Can birds fly into a headwind that is faster than their own maximum speed?

I just read this snippet in Gerald L. Wood’s fascinating Guinness Book of Animal Facts and Feats, 3rd edition [amazon.com, amazon.co.uk]:

(I’ll just type that out, mostly for the benefit of search engines.)

Some birds can fly into a wind with a greater velocity than their own maximum speed and still move forward, although the reasons for this are not known.  Meinertzhagen once saw a small group of common eider (Somateria mollissima) perform this remarkable feat in South Uist, Outer Hebrides during a 90-95 mile/h 145-153 km/h gale.  ‘This particular wind was so strong’, he writes, ‘that shooting was out of the question, wild swans were grounded and unable to rise and we experienced the greatest difficulty walking against it.  Eider duck had come inland from the sea and were sitting about on the short grass.  When disturbed they would rise into the wind and make headway against it at ground level, doing about 15-20 mph except one bird who actually achieved a minus ground speed and slowly backed towards us.’

There is also a record of a flock of wood pigons (Columba palumbus) moving forward at 40 miles/h 64 km/h in the face of a 110 mile/h 177 km/h gale when they should have been moving backwards!  (McNabb, 1953).

Wood elsewhere gives the maximum speed of the eider duck (Somateria mollissima) as 30-35 mph 48-56 kmh, so the ducks in Meinertzhagen’s story were doing something north of three times their usual maximum air-speed.

Unfortunately, the reference corresponding with the McNabb 1953 citation is extremely uninformative: “McNabb, D (1953). Field (22 Feb).”  That’s it.  Anyone know what it means?

Anyway, my question is: this is complete nonsense, isn’t it?  Birds fly by pushing against the air, not the ground, so surely — surely — the only speed that matters is air-speed?

Am I missing something?  Is this possible?  Has it been documented under laboratory conditions?  Has it been observed in the wild other than by Meinertzhagen and McNabb?

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28 responses to “Can birds fly into a headwind that is faster than their own maximum speed?

  1. Maarten Daalder

    There was this ‘Faster Downwind Than The Wind’-car a little while ago, not sure if that’s a hoax or not (don’t have enough physics insight to properly verify that).

    This was the first link I could find:
    http://www.wired.com/autopia/2010/06/downwind-faster-than-the-wind/

  2. I would have to side with you on this one. Its all relative. So if the wind is blowing against the bird’s direction of travel its going to make the birds’ top speed relative to the ground slower by the same amount as the speed of the wind.

    Now it occurs to me that perhaps birds are able to do the same thing that sail boats do in order to travel into the wind, by flying diagonally or changing the direction of airflow over their wings to a more diagonal flow.

  3. Sure strikes me there is more at play –

    The air is impacting a solid surface and pushing at XX mph. But the birds are not presenting a _wall_, they’re presenting a nicely refined very small profile, so much of the pressure against them may just be slipping around them? (then again, physics is odd, but thats my first 1second thoguht about it.)

    Aerodynamicly, perhasp the shape of the wing itselfg is creating some backdraft or pocket of pressure that counters some of the wind pressureing towards them?

  4. I think they may do something with their wings that is something like a sailboat tacking into the wind. Studying the aerodynamics of these birds in a wind tunnel would definitely be interesting!

  5. Still air is very uniform, whereas I would imagine 90mph winds have far higher turbulence. I don’t know, but it seems plausible that (especially flocks of) birds might use this to their advantage.

  6. I agree with the “tacking” comments. I would also suggest that perhaps their “maximum” speed is not really all they are capable of doing, but only all they think they can do. They can probably go faster when they’re desperate.

  7. The McNabb 1953 reference does make sense once you appreciate that there’s a field-sports-based periodical called The Field, the issues of which are (or were) referred to by date, not by volume or issue number.

    As for the other stuff, meh. I will ask a colleague and get back to you.

    Darren

  8. “Big whorls have little whorls
    That feed on their velocity,
    And little whorls have lesser whorls
    And so on to viscosity.” — Lewis F Richardson

    There are some things in nature–well many thing in fact–that really do amaze me. For instance, it amazes me that all our bodys’ mitochondria come from our mother.

    Then there are things like this that are intended to amaze me, but instead, just mildly annoy me. I mean, yes it’d be great to figure out exactly what’s going on here with the birdies, but the real crux of the “magic” is just a person looking up at the intense wind and choosing to believe that what they’re seeing shouldn’t be possible.

    I agree with benwr‘s suggestion: I suspect a 90 mph wind has got a lot of turbulence. Have you ever checked out turbulence and just how crazy it is?

    How do you measure a bird’s max speed? What determines that? Are we talking about its max speed when gliding? It’s max speed when actively flapping? And is this a max speed measured from when the air isn’t moving at all?

    If the air was still, and the bird were flapping and gliding, then you could figure “terminal velocity”. I think it would be determined by how hard the bird can flap it’s wings and vs. how hard the air is pushing against the bird (drag). Of course the drag goes up the faster the bird goes so it’s complicated to actually calculate. But then the drag won’t be really high if the bird is directly into or directly against the wind because it won’t be presenting a large surface.

    Blowing wind happens in three dimensions. Turbulence is massively chaotic. And birds have been flying through air for a really long time. (Since Archaeopteryx?)

    If it is the case that some birds can fly into a 90 mpg headwind–never-mind what their max speed is supposed to be–then I am not surprised. Of course I also wouldn’t be surprised if a bird couldn’t fly into a 90 mph headwind. A system like that (really fast moving wind + bird flying into it) is really complex. I wouldn’t want to make any predictions on something like that. IMHO, that’s a time for scientists to do the other thing–observing. It’s not all about predictions all the time.


    Furry cows moo and decompress.

  9. Given how easy it seems for birds to hang in mid air when there’s a stiff wind, I would guess that due to their profile a N mph wind only moves them backwards at M mph, where M is a fairly small fraction of N.

  10. In remember reading that in older days when loggers used flumes for transporting timber, they would structure the bottom and sides of the flumes such that vortices would form and create enough push and pressure to allow transport of denser-than-water timber.

    Something similar is going on here, and it’s their aerodynamics that create vortices behind them that effectively push with a greater force than that of the wind against their sleak front.

  11. I’m no aerodynamics expert, although I have studied it a bit as a result of getting my pilot’s licence. I tend to agree that in a bird+air system, the only thing that matters to the bird is its forward speed relative to the air, so if the airflow is a smooth headwind, parallel to the ground, and moving faster than the bird can possibly fly forwards, the bird will move backwards relative to the ground.

    There are a few other possible factors that I can think of in the cited cases, and plenty of possible errors (n.b. I haven’t read through the source material, so I don’t know what they did or didn’t account for). How was the wind speed measured? Was is measured at ground level, or at the altitude of the birds? How was the maximum airspeed of the birds determined (e.g. under maximum wing-power they can generate, or maximum aerodynamic airspeed before they are damaged by the forces involved)?

    If the airflow is not parallel to the ground (e.g. if it was deflected upwards by a hill), there is the possibility that the birds could achieve positive ground speed in spite of the headwind due to the “tacking” effect that others have mentioned. If the airflow is hitting the bird from below, it can maintain altitude while effectively flying “downhill”, and the lift vector from its wings could even point partly forwards allowing it to achieve positive ground speed.

    Then again, I’m just guessing. :)

  12. I have to agree with everyone who said tacking. And just think, the birds can tack in all three dimensions.

  13. The basis of tacking is to have a grip on two media that are in relative motion. A sailboat has the sail in the air and the keel (the big vertical fin under the boat) in the water. The faster-than-the-wind propeller car has the propeller in the air and the wheels’ traction against the ground. The ice boat has the sail vs. the runners.

    The birds are only in contact with one medium. No tacking.

    Turbulence from the ground seems out because it would happen too fast for the bird to take advantage of. Ground effect seems out because any pressure from the bird would be blown behind it. Maybe the wind is just a lot slower very close to the ground?

    But the best and simplest explanation is that the guy is just wrong. The whole thing has that tall-tale feel.

    Hey, this is the first time I noticed the WordPress sign-in button, thanks for adding that.

  14. How about a logarithmic boundary layer? The stated wind speed would be at some fixed height above the ground – a fixed height because wind speed increases as you climb up through the boundary layer. The birds are doubtless low enough to be fighting less of a wind.

    Have you ever seen pelicans fly? Talk about in the boundary layer.

  15. Steve Witham notes: “The basis of tacking is to have a grip on two media that are in relative motion [...] The birds are only in contact with one medium. No tacking.” That sounds convincing to me.

    A couple of people have suggested that a 90 mph headwind will have a less-than-90 mph effect on birds, basically because they are small and aerodynamic and the wind will pass around them rather than catching them like a sail. No doubt this is correct so far as it goes, but remember that the birds don’t just need to hold their position in a headwind but actively push backwards against the air as it zips past at 90 mph.

    But lots of other interesting ideas here — keep ‘em coming.

  16. Another thought occurs to me, which inclines me more towards thinking that this is impossible, and that the reports are just mistakes. Whatever ideas have been proposed in this thread to explain birds’ supposed ability to fly into the wind — tacking, use of turbulence, etc. — would surely work just as well when flying in still air. A laminar 90mph airflow over a stationary (with respect to the ground) bird would surely produce exactly the same pattern of turbulence as the same bird moving at 90 mph through still air.

  17. I asked Colin Palmer, an engineer with a strong interest in the biomechanics of flight based at the University of Bristol, and he said…

    ———————–
    On the face of it, impossible. Once the bird is in the air and in steady flight, its frame of reference is the air it is flying in. It flies at a speed that is relative to the local air, so it moves with the air. If the bird is flying in the opposite direction to the moving air, then its ground speed will be bird speed – windspeed. So if the flight speed is less than the windspeed the bird goes backwards relative to the ground. If the bird cannot see (or in some other way sense) the ground it has no way to know that this is happening.

    Now, is it really that simple? There are a few possibilities that might have some effect, and one mentioned in the comments that will not. I will take that first.

    The sailboat analogy. Yes, sailboats (and ice yachts etc) can sail faster than the wind under certain conditions, which means that when tacking towards the wind they may be able to make progress that is a little faster than the oncoming wind. Birds cannot do this because it is necessary to cross the boundary between the two media of different densities – keel in the water and sails in the air. Birds are 100% in the air.

    Wind shear. The windspeed increases rapidly with height in the first 5 to 10 m, then the rate of increase reduces. So if the birds fly very low they may be able to fly within the slower air. Albatrosses make use of this wind shear to do dynamic soaring, where they build up speed in the region close to the surface then pull up into the higher wind region, which means hat for a short while their airspeed is higher than the steady state value and they gain height, but cannot see how this could be used to increase groundspeed into the wind for more than a few moments.

    So wind shear might explain “When disturbed they would rise into the wind and make headway against it at ground level…..”

    Turbulence. It is in theory possible to extract energy from turbulent air, and maybe birds can do it. However, it depends upon the scale of the turbulence relative to the size of the bird. If the ‘lumps’ of turbulence are large compared to the bird, then it just feels like regions of slower or faster air. So far as I am aware, turbulence is ‘large’ in that sense, so I think birds must have a hard time getting much out of it. An interesting area for study, but my gut tells me it is not the answer here.

    So, in summary I am very skeptical of the claims and keeping low in the wind shear seems the most plausible explanation.

    Colin

  18. Pingback: beatworm.co.uk » Blog Archive » Can birds fly into a headwind faster than their own maximum speed?

  19. When considering steady-state (sustained) situations, it’s basic Newtonian mechanics: the maximum airspeed is achieved when the drag equals the maximum thrust, and the drag is a function of airspeed, the shape of the object, the density and viscosity of the air, but most definitely not of the wind speed.

    The streamlined form of the bird is the same, and has the same constant effect on maximum airspeed, regardless of the wind speed. A bird flies faster than a flat plate with the same frontal area and thrust, but no explanation for the observations can be found in this fact.

    Alan is correct in his third paragraph: a flying object can exceed its maximum horizontal speed by following a trajectory through the air that is inclined downwards, as its weight then has a component in the direction of motion that acts in addition to the thrust. In still air this results in a descent, but if the wind velocity has an upwards component equal to the rate of that descent, the object follows a horizontal trajectory. A glider soaring on the wind blowing up a ridge is a special case of this, in which the only force opposing drag is the forwards component of its weight.

    My BOE calculations suggest that this cannot explain the size of the excess speeds reported. If these reports are substantially correct (and we are justified in being skeptical of them) then my guess is terrain-induced vorticity resulting in the observer and bird being subject to very different, and possibly opposing, local winds. Hills and ridges will often generate vortices in the airflow that are ‘anchored’ to the feature generating them and which can persist as long as the wind remains steady.They can also generate a stream of detached vortices travelling downwind, or a series of standing waves in the airflow which may extend many miles downwind, under which powerful vortices called rotors can form.

  20. I’m guessing not too many commenters live in the countryside! I’ve often seen birds fly against strong headwinds. I’ve also seen hawks and other predators *use* the headwind to help them get to their latest snack. Heck, more than once i’ve watched a hawk use a headwind to hover over a spot; I can only assume a tasty morsel was scampering around underneath it!

    Some birds do have a hard time flying into a strong wind; they’ll try different heights, some will tack, others will just give up and land on a nearby wire. But in general the only thing a strong wind does is slow them down!

    Don’t forget – a bird’s wings are not linear (unlike airplane wings); they are dynamic systems, so when one part of the wing is stalling, another part probably isn’t, allowing the bird to make progress. So they’re not actually pushing against the air – they’re manipulating the flow of it across their wings and body.

    You can also see this principle in fish swimming upstream, against a strong current. Salmon, going to their spawning grounds, come to mind. Cichlids in a fast moving tributary, and so on.

  21. Carolyn, no-one’s saying that birds can’t fly into a headwind. The specific claim in The Guinness Book of Animal Facts and Feats is much stronger: that they can fly into a headwind that is faster than the bird’s maximum speed and still make headway.

  22. It was late (for me) when I made my comment. :-) I just didn’t put that bit into my reply. It was in an edit – unusually, I actually edited my comment! – but it didn’t make it into the final version because I forgot.

    Just yesterday morning I saw a small group, not a flock just 4 or 5, predator birds (I think they were hawks, but I was wearing the wrong glasses) flying against the wind. The birds were making excellent westward progress against a very strong westerly wind.

    (Ain’t English grand? Westward: heading to the west; westerly: coming from the west…) :-)

    By manipulating the airflow across their wings, a bird can alter the relative velocity of the air, ensuring forward progress. The bird will be slower than normal, because of the extra drag caused by the wind, but it will still make progress. A butterfly, on the other hand? I’ve never seen them fly against a strong wind. They have relatively large, flat wings that can’t be manipulated very much. On the other hand, the Monarch butterfly flies south, to Mexico, and that has to be done against a persistently strong southerly wind.

    It’s all quite interesting! :-)

  23. Carolyn Ann’s comment contains a point that she probably didn’t mean to be taken literally, but is quite informative if you do. While a person walking against the wind experiences extra drag, a bird flying against the wind does not; the wind adds velocity (relative to the Earth), not drag (this is a vector addition, of course, and a headwind is of opposite sign to the airspeed, leading to a ground speed that is less than, or in the opposite direction to, the airspeed.) This is not just semantic nitpicking, as it explains why a person can walk against a wind that is much faster than she can run, while a bird cannot progress against a wind that is faster than the highest airspeed it can achieve.

    There is no magic in propulsion by wing-flapping, or the particular way that birds do it, that makes it possible for a bird to circumvent this fundamental physical principle. Butterflies cannot make progress against anything but breezes simply because they cannot fly very fast. The Monarchs’ migration is achieved by staying out of strong contrary winds, either by staying low, in the boundary layer, or not flying at all when that is too strong.

  24. As they say, all you can do is exploit wind speed differences… but don’t underestimate the power of that! Albatrosses fly fast, and google on:
    lisenby world record
    Check out the under-400mph videos; over that it’s pretty invisible. That was done by repeatedly accumulating the benefit of successive differences of about 65mph.
    And the GBWR was wrong.

  25. Well, I certainly underestimated it, in that I have been aware of dynamic soaring since Ingo Renner demonstrated it in a manned sailplane in 1974 (Albatrosses and perhaps pterodactyls had demonstrated it before then, of course), but I would never have guessed that the speeds shown here could be reached.

    I don’t know that it could explain the observations quoted by Mike, though, as it seems to require repeated reversals in direction (it also involves extreme g-forces at these speeds, if the instrumentation log on one of the pages is correctly calibrated.) I am wondering if there are situations in which the path can be straightened out, and I can think of a couple of cases where perhaps it could, at least to some extent: one is a helical or roller-coaster path along a wind gradient or horizontal vortex, and perhaps there’s a way of moving from vortex to vortex in a vortex sheet that could work.

    The Eider Duck case quoted by Mike is quite probably just a case of exploiting the boundary layer, with perhaps some help from the ground effect (wings are more efficient when within a fraction of their span from the surface).

  26. Personally, I’d ask “how was the ‘maximal speed’ measured”? Couldn’t the birds simply reserve their maximal speed for cases where they actually need it to move forwards, otherwise instinctively limiting themselves to more energy-intensive motion?

  27. Tommy de Vries

    Dear Sir,
    it is not that difficult.
    Ask any sailor and he can tell you why.

    Kind regards,
    Tommy de Vries

  28. Read the comments. The sailing analogy has been proposed, discussed and persuasively discounted.

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