One problem with that, as I see it, is that a weak bird ending up in the hardest position simply cannot sustain it if the strongest bird in the easiest position pushes the pace to its sustainable maximum. At some point, sooner or later, the weak bird will fall off from exhaustion. However, if it trails off from a certain position according to some rate of diminishing strength (rather than a sudden physiological failure), it alters the dynamics of the whole group and, as I hypothesize, effectively creates other optimal positions for other birds (if not itself) - thus a rotational pattern is induced such that somewhere in the process of the changing formation, the weak bird eventually finds itself in optimal or near optimal positions by which it can recover and sustain the average speed of the group. If the rotational dynamics work along principles like this, it is not a matter that the strongest bird can always simply muscle its way into the best position - there will be a continuous rotational dynamic, particularly if the bird in the easiest position becomes isolated because all the trailing birds begin to decelerate. Basically, I'm suggesting there are principles that drive a rotational dynamic - it may be that some birds spend more time in certain positions than others, but they will not be able to remain in those positions.
Hugh ----- Original Message ----- From: ERIC P. CHARLES To: Hugh Trenchard Cc: The Friday Morning Applied Complexity Coffee Group Sent: Monday, March 07, 2011 7:48 PM Subject: Re: [FRIAM] Birdies do the right thing! Alas, fundamental principles in animal behavior still tell us that animals should act selfishly. For selection to favor weakest individual willing to be in the hardest position, it only has to be the case that being in the hardest position in a group is still better than being alone. The reason we would expect the strongest individuals to be in the easiest positions is because they can move the weak individuals over. Selection should favor strong individuals who do not use their when they don't have to. The only conditions under which this arrangement should be violated is when the strongest individual gains a benefit from the weaker individual's presence. Only if this last condition is satisfied could selection favor strong individual willing to do the hardest job. Of course, if fighting is costly, this must be taken into account. Eric On Mon, Mar 7, 2011 10:00 PM, "Hugh Trenchard" <[email protected]> wrote: 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 -------------------------------------------------------------------------- ============================================================ 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 ============================================================ 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 Eric Charles Professional Student and Assistant Professor of Psychology Penn State University Altoona, PA 16601
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