleep has never been demonstrated in flying birds,” the researchers wrote.
The study found the birds slept roughly 42 minutes per day, a fraction of the more than 12 hours of sleep they normally get on land.
“In addition to establishing that birds can sleep in flight, our results challenge the view that they sustain prolonged flights by obtaining normal amounts of sleep on the wing.”
Sometimes the birds were in a way half a sleep: one hemisphere of their brains would be awake to detect potential threats with the respective eye open.
“The frigate birds may be keeping an eye out for other birds to prevent collisions much like ducks keep an eye out for predators,” said lead researcher, NielsRattenborg.
But the birds were also at times able to keep both brain hemispheres asleep without crashing.
What remains unclear is why the birds maintain such low amounts of sleep, even at night when they don’t need to be alert to hunt.
“Why we, and many other animals, suffer dramatically from sleep loss whereas some birds are able to perform adaptively on far less sleep remains a mystery,” Rattenborg said.
