CHAPTER IX.
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?
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.
_Cheltenham Press Ltd._ _Cheltenham and London._
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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.