I'm curious to know if there is much work showing the relative strengths of the
birds and their proportionate times spent in various positions. For example,
intuitively one might expect that weaker birds would actually take the easiest
positions for longer durations (contrary to the ornithologist's assumptions of
the day); conversely one might expect the weakest birds to be in the most
difficult positions for shorter durations than the stronger birds. I imagine
the rotational pattern to be counter-intuitive, at least counter-intuitive to
my understanding of peloton dynamics, since a weak bird in a hard position
can't simply accelerate to the easiest position at the apex - unlike a
weakening cyclist in the hardest position at the front, who can simply
decelerate and find a drafting position behind.
>From this one might imagine that flock rotation is more of a "backwards
>rotation" in which new effective apex positions are created farther back in
>the flock. These might be initiated by weaker birds behind the apex position,
>which due to weakening, gradually drop backward at some angle (perhaps) to its
>previous trajectory, and creates a new apex position for another bird (but not
>for the bird that started drifting back). One might imagine events in which
>such a drift backwards is lateral across to the opposite arm of the vee in
>order to avoid wing collision and/or some sort of other air instability. This
>might also create new or effective apex positions where a weaker bird may be
>able to recuperate. These adjustments behind the apex would also, one might
>imagine, force the bird in the previous apex position also to readjust
>position when the imbalance in uplift on either side begins to weaken it (if
>that happens).
In any event, I'm just throwing out some thoughts here and I would be
interested to know if there is much work on flock rotational dynamics (I
haven't seen much, but I haven't done an exhaustive search).
Hugh Trenchard
----- Original Message -----
From: [email protected]
To: [email protected]
Sent: Monday, March 07, 2011 12:59 PM
Subject: [FRIAM] Birdies do the right thing!
Yes, as always, Steve is correct. In my 1971 paper I included some stability
calculations indicating that for a flyer moving ahead of the Vee line things
became tougher, and vice versa.
The funny thing, as noted in that paper, was that the lead bird, at the apex
of the Vee, had the easiest job. This caused a lotta comment by ornithologists
who had observed that the lead position was normally assumed by the oldest and
senior bird. They asked, "Why would the strongest take the easiest job?". My
cynical answer was, "Twas ever thus, for Birds and Men!"
Peter Lissaman, Da Vinci Ventures
Expertise is not knowing everything, but knowing what to look for.
1454 Miracerros Loop South, Santa Fe, New Mexico 87505,USA
tel:(505)983-7728
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FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
lectures, archives, unsubscribe, maps at http://www.friam.org
