http://friam.383.s1.nabble.com/Meeting-at-St-John-s-tomorrow-tp523290p523297.html
Thanks for all your comments. Next time I'm in Mexico, I will definitely do
my best to get some video footage. My recollection of what I saw in October
see, as you say. I can't remember how long the formations were stable -
dynamics involved. And after the formations broke down, they would often
different from the Cancun colonies I will need to investigate that.
something else to investigate). It seems, though, it is unlikely that a
migratory habits. So far, I still think the wind conditions are more likely
formations. As we all know, self-organized phenomena arise without leaders
different for frigatebirds. The formations must self-organize from some
physiological or energetic advantage to their coupling (ie. to their
universality of the "drafting principle" as I am calling it. I actually
point. But I suppose, at the very least, until I can get some good footage
to what I see. If anyone else is going, please keep an eye out for the
On the note about the decline of traveling geese, I really can't speculate.
formations going in all directions. But perhaps global warming is a factor
> Curious. I was wondering if, since the frigatebirds are aligning into
> formations without
> flapping, if it would be easier to perceive if there were differences in
> the "yaw" of the
> bird wing or body relative to its position in the formation. If so,
> several hypotheses
> about aerodynamics on formation might be arise. If, for example, there
> was a pronounced
> yaw to the right on the right side of the V due purely to the drafting
> aerodynamics of the
> V (this is just an example) then the bird in its local frame might be
> adjusting its position
> relative to the bird in front, which would be somewhat to the left of
> where it "should" be,
> (given the local aerodynamic properties of the surrounding air
> (temperature, pressure, wind speed, etc)
> so the bird would work harder to adjust its position so that the bird in
> front would be
> more in the expected position. At some point the energy advantage gained
> by remaining
> in the V formation would be lost, and the V would not be supportable.
>
> Frigatebirds are relatively large, so the idea here is that any drafting
> effect would not occur
> uniformly on any given bird in a V formation, possibly causing various
> local yaws and compensations.
>
> Carl
>
> Hugh Trenchard wrote:
>> I am a lurker on this listserv and find many of the discussions here
>> interesting and valuable. Recently I was in Mexico and noticed a couple
>> of
>> interesting complex phenomena I thought I would share with this group.
>>
>> The first relates to frigatebird formations and ties in with observations
>> of
>> these birds I made last year. Last year, when in Mazatlan, I noticed
>> that
>> frigatebirds often hover and glide for several minutes at a time without
>> flapping and that they tend to glide in disorderd configurations until
>> they
>> spontaneously undergo a phase change (it seems to me) when they align in
>> vee
>> formations - still gliding nonetheless. These are fantastic sights to
>> see,
>> since the birds seem to hang in the air in these vee formations without
>> passing across the sky at the relatively high speeds of geese, for
>> example.
>>
>> This year, in Cancun, I noticed frigatebirds gliding in disordered
>> configurations and, waiting patiently for the phase change, I was
>> disappointed when these changes did not occur. I wondered if I was
>> imagining the alignments I saw last year in Mazatlan, but fairly certain
>> I
>> wasn't, I speculate why the phase changes did not occur among the birds I
>> saw in Cancun. Firstly it's possible the frigatebird colonies on the
>> Caribbean side of Mexico simply don't undergo these formations, being a
>> slightly different sub-species or what have you. Perhaps, but I
>> hypothesize
>> that the wind speeds are the primary factor in determining whether
>> formation
>> phase changes occur.
>>
>> In Mazatlan last year in late Sept/early October, the wind speeds were
>> low,
>> I recall. In Cancun, wind speeds were significantly higher. I suggest
>> that
>> gliding in vee formations can only occur between a certain range of wind
>> speed - if wind speed is too low, the birds cannot glide at all; if too
>> high, they can glide, but they cannot align in vee formations. The
>> critical
>> range allows frigate birds to draft when gliding behind another while
>> maintaining position, but above the range the drafting effect is too high
>> and the birds get "sucked" through - or tend to fall, it looked to me -
>> the
>> low pressure areas and cannot hold their positions.
>>
>> Drafting ordinarily has the effect of saving energy (a la cyclists in a
>> peloton), but if birds are gliding and already saving substantial energy
>> by
>> not flapping their wings, I wondered whether any significant energy
>> savings
>> benefit can be derived by aligning in vee formations while gliding. At
>> first I thought not, but gliding inevitably requires some energy - small
>> muscle coordination and positional adjustments - not as costly as
>> flapping
>> wings, but some energy is required. When frigatebirds form vees, I
>> hypothesize there is in fact significant energy savings for those birds
>> in
>> drafting positions - small muscle contractions for positional adjustments
>> may be reduced, and birds in these formations will expend less energy.
>> They
>> would not, I suggest, align in these ways if it were not for some energy
>> savings benefit.
>>
>> Because frigatebirds do not generate the higher air pressure behind which
>> to
>> draft, such as geese do, or cyclists do, or fish in water do by
>> propelling
>> themselves through the medium (air or water), I suggest this form of
>> energy
>> savings constitutes a third type of "drafting". The other is energy
>> reduction by huddling, such as penguins undergo. So I suggest three
>> types
>> of drafting occurrences:
>>
>> I Occurs when system components generate effective air or
>> liquid pressure as they propel themselves through the medium; eg. cyclist
>> pelotons, fish schools, geese in vees;
>>
>> II Occurs when system components remain stationery and air
>> or
>> liquid pressure is generated externally; eg frigatebirds in vees while
>> gliding and remaining more or less positionally stable, and possibly some
>> types of fish (here I suggest this may occur in fish swimming upstream,
>> such
>> as salmon, which may hold themselves in a stationery position against the
>> flow of the water - I haven't specifically observed any interesting
>> drafting
>> formations as a result, although I have watched salmon swim upstream and
>> speculate drafting formations do occur)
>>
>> III Occurs when system components remain stationery and
>> environment temperature drops; eg. penguin huddles
>>
>> Type I exhibit phase changes from disordered states to ordered states and
>> back again through hysteresis loops. For cyclists, when peloton speeds
>> are
>> higher than a critical speed/drafting threshold, disorder in the peloton
>> occurs. In a peloton, density is generally higher at low speeds and
>> density
>> decreases as speeds increase. At a relatively high threshold speed, a
>> peloton loses cohesiveness entirely. To resume cohesion, peloton speeds
>> must fall to a lower threshold to resume cohesive formations (I've
>> observed
>> and documented this). The loop is clockwise (speed on Y axis,
>> density/order
>> on X) , but is the inverse of vehicle traffic hysteresis, for example,
>> where
>> density increases as speed decreases (note that drafting is not a factor
>> in
>> traffic).
>>
>> For frigatebirds, because order increases as windspeed increases to a
>> threshold range, above which disorder occurs, wind speeds must only drop
>> to
>> within the critical range for order to occur again. As a result the
>> hysteresis loop may not exist or is not as evident. I tentatively
>> speculate
>> this windspeed range is approximately equivalent to the magnitude of
>> drafting benefit derived when birds are in drafting formations; similarly
>> the height of the hysteresis loop in drafting cyclists is related to the
>> drafting benefit derived (but may not precisely match it).
>>
>> So drafting parameter seems to represent a constant that manifests itself
>> in
>> related but different ways. For example, in Type 1 situations, drafting
>> parameter indicates the magnitude of the hysteresis loop; in Type II
>> where
>> there is no hysteresis, drafting parameter indicates the magnitude of the
>> critical range of speeds within which certain formations occur. Drafting
>> parameter is thus also a general principle underlying the self-organized
>> complex behaviour of a number of different systems.
>>
>> For Type III (penguin huddles), density/order increases as temperature
>> drops
>> (requiring greater energy output to remain warm, so a decrease in
>> temperature is equivalent to an increase in speed in Type I situations);
>> density/order decreases as temperature increases to some threshold, after
>> which there is no huddle cohesion. Presumably at some very cold
>> temperature
>> the huddle cannot generate enough heat and disintegrates by penguins
>> freezing to death. In the direction of temperature increase, the
>> hysteresis
>> loop occurs when disorder occurs at a critical temperature, but must fall
>> to
>> some lower threshold temperature for the huddle to occur again.
>>
>> In any event there is a lot more analysis to be made, and I have more to
>> say
>> even now, but here are a few observations. Basically, my point is that
>> through my frigatebird observations, I've identified a third type of
>> drafting situation. I had already identified the peloton (which is
>> obvious
>> and well documented) and huddle situations (which is not as obvious and
>> not
>> well documented). _____________
>>
>> The second, slightly less rigourous observation I made when in Cancun was
>> a
>> clustering effect among cabs. In Cancun, and likely many parts of Mexico,
>> all cabs are required to be of the same colors, so they are all easy to
>> spot. There are also many, many cabs in Cancun - it appears about one in
>> six vehicles is a taxi.
>>
>> On the roads, it appeared to me that frequently cab clusters, or several
>> cabs near each other, would be driving within two degrees of each other,
>> often within one degree. One explanation is that they often originate in
>> the same location, many waiting at high person-density locations like the
>> airport, the bus station, etc. However, I am not sure this explains the
>> clustering on the roads, as cabs leaving from high density locations
>> would
>> not leave simultaneously when fares are widely distributed in time; they
>> also do not have the same destinations. So, clustering must be due to
>> something else, I think.
>>
>> Firstly, cab drivers tend to drive faster than the rest of the traffic,
>> especially when they have a fare on board. I am wondering if their fast
>> driving and deft abilities at weaving in and out of traffic allows them
>> to
>> agglomerate at stop lights. As traffic approaches stop lights, the
>> slower
>> driving traffic still leaves enough space for faster traffic further away
>> from the light to slip through and make up a few spaces, even as traffic
>> closest to the stop lights slow down and increase density. After a few
>> such
>> lights, faster traffic "sifts" through to the front, and ends up at the
>> front. This is just an idea, and no doubt there are a number of problems
>> with it (for example if cabs also tend to go through yellow and red
>> lights,
>> reducing agglomeration). Nonetheless, if the phenomenon is real - and I
>> observed it to occur more often than just chance would seem to explain -
>> then there must be a reason for it.
>>
>> In any event, I would be interested in any input others may have about
>> both
>> of these subjects.
>>
>>
>>
>>
>>
>>
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>>
>
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