If you look up to the skies above Londolozi at the moment you might see a tiny bird called the Alpine swift flitting about against the blue. Imagine being this tiny bird, weighing just 77g and yet being able to fly all the way from North Africa or Europe to Londolozi on your own steam. Then when you get here, for the next 200 days, you don’t touch land once. What has bemused researchers and ornithologists for many years is how it is these birds sleep without falling out of the sky. At last, we finally have some answers!

A male Alpine swift photographed during flight. These birds feed on small insects and can spend up to seven months in the air without landing, even drinking on the wing.

In a paper published in Nature Communications, Niels Rattenborg from the Max Planck Institute and colleagues from several other institutions have offered the first proof showing that flying birds can sleep with either one half of their brains active, or with both hemispheres shut down at the same time. Remarkably, these birds can retain their navigational ability while in REM sleep. In other words, they can literally fly with their eyes closed.

This technique of sleeping is called unihemispheric slow-wave sleep (USWS), which allows one half of the brain to enter into deep sleep while the eye corresponding to this half is closed and the other eye remains open. Unihemispheric sleep allows an animal to get some rest, while also allowing it to maintain awareness of its surroundings. In fact, dolphins also use this technique to avoid drowning while they rest.

Rattenborg and his team did their experiment on frigatebirds, who often spend weeks flying nonstop in search of prey.  What the study found was that these birds were flying upwards of 1,850 miles (3,000 kilometers) without stopping for a break. The birds would remain awake during the day while they looked for food and as the sun set they would enter into USWS for several minutes at a time.

A male frigatebird, easily recognisable by his red gular pouch, which he will inflate during the breeding season to attract females with. These birds feed predominantly on fish and squid chased to the surface by bigger fish such as tuna.

Occasionally, the birds even entered into REM sleep. You may think this is a crazy thing to do while flying but unlike us, where bursts of REM sleep are lengthy and involve complete loss of muscle tone, REM sleep in birds lasts for only a few seconds. That said, the resulting loss of muscle tone caused the heads of the birds to dip during flight, but amazingly it doesn’t affect their flight patterns.

A juvenile female great frigatebird, easily distinguishable from the male by its white underbelly. This bird is also known to scavenge from and kleptoparasitise other seabirds, snatching their food or stealing chicks from nests.

Despite their remarkable ability to sleep while flying, frigatebirds still get excruciatingly little sleep. On average, they sleep for only 42 minutes a day. This is similar to the giraffes we see here who only sleep for about 30 minutes every day. Unlike the giraffe who only needs minimal sleep, the frigatebirds are used to sleeping for about 12 hours a day when on land. This suggests that frigatebirds are seriously sleep deprived during their foraging flights. How they’re able to function with such little sleep remains a mystery.

A male frigatebird, settled down and incubating an egg. Despite being able to soar for weeks on wind currents, these birds form nesting colonies during the breeding season. The duration of parental care is among the longest of any bird species meaning frigatebirds are only able to breed every other year.

Despite gaining knowledge of how Alpine swifts fly while sleeping, we still have no idea why they choose not to land during their foray down south. Not all of them do this, and some certainly do land to breed. Certain individuals however, have been shown though electronic tags in a study by the Swiss Ornithological Institute, to spend more than 6 months aloft!
Although I may be biased, South Africa’s Lowveld seems like a pretty fabulous place to spend a summer and to kick it back for a nap every now and again. The beauty of the unknown though is that it reminds us how relatively little we understand about the creatures we share the planet with, which means we can only continue to learn about the mystery we all form a part of.

Filed under Birds Wildlife

About the Author

Amy Attenborough

Media Team

Amy has a rich field-guiding history, having spent time at both Phinda and Ngala Game Reserves. This diversity of past guiding locations brought her an intimate understanding of different biomes across South Africa, and she immediately began making a name for herself as ...

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10 Comments

on How Do Birds Manage To Sleep On The Wing And Not Crash?

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Marinda Drake

Interesting blog Amy. We see the Alpine swifts often, always darting around. Did not realize that they never make landfall. Do they not come to Africa to breed? Do they make the mud nests underneath the bridges?

James Tyrrell

Hi Marinda. Apologies, the study showing that some Alpine swifts can go 6 months without touching down wan’t meant to apply to ALL individuals. Some certainly do land and breed.

Joanne Wadsworth

Now I have heard it all! Seemingly impossible, yet plausible when explained. What an incredible world we live in and in certain ways have only scratched the surface of knowledge and understanding. I’m going to have to re-read this again. Thanks Amy.

A B

Yesterday saw a flock of Alpine Swift Birds (I think!) flying around our locality…was quite mesmerized watching them gliding and soaring about, the aerobics continued for 2-3 hours ….finally got an explanation and name of the bird that quite caught my heart 😀

Callum Evans

Very interesting article! I hope that researchers figure out the how and the why soon. It’s always baffled me why swifts never land.

Lucie Easley

It is really amazing what we continue to learn about other species that belong to this planet. May this knowledge be welcomed with a renewed energy to save the planet and all who dwell here. Thanks, Amy, for another learning experience for me. Happy Holidays

Jeff Rodgers

Incredible story and not surprising that bird scientists don’t really know all of the ‘why’ of this.

Denise Vouri

Fascinating!! I love learning more about the animals in our planet. Seems incredible that giraffes sleep only 30 minutes a day. I’d be a disaster!! Keep writing your informative blogs.

Michael & Terri Klauber

Amy, Wow, thanks for the educational info – pretty amazing! We bet all of you will need LOTS of sleep after the holiday! Merry Christmas to all!

James Tyrrell

Thanks Michael and Terri! And a Merry Christmas to you both and everyone in Sarasota!

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