"poor" fliers...

[Nick Longrich <nrlongri@midway.uchicago.edu>]

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.
        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.