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. > > > > > > > ============================================================ > 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
