Flightless Birds.
"And first, I praise the nobler traits
Of birds preceding Noah,
The giant clan, whose meat was Man,
Dinornis, Apteryx, Moa."--_Courthope._
The steamer duck--The owl parrot--the flightless grebe of
Titicaca--The dodo and solitaire--The ostrich tribe--The penguin's
wings.
The poet who penned the above lines thought
more of rhymes than of reasons--as Poets so often do. What were their
"nobler traits"? He omits to mention them. None of them were ever
carnivorous: and the Apteryx could by no stretch of the imagination be
called a "giant." The one outstanding feature which does distinguish
these birds he fails entirely to appreciate--and this is their
flightless condition.
A flightless bird is an anomaly. Yet there are some who profess to
believe that this state affords us an insight into the early stages
of the Evolution of the wing. As a matter of fact it demonstrates the
exact opposite--its degeneration.
How is it that birds ever came to such a pass? A study of living
flightless birds, and birds that are well on the way to this condition,
will afford us a ready answer.
Whenever we find birds living, so to speak, lives of languorous
ease--where there are no enemies to be evaded, where there is an
abundance of food to be picked up on the ground all the year round,
and the climate is kindly, there flight is no longer practised. Year
by year, generation after generation passes by, and no use whatever
is made of the wings. In all such cases these once most vital organs
dwindle away, and finally vanish. We can trace every step in this
process of decay.
We may begin with the "steamer-duck" of the Falklands. In this species,
after the first moult, the power of flight is lost for ever. Among
living birds only a few species, apart from the ostrich-tribe, are
in this dolorous case. The owl-parrot, or kakapo, of New Zealand, is
one of these. A grebe found only on Lake Titacaca, perched high up a
mountain-side is another. In both these birds the keel of the sternum
is represented by the merest vestige, the breast-bone being reduced to
the condition found in the ostrich-tribe.
The two giant pigeons, the dodo, and its cousin the solitaire, afford
instances where the loss of flight has been followed by extinction;
owing to the invasion of their haunts, through the agency of man, by
pigs and other domesticated animals, which destroyed their eggs and
young.
The ostrich-tribe is peculiarly interesting: owing to the fact that
their wings present a really wonderful series of degenerating stages.
The wings of all differ conspicuously from those of other birds in the
great length and looseness of the texture of the feathers. Those of the
African ostrich are the largest of all; but they are quite useless for
the purpose of flight, though they are used as aids in running. In the
South American ostrich, or rhea, they are also large, but again useless
for flight, for the "quill-feathers" are very weak, and have no "web,"
such as one finds in the quills of flying birds. And besides, the
muscles of the wing have degenerated, the breast-muscles having become
reduced to mere vestiges.
In both the African and South American ostriches, the skeleton of
the wing, compared with, that, say, of a swan, would seem, to the
inexpert, to be quite normal. But with the cassowary, the emu, or the
apteryx matters are very different. Here, at the first glance, it is
apparent that the process of decay is far advanced; for the bones of
the hand have, as it were, shrunk up, so that a mere stump is all that
remains. The wing of the cassowary is further remarkable for the fact
that some of the fore-arm quills, or "secondaries" are represented
by long, stiff quills, resembling spines of a porcupine; the "vane"
of the feather, which normally runs down each side of the shaft, has
vanished altogether. What part they play in the bird's life history it
is impossible to say. They certainly cannot be used as weapons, and
they as certainly are not "ornaments." In the extinct moas the wing had
still further degenerated. In some species no more than a stump of
the upper arm bone was left, and in others not only this, but even the
shoulder-girdle had vanished, so that only one pair of limbs remained.
Another remarkable flightless bird is the penguin. Here the wing has
changed its form to assume that of a paddle; superficially identical
with that of the whale, or the turtle, or that of the extinct
sea-dragon ichthyosaurus. These paddles have been "re-modelled," so
to speak, to enable them to be used for what we may call flight under
water. Most birds which swim under water use the legs for propelling
the body: but the penguin uses his paddles instead. The paddle of the
turtle has similarly evolved out of a fore-leg used for walking on
land. The common tortoise may be taken as the type of this leg. In the
river, and pond-tortoises, the stumpy foot of the land-tortoise gives
place to a broad, webbed foot. In the turtles this webbed foot gives
place to the paddle.
After what has been said about the penguin it is instructive to turn
to the wings of the auk-tribe--the guillemot, razor-bill, and puffin.
These are very efficient for normal flight, but they are equally
efficient for use under water. For these birds swim as penguins do,
when submerged. Why then, did the penguin suffer the loss of the use of
his wings for flight?
[Illustration:
Cassowary. Penguin.
Ostrich. Kiwi.
]
This question leads to another. Why did that giant razor-bill known as
the great auk become flightless? It would seem that its wings somehow
failed to keep pace with the growth of its body, so that while they
remained sufficient for flight under water, they became useless for
flight in the air. Its failure in this led to its extinction, for
it was unable to escape from its arch-enemy man. When the old-time
sailors, somewhere about one hundred years ago, discovered its haunts
in Iceland could be profitably invaded for the purpose of collecting
feathers, and bait, they speedily wiped out the race; for being
flightless they were unable to escape the marauders once they had
effected a landing. Unhappily there was no Bird Protection Society in
those days, to stop this senseless slaughter.
Here our survey of Birds on the Wing ends. It began with flight through
the air, it ends with flight through the water. It is not a little
surprising, surely, to find that the same wing can be efficiently
used for both these extremes of motion. And still more surprising to
find that, this being so, the penguin should have been forced, so to
speak, to adopt the expedient of evolving a paddle; and so forego
the power of aerial locomotion. The skeleton of this wing, it was
pointed out, differed in no essential from that of the typical avian
wing. In some points, however, it has changed conspicuously. For
the bones have become greatly flattened, and the several parts of
the wing--arm, fore-arm, and hand--can no longer be bent upon one
another in the Z-shaped fashion of normal wings, while the "quill" or
"flight-feathers" have been reduced to so small a size that they are
unrecognizable.
[Illustration: Vultures.]
_Cheltenham Press Ltd._
_Cheltenham and London._
* * * * *
Transcriber's Note
All obvious typos were corrected and hyphenization was standardized.
The italic labels on the illustration facing page 102 were standardized
to match the other illustration's text. Illustrations were repositioned
so that paragraphs were not split.