How frigatebirds stay aloft for weeks and weeks

Great frigatebirds (Fregata minor) are marvels of nature, for they’re known to stay aloft—without landing—for weeks and even months, though they have to descend to the water’s surface to fish. And it’s a good thing, too, for, unlike nearly every other seabird, their feathers aren’t waterproof and their legs are too small to land on the water. That could be tricky, as they make their living by catching fish from the ocean. (Of course, these features could have evolved after their aerial habits or have coevolved with them.) Frigatebirds have the largest wing area/body mass ratio of any living bird, and their only rivals in staying aloft are swifts, which can also remain in the air for months without resting or sleeping.

Here’s a great frigatebird on the wing, and those wings are huge:


West of Christmas Island, Kiribati, November 21, 2012 © Donald H. Gudehus. Source.

The males have red gular sacs that they inflate to attract females during the breeding season (photo from Wikipedia).


Here’s their range:


How do these birds manage to stay aloft for so long? Do they sleep on the wing? A team of researchers headed by Henri Weimerskirch give some answers in a paper published in the July 1 issue of Science (free download, reference and link below).

The answer is that the birds have a very low expenditure of energy, flapping their wings as rarely as possible. They accomplish that by taking advantage of wind and weather. To track these birds and their energy expenditure, the team put solar-powered transmitters on 49 birds (24 adults, 25 juveniles) caught on the island of Europa between Madagascar and mainland Africa. An additional 11 adult females were fitted with “loggers” measuring their GPS location, acceleration, and heart rate. The birds were tracked when they left Europa after the breeding season ended and moved northward to fish.

During this period, birds were continuously aloft except for occasional resting periods—landing on islets for only 8-48 hours. On average, the birds’ maximum time aloft was 41.2 days each, with the record being 2.1 months in the air without a rest. The researchers knew this because they could monitor the altitude and position of the birds. On average, a bird traveled between 420 and 450 km per day (260-280 miles, greater than the distance between New York City and Washington D.C.), depending on whether they were circling around the doldrums (see below) or traveling in a directional way.

So how do they stay in the air so long without exhausting themselves? The researchers found several things:

  • During the period these birds were aloft, there are areas of no wind (“doldrums”) between Madagascar and India. The transmitters showed that the birds flew around the edges of these doldrums, for those edges have updrafts the birds can use to gain altitude without expending energy. Here’s a track of a single adult male. The colors, as indicated on the scale, give wind speeds in meters per second (it’s zero in the doldrums). All figure captions are from the paper:
Screen Shot 2016-07-06 at 9.16.04 AM

Two successive clockwise movements from Aldabra Island (Seychelles) of an adult male great frigate bird (no. 138502) in relation to wind strength (in meters per second, color scale) and direction (arrows). (A) In May 2015, a 24-day foraging trip around the doldrums (shown by the absence of wind, in white), with 1 day of rest in Chagos. (B) In June 2015, a 28-day foraging trip, with a 36-hour rest in Chagos.

  • The birds gain altitude for soaring (which then allows them to glide downward without expending energy) by moving with the wind, using thermal updrafts to lift them. They then glide down with the wind at their side. Here’s a diagram of that movement, which the authors describe as “a complex zig-zagging roller-coaster movement”. They go up about 600-700 meters in each rise before a gliding descent:

Fig. 3 Three-dimensional movement of a frigate bird at three scales. (A) Section of a track of a frigate bird traveling with side winds. (B) Enlargement showing the movement alternating gliding and soaring, resulting in a zig-zag and roller-coaster movement. (C) Detailed schematic representation of a single cycle of soaring and gliding, illustrating the climb by circling, with a resulting drift due to wind, followed by the descent.


  • Perhaps the most surprising finding is this: the birds deliberately fly up into cumulus clouds, which have strong updrafts. Inside those clouds the birds can ascend at 5 meters/second, and they can go as high as 4000 meters, where it’s below freezing! Then they glide down, and after such a big rise can then glide about 60 kilometers without flapping. Juvenile birds do this, too, suggesting that this behavior isn’t learned but genetically hard-wired.
  • Finally, do they sleep? The authors don’t know, and neither does anyone else. Here’s what they say:

“Long periods in continuous flight are interrupted by very short periods of rest on land, suggesting that frigate birds might sleep while airborne. Periods of low activity (no flapping) occur mainly during soaring episodes and may allow sleep. However, periods of completely motionless (no flapping at all) flight, potentially corresponding to periods of sleep, are relatively short, (~2 min, never exceeding 12 min). Animals such as frigate birds may have evolved the ability to dispense with sleep when ecological demands favor wakefulness such as during extended flights, but studies are needed to determine how they sleep during much longer-lasting flights.”

I’m sure there are many readers who would appreciate an evolved ability to dispense with sleep! It is a big mystery why these birds can do it (if they do it), while other animals absolutely require sleep if they’re to live. At any rate, we have yet another study that, using modern technology, is able to uncover how much more wonderful animals are than we ever suspected.

Here’s a video of these birds, produced to illustrate the findings of Werimerskirch et al. Sadly, it uses a robotic voice.


Weimerskirch, H., C. Bishop, T. Jeanniard-du-Dot, A. Prudor, and G. Sachs. 2016. Frigate birds track atmospheric conditions over months-long transoceanic flights. Science 353:74-78.


  1. loren russell
    Posted July 6, 2016 at 10:21 am | Permalink

    I first read this report as “these birds are pelagic for eight months.” Then realized that they are literally airborne for up to eight months! And live over open ocean but can’t take off from water! And — I think this is the weirdest — they are able to survive by catching flying fish [and I suppose, flying squid]. This is just mind boggling to a temperate zone landlubber like me…. flying fish are a reliable food source over evolutionary time, not just on the road to Mandalay!

    I wonder if the latter was true in the Mesozoic — were many of the pterosaurs able to do pretty much what the frigate birds do now? It might be flying belemnites, of course..

    • gravelinspector-Aidan
      Posted July 6, 2016 at 4:38 pm | Permalink

      I wonder if the latter was true in the Mesozoic — were many of the pterosaurs able to do pretty much what the frigate birds do now? It might be flying belemnites, of course..

      Belemnites are not really “flight shaped.” OTOH,

      Oldest flying fish fossil found in China
      Fish could glide over water as early as middle Triassic.

      (paper here, including FREELY downloadable PDF) Flying fish (well, “gliding over water” neopterygians) have been dodging fast-moving water-bound predators for a while.

      • gravelinspector-Aidan
        Posted July 6, 2016 at 4:45 pm | Permalink

        Mid-triassic (Ladinian) is 237 to 242 million years ago (ISC 2015 timescale)

    • Jeff Lewis
      Posted July 7, 2016 at 9:02 am | Permalink

      When I read ‘dinosaur’* books as a kid, it seemed like everyone thought pterosaurs were underpowered fliers that could only take off by jumping off of already high points like cliffs, and that the vast majority of pterosaurs ate fish that they hunted out over the ocean. Of course, seeing what kids books are like now, I’m not sure how accurately that reflected the prevailing scientific view of the time, but it still seems to be the most prevalent popular view among lay people. Anyway, a lot of what I’ve been reading in the last few years challenges that traditional view – from athletic quadrupedal takeoffs, to terrestrial stalking as a hunting strategy. In fact, it seems as if most pterosaurs probably didn’t eat fish, or at least didn’t specialize for them. Here are a couple articles on Mark Witton’s blog related to this:

      *Because obviously, pterosaurs aren’t dinosaurs. Neither is Dimetrodon, which was almost always included in those types of books, as well.

      • Jeff Lewis
        Posted July 7, 2016 at 9:13 am | Permalink

        Hmm, I posted all that without actually getting to my point. While some pterosaurs may have had hunting strategies similar to frigate birds, I doubt it was many of them.

  2. Frank Bath
    Posted July 6, 2016 at 10:44 am | Permalink

    A valuable piece of research. An awesome wonder of nature, almost living in the air. It isn’t explained but presumably they feed by taking fish from the sea’s surface. How is this done and how often?

    • loren russell
      Posted July 6, 2016 at 12:59 pm | Permalink

      This is what I was riffing on, from an NPR story:

      “Frigatebirds have to find ways to stay aloft because they can’t land on the water. Since their feathers aren’t waterproof, the birds would drown in short order. They feed by harassing other birds in flight until they regurgitate whatever fish they’ve eaten and the frigatebird takes it. Or they fly over a fish-feeding frenzy on the ocean surface and scoop up small fish that leap out of the water to escape larger fish.”

      So not necessarily flying fish [tho these would be very welcome], but aerial. Aside from take-aways from other piscivorous birds.

      Note that frigate bird beaks are long, very elegant forceps, but not at all built for skimming or dip-netting in flight. As was the case for so many of the piscivorous pterosaurs, IMO.

  3. µ
    Posted July 6, 2016 at 10:45 am | Permalink

    How cool!
    Next cycle-of-life I hope to be reborn as a frigatebird.

    Re possible absence of sleep: frigatebirds may have uni-hemispheric sleep, such that left and right brain hemispheres alternate sleep at different times. Cetaceans and many birds are known to do this.
    REM-sleep (with complete muscle relaxation) may have evolved to be different, though.

    • nickswearsky
      Posted July 6, 2016 at 11:30 am | Permalink

      This is what I thought too. I believe many ducks are capable of this type of sleep.

    • Posted July 6, 2016 at 2:39 pm | Permalink

      Also, I have read that birds can microsleep–short periods of sleep interspersed with wakefulness.

      • µ
        Posted July 6, 2016 at 4:09 pm | Permalink

        I always micro-sleep during endless faculty-meetings. Sometimes macro-sleep

        • gravelinspector-Aidan
          Posted July 6, 2016 at 4:49 pm | Permalink

          Someone is marked for greatness. [G]

  4. Gregory Kusnick
    Posted July 6, 2016 at 11:37 am | Permalink

    Surely that “wind” arrow in Fig. 3 should be standing on its tail, if the birds are climbing on updrafts.

  5. Michael Fisher
    Posted July 6, 2016 at 11:39 am | Permalink

    Perhaps a hemisphere of brain sleeps – I found the term “unihemispheric slow-wave sleep” via google & there’s a [url=]WIKI ON THE SUBJECT[/url]

    • Michael Fisher
      Posted July 6, 2016 at 11:40 am | Permalink

      Ooops Maybe this works better

      • Michael Fisher
        Posted July 6, 2016 at 11:42 am | Permalink

        I’ve repeated somebody elses comment above me, sorry. It wasn’t there when I posted, but no it shows as being posted an hour ago [Perhaps moderated I spose]

  6. Jonathan Wallace
    Posted July 6, 2016 at 11:43 am | Permalink

    Fascinating. Frigatebirds are not the only birds to spend extraordinary periods of time in flight. I believe swifts Apus apus (and other members of the Apodidae) perhaps spend even more time continuously in flight – as far as I know, apart from nesting they spend their entire lives on the wing). These birds are much smaller than Frigatebirds with a very different aerodynamic ‘design’ and so must depend on different strategies for keeping airborne.
    Swifts also have very short legs and if they do – by mishap – end up on the ground they are unable to get back into the air. They nest high up on buildings or natural cliffs which enables them to get airborne when they leave the nest.

    • Jonathan Wallace
      Posted July 6, 2016 at 11:46 am | Permalink

      Apologies – just noticed that swifts were already referred to in the original post.

    • Jeff Lewis
      Posted July 6, 2016 at 12:06 pm | Permalink

      Here’s a link to an article on a study done on swifts:

      Similar to this albatross study, lightweight sensors were mounted on the birds to monitor their behavior, confirming with hard data what had been speculated before – that the birds remain aloft continuously for over 200 days straight, and only land during the breeding season. And although that article doesn’t mention it, other sources I’ve read claim that they even mate in the air, and only land to build the nests and rear their young. Considering that they don’t reach sexual maturity until they’re 2 years old, I wonder what the younger ones do. Since they’re not breeding, do they just continue to fly for over a year straight?

      • Jeff Lewis
        Posted July 6, 2016 at 12:13 pm | Permalink

        Sorry – that should read ‘Similar to this frigate bird summary…’. But after spending my lunch break reading about different types of birds that spend a lot of time on the wing, I guess albatross got stuck in my head.

      • Gregory Kusnick
        Posted July 6, 2016 at 12:15 pm | Permalink

        I’m guessing that the adaptations needed to stay aloft for, say, 30 days are sufficient to stay aloft indefinitely. So 200 days or a year or more are effectively equivalent; at that point it’s really a question of whether there’s any reason to come down.

        • Posted July 6, 2016 at 1:30 pm | Permalink

          There could be nesting and incubation constraints. That’s a good reason to come down.

        • Jeff Lewis
          Posted July 7, 2016 at 9:17 am | Permalink

          Gregory Kusnick – exactly what I was wondering. Do the sexually immature individuals have any reason to come down, or do they just stay constantly in flight until they’re 2 years old.

  7. Kevin
    Posted July 6, 2016 at 12:01 pm | Permalink

    Unreal. World class travelers.

  8. Posted July 6, 2016 at 12:01 pm | Permalink

    I thought I heard somewhere that some mammals (so maybe it evolved in birds convergely?) are able to microsleep (seconds or something at a time.)

  9. Posted July 6, 2016 at 12:27 pm | Permalink

    They should have put some cameras on the birds too! I hope someone does it and we learn more about these fascinating birds.

  10. Hempenstein
    Posted July 6, 2016 at 12:42 pm | Permalink

    Fascinating and way cool.

    My own avian mystery, from an experiment I inadvertently ran once, is how are pigeons able to go for at least a week without water? By the time I finally caught them they didn’t seem any the worse for wear, either.

    • Gregory Kusnick
      Posted July 6, 2016 at 1:03 pm | Permalink

      Well, bird urine (as you know if you’ve ever had to clean it off your windshield) contains a lot less water than ours does.

      Which of course just flips the question around: why do mammals require a continuous flow of water through their system?

      • gravelinspector-Aidan
        Posted July 6, 2016 at 4:57 pm | Permalink

        Not all do – some barely pee. Desert-adapted species in particular.
        Which my be an indicator to the evolutionary environment of the Urvögel.
        Which reminds me – have I done my daily slice of German?

  11. Randall Schenck
    Posted July 6, 2016 at 12:49 pm | Permalink

    The ultimate glider, far beyond anything a human can do. The ability to perfect this type of aerodynamics, living and eating on the fly is hard to understand.

    When I am out mowing, as I do often, the purple martins will suddenly show up and perform their mastery of the air shooting by on all sides, making sudden 180 degree turns and dives while catching the extra bugs thrown up by the mower. When you first see this you think they will fly into something but they never do.

  12. Mark Sturtevant
    Posted July 6, 2016 at 2:19 pm | Permalink

    This is very interesting, and I enjoyed learning about these awesome birds.

  13. J Cook
    Posted July 6, 2016 at 2:27 pm | Permalink

    some birds seem to sleep one half of their brain at a time. closing one eye for a few seconds and then the other. Swallows?

  14. Posted July 6, 2016 at 3:09 pm | Permalink

    As an Animal Planet movie said about these birds, “they are as close as possible to the ultimate bird, the one that never touches down”.

  15. Lars
    Posted July 6, 2016 at 3:36 pm | Permalink

    Interesting summary – thanks for doing this.

    Something that I’ve wondered about when reading of these bird species that spend huge amounts of time on the wing – why don’t their wings get tired? You’d think that prolonged extension of these limbs would result in exhaustion.

    • Gregory Kusnick
      Posted July 6, 2016 at 4:41 pm | Permalink

      My guess is that their wing joints work like umbrellas that latch open. It then takes muscular effort to disengage the latch and refold them.

    • gravelinspector-Aidan
      Posted July 6, 2016 at 5:19 pm | Permalink

      why don’t their wings get tired

      They do. That’s why they glide.
      The flight muscles of birds are gigantic in relation to their body mass. If you scaled up your pectorals to match a (poor) flier like a chicken, they’d be 15cm thick over your ribs and reach down to your abdomen. They’re probably also composed of multiple sections that are individually controllable, allowing one segment to be rested while others are doing the work.

  16. rickflick
    Posted July 6, 2016 at 4:21 pm | Permalink

    Animals ARE cooler than you might think. I saw frigatebirds nesting in the Galapagos years ago. The males were positively embarrassing with their red throats pumped up like over-inflated beach toys. Such new details about their flight is welcome indeed.

  17. Mark R.
    Posted July 6, 2016 at 4:27 pm | Permalink

    The only time I’ve seen photos of frigate birds were of the males’ red gular sacks. I had no idea of their uncanny abilities. Thanks for highlighting these amazing birds.

    And as for hitting altitudes of 4,000 meters, I’d imagine it’s the longest aloft and highest aloft bird.

    • gravelinspector-Aidan
      Posted July 6, 2016 at 5:26 pm | Permalink

      Not highest by a long chalk. Geese have been seen flying above Chomolungma (a.k.a. Mt Everest). That’s in the region of 9km, and is only the highest observation. If some bird chooses to use the jet stream to assist migration, there’s several km more it can go up.
      We don’t know what the highest that birds can fly at is ; we only know the highest they’ve been seen at.

      • loren russell
        Posted July 6, 2016 at 7:31 pm | Permalink

        Yes, flying above the death zone for us… and likely most or all mammals. Birds just got it right while we furries are stuck in the Permian.

        As a cyclist, I’d love to have some of those goose ventilation circuits.

        • gravelinspector-Aidan
          Posted July 10, 2016 at 8:30 pm | Permalink

          You’re probably encroaching on patents that some cycling team is planning on introducing.

      • Mark R.
        Posted July 6, 2016 at 8:08 pm | Permalink

        Cool. Thanks for breaking my perceived record. Geese flying over Mt. Everest?…hmmm…now that is a mind-fu*k.

      • Jonathan Wallace
        Posted July 7, 2016 at 6:56 am | Permalink

        Bar-headed geese, Anser indicus, I believe.

  18. keith cook + / -
    Posted July 6, 2016 at 5:21 pm | Permalink

    For a bird interested person it made me wonder if frigates have a strategy for flying in the rain given that those large wings are not water proof and since they are all about energy conservation, would not rainwater add weight and drag?
    The fact that they can reach high altitudes, so it’s possible for them to fly above storms or do they evade storms like doldrums… that said they would need to plan as it were i.e. look for updrafts or does the air moving over the wing keep water build up to a minimum so little difference to their flight capabilities and use of energy.

    • gravelinspector-Aidan
      Posted July 6, 2016 at 5:26 pm | Permalink

      Good questions.

    • rickflick
      Posted July 6, 2016 at 7:56 pm | Permalink

      Yes, good questions. Inside a cumulus cloud, where updrafts may serve them well, what of the downdrafts and torrential rain and even hail that sometimes accompanies these structures?

  19. eric
    Posted July 6, 2016 at 7:34 pm | Permalink

    Very cool. Thanks for the post!

  20. Scott G
    Posted July 6, 2016 at 8:37 pm | Permalink

    For anyone interested:

    I found two references to EEG and sleep in reptiles (Caimans) and songbirds. Able to obtain pdf downloads for free at the links below.

    Imaging the lab tech connecting the electrodes to the Caiman makes me smile.

  21. Richard Bond
    Posted July 7, 2016 at 5:35 am | Permalink

    Many years ago, New Scientist had and article explaining that some species of albatross manage to stay aloft over the sea without flapping by exploiting the difference in wind speed with height above the waves. They used a zig-zag path that, as I recall, looked very like diagram C.

    • Jonathan Wallace
      Posted July 7, 2016 at 7:07 am | Permalink

      A number of different bird groups have evolved very efficient methods for flying long distances with minimal effort. As well as the gliding technique you describe for albatrosses, many large migratory birds use a soaring and gliding technique based around the exploitation of thermals. These birds which include storks, vultures and various raptors, are broad winged and they circle in warm rising air (ie thermals) until they have attained great altitude and then travel in a shallow glide over longs distances (tens of kilometres).
      Because thermals do not develop over sea-water these birds avoid long sea crossings which results in their migratory routes being concentrated through short crossing points which in turn makes these locations honeypots for birdwatchers. With European birds there is a divide with eastern populations migrating around the eastern Mediterranean and into Africa and western populations migrating down through Spain and across into Africa at Gibraltar.

  22. Richard C
    Posted July 8, 2016 at 2:23 am | Permalink

    2 months without landing! These birds are absolutely amazing.

    Thanks for the post!

  23. jeffery
    Posted July 12, 2016 at 10:48 am | Permalink

    Stephen Baxter, in his novel, “Evolution”, postulates the existence, up until the Cretaceous impact, of “floaters”- giant gas bag organisms that survived in the upper atmosphere feeding on dust and pollen. Their bodies were so fragile that no evidence of them was preserved (he also postulates intelligent, bipedal dinosaurs in the Jurassic period).

    • Gregory Kusnick
      Posted July 12, 2016 at 11:46 am | Permalink

      Warning: SF nerd ahead

      The idea is not original with Baxter. Floating gasbag creatures have been a staple of SF since at least the 1970s. They were featured in the Medea collaboration organized by Harlan Ellison in 1975; James Tiptree Jr. had them in Up the Walls of the World in 1978; and John Varley used them in Titan in 1979, to name just a few.

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