This is Bird Note. Some swifts and frigate birds stay aloft for months at a time.

Scientists know this because they attached sensors to the birds. What they hadn't been able to learn for certain

was whether birds might be sleeping on the wing and if they do for how long.

It was thought that one half of a bird's brain might sleep at a time, as happens with some

birds when resting on the ground. A 2016 study provided some solid answers. Tiny devices

attached to the heads of frigate birds, tracked electroencephalograph patterns,

and crucially, head movements. The results were fascinating. Frigot birds did sleep while

aloft. Most often, one half of the brain at a time, as suspected, but they also fell into normal, whole brain sleep and

sometimes even deeper REM sleep. But this deepest sleep came in bursts of just a few seconds,

during which time the bird's head dipped, but its flight pattern stayed steady, an in-flight

power nap.

So frigate birds do sleep on the wing, just not very much.

On average, 42 minutes per day.

When perched on land, they sleep 12 hours a day.

What still has scientists puzzled

is how they can get by with so little sleep

when flying for months at a time.

For Bird Note, I'm Mary McCann.