Re: "poor" fliers...

[Tommy Tyrberg <tommy.tyrberg@norrkoping.mail.telia.com>]

At 14:57 2000-02-03 -0600, you wrote:
>If you look at the figures, some of the *highest* relative pectoralis and
>supracoracoideus masses are found in the tinamiformes and galliformes, in
>which up to 25% of the entire body weight can be composed of just these two
>muscles. Comparable to what you see in pigeons, and various passeriformes
>(see Rayner's article 'Form and Function in Avian Flight' in _Current
>Ornithology 5_) So are these"weak" wings by any stretch of the imagination?
>       Think about the Wright Brothers for a moment, and compare them to
>gamebirds. Gamebirds, tinamous, pigeons, and some passeriformes are capable
>of vertical takeoffs. The Wright Brothers of course didn't use a vertical
>takeoff; in fact, it wasn't until Igor Sikorsky got the helicopter working
>(which I don't think began to be used extensively until after WWII, by
>which time the Germans had already got rockets and jet planes working) that
>we had an effective VTOL (vertical takeoff and landing) vehicle. And even
>today, successful VTOL aircraft aren't very common. The Soviets built one,
>and the British designed the Harrier jet; but the design specs for the new
>Joint Strike Fighter have actually tossed out the VTOL requirement in favor
>of STOVL (short take-off, vertical landing); and vertical anything is
>thrown out for the JSF Air Force variant to save on weight.
>       Why? Despite the fact that drag is minimal at low speeds, flying at
>low speeds is really expensive.
>       Lift is proportional not to speed, but speed *squared*- if you
>think about it, that explains why wingless aircraft like various weird NASA
>X-planes work- at supersonic speeds you can generate the necessary lift off
>just the fuselage alone. So you really have to flail those wings to produce
>enough lift to get off the ground from a standing start. Even a leap
>upwards only helps so much. So in order to use their predator-avoidance
>strategy of popping straight up and flying away, tinamous and fowl have to
>have an incredible amount of power. So I suspect that the reason a tinamou
>or ptarmigan will often run away from you instead of flying is that it's
>just a heck of a lot less work, even though they're easily capable of doing
>it.
>       Those animals with the least ability to flap the wings, the weakest
>powered fliers- actually, they have no flapping ability at all, because
>they aren't powered fliers- are the gliders. And they don't fly by popping
>straight up from a standing start on the ground, they climb off a tree and
>throw themselves off to get up sufficient airspeed to support body weight,
>they glide at relatively high speeds.
>       I guess at the highest end of the speed spectrum would be the ducks
>and pigeons, which also have a fair amount of wing muscle; they can take
>off  vertically but also can fly at very high speeds, where because of
>increasing drag, the power requirements again begin to increase.

Hmm... Not quite, pigeons are pretty fast, but the fastest fliers are the
raptors, who do it for a living, and birds with high wing-loadings, either
because they're heavy (Swans, and heavy ducks like the eider) or have small
wings (auks).  As to why they have so small wings, that's because they use
them both in air and water, so their size is a compromise to make the
usable in two media with very different densities. Swans are actually so
heavy that they have to fly at a speed below optimal cruise speed because
of insufficient muscle power. Note also that the power a muscle can output
in short burst, like takeoff, and in sustained flight is very different. If
You want to know more about the energetics and aerodynamics of flight I
strongly recommend:

Pennycuick, C. J.  1989. Bird flight performance: A Practical Calculation
Manual. OUP.

and

Hedenström, A. 1995. Ecology of Avian Flight. Lund.
  
>       Anyways, that's the sort of generalized- and hopefully, not too
>mangled- version of things. And as for galliformes in trees- well, wild
>turkeys do it, I believe they roost in trees at night. And is that chicken
>really that stupid? I mean, it flew, and it got up in a tree where a human
>couldn't get it. In the wild, that'd be exactly what you'd want to do.
>Okay, it's probably not a bright bird, but it's a darn sensible instinct.
>
>       -N
>
>As for small dinosaurs- I 'd note out that virtually all the small
>terrestrial dinosaurs fly. Only exception I can think of this is on islands
>(e.g. the Inaccessible Island Rail, Stephen's Island Wren?). This suggests
>to me not that dinosaurs are incapable of being small, but that they are
>excluded from doing so in the presence of mammalian competition, for
>whatever reason. Rodents, insectivores, possums, etc. are just better at
>this it seems.

There are (or rather was) a few more small flightless passerines, in
particular three more species of the same family as the Stephen Island Wren
(Acanthisittidae, no wrens) and an extinct sparrow (Emberiza alcoveri) from
the Canaries (a rather large sparrow though). None of them lasted long once
mammalian predators arrived, though the Stephen Island Wren persisted on
Stephen Island long after it became extinct on the Mainland of New Zealand,
until finally being exterminated by the Lighthouse-keepers cat in 1894.
Some species of the South American bird family Rhinocryptidae (Tapaculos or
Gallitos) are probably functionally flightless, at least nobody has ever
seen them fly, and the same may be true of a few other species who live in
the same habitat (on the ground in rainforest). These species are
quick-running and very good at concealment, tapaculos in particular being
extreme skulkers and very difficult to see (I know, I've tried).

Maintaining flight muscles and wings is very expensive, so generally birds
will lose flying ability very quickly (in evolutionary terms) if they no
longer need to fly to forage or escape predators. This is of corse
particularily common on islands, though unfortunately almost all these
flightless species have been exterminated by humans, directly or
indirectly. Dave Steadman estimates that the Polynesians alon have probably
accounted for more than 1,000 flightless bird species.

However most flightless species are medium size or large and there is a
definite tendency for flightless species to grow larger and heavier than
their volant ancestors. In general it seems that size tends to grow over
time in many lineages and flightless birds have much less reason to
restrict weight than volant species.

However there must be some special reason that flightless species with
weights <100 grams are almost non existant. One possible reason is that it
is very demanding to be small and warm-blooded, very small birds are
usually frantically busy feeding and may have insufficient mobility for
foraging if flightless (try to imagine a hummingbird WALKING from flower to
flower). The tapaculos I mentioned before probably succeed because they
live in what is probably the microclimatically least challenging
environment on earth (tropical rainforest understory) which also has a high
density of high-energy food (arthropods). The New Zealand "Wrens" also
lived in a maritime climate without extreme temperatures and in what was
apparently a very arthropod-rich environment until the Kiore (Polynesian
rat) arrived.
Another suggested reason is that insular (=small) populations of small
(=short-lived) birds are simply susceptible to extinction through natural
variations in numbers and therefore rare. The presence of small flightless
passerines on New Zealand which were the largest islands in the world
without mammalian predators may support this.

Perhaps the absence (rarity?) of VERY small dinosaurs is an argument for
warm-bloodedness? There are certainly many quite small ectothermic reptiles.

Tommy Tyrberg