RE: Dromornithids and size limits.

["Jaime A. Headden" <qilongia@yahoo.com>]

Eric Martichuski (herewiss13@hotmail.com) wrote:

<You will note that none of the birds I've mentioned are known for their 
manual dexterity (so to speak).  If you can't anchor yourself to a limb,
it's rather awkward to stand on one leg while using the other to fiddle
with something.  Any task best suited to _two limbs_ (even if they are 
undexterous) gets really tricky.>

  Some birds do precisely that, standing on one leg and using the other to
play with things. However, parrots and turacos are birds that are
effectively three-legged climbers, in that they use their beaks to
manipulate and clamb with. Many corvoids and parrots use tools held in the
beak. Hoatzin and likely many early, manually-clawed birds climb
quadrupedally.

  Yes, it is true that birds cannot manipulate with the _wings_ but this
does not mean they cannot manipulate. One must think that in a
constraint-based system, animals adapt; it becomes neccessary to include
atypical abilities as part of the "manipulatory" arsenal, and not restrict
bird manipulation because they can use their hands, but mammals can. Birds
sacrified the relatively easy manipulation for the ability to locomote
exceptionally. Bird ancestors couldn't really pronate the limbs to begin
with, so that's not a major loss, but they managed to do just well without
being able to dribble a basketball. Meanwhile, they developed tripodal
stances with the tail as a prop, or with the beak acting as a "foot" for
climbing or holding tools, something no other mammals but primates can do,
and birds do it in MANY instances (tool use in primates are restricted to
some lemurs and apes, for the most part --- though I think I missed a
monkey or two).

<A degenerate wing will not easily turn into a clawed prey grasping limb 
(i.e. cats), a limb for becoming arboreal again (i.e. squirrels, primates,
 prosimians, etc. etc.), a general manipulator (i.e. racoons, beavers,
etc.  as mentioned above) or a burrowing limb (i.e. gophers, moles, prarie
dogs).>

  Need not be. Birds that need to manipulate develop a means, usually in
the head. Birds that have to tear simply grab hold of it, snap in a beak,
and shread. Meanwhile, larger birds like phorusrhacoids have HUGE heads
for rending, eagles have large beaks and bodies designed to tear apart a
large prey, falcons slam into their victims at velocities that shatter
prey bone. There are always means. This is not counting the pedal
variability and flexibility that give many birds a major advantage;
squirrels can rotate their ankles to some extent sideways, and bats
developed a reversed foot, whereas birds have eleutherodactyly,
zygodactly, pamprodactyly, lobiform ectaxonic digits, talons, and so
forth. Neither should be considered better than the other. Birds do it in
a different way.

<While many birds do scratch out burrows or hollows, they don't fill any 
exclusively (or even semi-exclusively) subterranean niches.  Any attempt
for them to do so would likely fail because they cannot specialize for the
task  as well as a burrowing mammal.>

  This may have more to do with that fact that nearly ALL birds that do
live in or make burrows of any sort still fly. If they were to lose
flight, for instance, and specialize as fossorial, it is likely that they,
like insects, mammals, lizards, snakes, and some fish do today would
specialize for it. The need to specialize for burrowing is, to a point,
unneccesary.

  Note that for their niches, birds and mammals are virtually exclusive,
and I've made this point before, but it bears repeating here: bats are the
only truly capable fliers in mammal history as we know it. Non-flapping
"flyers" like the various "gliding" squirrels, sugar glidersd,
dermopterans, or leaping primates like sifaka, do not represent threats to
niches held by birds. On the obverse, no mammalian terrestrial niche has
been exploited by a bird; highly cursorial birds are large and occur in
areas where cursorial mammals are relatively few and small, as in
ostriches and cheetahs not really being mutual competitors in Africa. No
mammal niche is threatened by birds. There will unlikely be, without a
vacuum, a "woolly" ostrich of some proportion and meat stock, a soaring,
taloned ferret, or giant trampling earth moving owls. No mammal/bird
competition in one niche truly has any exaptive argument that cannot be
reversed to say the same in the other way, ot basically: to our knowlegde
of their biology and natural history, there is no evidence that either
birds and bats are  so much better than the other in their niches that
they led to their superiority over the other in the niches that they are
in, currently. Bats are not simply better than birds at night (look at
owls) and birds are not better pollinators (many microbats are
nectarivorous specializers). Some niches are "duh" niches, like
fossoriality, until at such a point that there is a vacuum and a
neccessity to specialize. Penguins and seals do not compete and are
therefore not in conflict for specialization. And the list goes on.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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