Birds observed sleeping during flight for first time, say scientists

Birds have been observed to sleep while in flight for the first time ever, according to new research.

Due to long-haul flights that can often last several days, weeks, or even longer, some sea birds have long been suspected of being able to fall fully asleep while “on the wing”, though it was not proven.

Now, researchers say they have evidence which shows birds can sustain sleep in flight.

Scientists from Max Planck Institute for Ornithology in Germany used a sample of 15 adult female frigatebirds - a species which spends long spells flying at sea - to test the sleep patterns.

Each bird had a small electroencephalogram (EEG) sensor fitted to record changes in the animals’ brain activity as they flew for up to 10 days and over 3,000km.

The readings showed that during flight, the birds could sleep using one hemisphere of the brain, or both together.

It was previously known that birds could sleep with one “half” of the brain, which allows them to keep one eye open and “connected” to the awake half to stay alert.

According to the paper, it is a sleeping technique used by frigatebirds for navigation.

"Frigatebirds sleep mostly while circling in rising air currents and keep the eye connected to the awake hemisphere facing the direction of flight, suggesting that they use unihemispheric sleep to watch where they are going," says the study, which was published in the journal Nature Communications on Wednesday.

The EEG readings also showed activity reflecting “slow wave sleep”, coupled with what the researchers believed to be a sleeping head position.

At points, the readings indicated apparent bouts of rapid eye movement (REM) sleep, the deeper phase of the sleep cycle, according to the study.

Despite the ability to fall “fully” asleep, the birds were found to do it less in the air compared to on land.

They slept “very little, in shorter bouts and less deeply” while in flight. This suggests that though it is possible, falling totally asleep is not ideal during flight due to the demand on the bird’s attention.

The researchers said the short bursts of sleep could be serving as “power naps” to keep the birds going until they return to land.

Further study could contribute to our understanding why sleep deprivation affects humans so badly and in such a “rapid” manner, according to the report.

“Determining how flying frigatebirds sustain performance on little sleep may provide new perspectives on our understanding of the adverse effects of sleep loss experienced in humans.”