There was a report in The Age a couple of days ago (
http://www.theage.com.au/world/science/natures-amazing-synchrony-explained-20111115-1ngiq.html)
on shoal behaviour in fish - basically they seem to work on avoiding the
closest fish and trying to get near the most distant ones. I wonder if bird
flocks are similar in terms of sticking together and avoiding collisions?
On 16 November 2011 10:27, Tony Russel <> wrote:
> I'm not convinced that wing pressure has anything to do with flocking.
> Birds flock for reasons of safety in numbers from predators, just as many
> other animals do, and maybe some birds/animals are simply gregarious. All
> those wings flapping out of synch would self cancel any cumulative effect
> on
> air pressure.
>
> Tony
>
> -----Original Message-----
> From:
> On Behalf Of David James
> Sent: Tuesday, 15 November 2011 3:04 PM
> To:
> Subject: Re: [Birding-Aus] Wing pressure
>
> Following from Philip's interpretation I would make the following
> prediction:
>
> If the primary purpose (or a major benefit) of flocking tightly was to get
> lift and save energy during take off, you would expect to see clear
> evidence
> of birds clustering and positioning prior to take off (not when a predator
> arrives, but perhaps when shifting locations or changing behaviours). Maybe
> there is clear evidence of this, but i can't recall seeing it.
>
> David James,
> Sydney
>
> ==============================
>
>
> ________________________________
> _______________________________
> From:
> on behalf of Philip Veerman
>
> Sent: 14 November 2011 21:34
> To: 'Pat OMalley';
> Subject: Re: [Birding-Aus] Wing pressure
>
> Curious question. I reckon the reason why a flock of birds take off all
> very close together, is due entirely to that they were perched very
> close together (e.g. on a high tide roost site for waders or ducks etc
> or on limited perches (powerlines etc) and they are all responding to
> the same stimulus to fly (such as a predator or rising water levels).
> Combined with the fact that if it is a predator causing the movement, it
> is likely to be bad to be the last one left standing.
>
> There could of course be something in the explanation given below that
> appears sensible and maybe adds something to the issue but it is hard to
> imagine that the reason is anything other than that it is a logical
> consequence of that they were perched together and fly off in response
> to the same stimulus. Part of the reason of perching together e.g.
> hundreds of waders huddled on a mudflat is that the birds in the middle
> are less exposed to predators.
>
> As to how they avoid injury, an interesting thing. They see, think and
> react very fast.
>
> Philip
>
> -----Original Message-----
> From:
> On Behalf Of Pat
> OMalley
> Sent: Monday, 14 November 2011 8:55 PM
> To:
> Subject: [Birding-Aus] Wing pressure
>
>
> Hi all,
>
> I've been sent the following for comment. can anyone enlighten me (and
> thus my physicist friend)?
>
> Best
>
> Pat
>
>
> It occurred to me while watching a flock of birds take off that they
> were doing it in a manner conducive to injury: they were all very close
> together, and three dimensionally so. Why would they do this? Here is
> the answer, I think.
>
> There has been, of course a lot of study and modelling of flocking and
> schooling (fish) and so on, but in my brief perusal of the literature,
> viz., I googled <bird flocking>, I saw no reference to the following:
>
> Birds expend a lot of energy taking off. Some big birds have adopted
> take-off strategies like running to increase lift and so on. So, let's
> first model a bird wing very badly, but sufficiently for our purposes,
> by an umbrella: on the up stroke the umbrella collapses, and although
> there will be drag, and a slight increase in pressure above the
> umbrella, compared to the down stroke, wherein the umbrella opens up,
> this will be a lot less. Hence the lift. Now, one bird taking off
> (vertically, for simplicity) will be flapping downwards against normal
> atmospheric pressure, and the pressure will locally increase during the
> downstroke. But because the air is free to move sideways, the increase
> in pressure will be limited. If, however, we have a hundred birds
> tightly arranged in a circular area, the pressure increase, particularly
> towards the center of the flock, will be greatly increased, since the
> air can only move sideways at the perimeter of the circle. This will
> result in increased lift for most of the birds (actually for all the
> birds, since the ones at the perimeter will still benefit from some
> pressure increase) for the same energy expenditure.
>
> The above argument works a fortiori for a three dimensional flock.
>
> Let me know what you think.
>
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