The bird, its form and function

Front matter

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Contents

CHAPTER PAOB

II. FEATHERS 19

III. THE FRAMEWORK OF THE BIRD 62

Chapter I Ancestors

ITH the exception of Astronomy, the science which most powerfully dominates our imagination is Palaeontology, or the study of the life of bygone ages. Of all things in Nature, the stars symbolize absolute immensity, their distances stretching out beyond our utmost calculation. So the revelations of Palaeontology take us far beyond the sciences of life on the earth to-day, and open vistas of time reaching back more than five-hundred-fold the duration of the sway of mankind. Fossil bones — philosophically more precious than any jewels which Mother Earth has yielded — are the only certain clews to the restoration of the life of past ages, millions of years before the first being awakened into human consciousness from the sleep of the animal mind.

Until recently, Palaeontology has been popularly considered one of the dryest and most uninteresting of the 'ologies, but now that the fossil collections in our museums are being arranged so logically and so interestingly, the most casual lover of Nature can read as he runs some of the "poems hidden in the bones." As Professor Huxley once said, "Palaeontology is simply the biology of the past, and a fossil animal differs only in this regard from a stuffed one, that the one has been dead longer than the other, for ages instead of for days."

A great many more fossil mammals and reptiles have been discovered than birds, and the reason may perhaps be conjectured. The bones and bodies of birds were in former times as now very light, and if death occurred on the water, the body would float and probably be devoured by some aquatic reptile. Then, again, when some cataclysm of nature or change of climate obliterated whole herds and even races of terrestrial creatures, the birds would escape by flight, and when death eventually came, they would be stricken, not in flocks, but singly and in widely scattered places as to-day.

For perhaps a million years in the past, birds have changed scarcely at all, — the bones of this period belonging to the species or at least genera of living birds. But in the period known as the Cretaceous, when the gigantic Dinosaurs flourished and those flying reptile-dragons — the Pterodactyls— flapped through the air, a few remains of birds have been found. Some of these are so complete that almost perfect skeletons have been set up, enabling us vividly to imagine how the bird looked when swimming through the waters of our globe, or flying through the air, perhaps four millions of years ago.

The most remarkable peculiarity of these birds was the possession of teeth. Two of the most well-known examples are called Ichthyornis and Hesperornis. The bones of these birds were discovered by Professor Marsh imbedded in the rocks of western Kansas, and they are now preserved in the museum of Yale University. Professor Marsh tells us that Hesperornis, the Bird of the

FIG. 1. — Restored skeleton of Ichthyornis (after Marsh). 1/2 natural size.

West, "was a typical aquatic bird, and in habit was doubtless very similar to the loon, although, flight being impossible, its life was probably passed entirely upon the water, except when visiting the shore for the purpose of breeding. The nearest land at that time was the suecession of low islands which marked the position of the present Rocky Mountains. In the shallow tropical sea, extending from this land five hundred miles or more to the eastward, and to unknown limits north and south, there was the greatest abundance and variety of fishes, and these doubtless constituted the main food of the present species. Hesperornis, as we have seen, was an admirable diver; while the long neck, with its capabilities of rapid flexure, and the long slender jaws armed with sharp recurved teeth, formed together a perfect instrument for the capture and retention of the most agile fish. The lower jaws were united in front only by cartilage, as in serpents, and had on each side a joint which admitted of some motion, so the power of swallowing was doubtless equal to almost any emergency."

Hesperornis had numerous teeth set in grooves like those of serpents and crocodiles, but in Ichthyornis ('Fishbird/ so called because its vertebra? are biconcave like those of a fish) the teeth were in separate sockets as in alligators. The latter bird was not large, being about the size of a pigeon, and it had well-developed wings.

It is interesting to compare Hesperornis with the group of penguins, both being highly specialized, although in ways so different, for an almost wholly aquatic life. Hesperornis swam by strong strokes of its great webbed, or lobed, toes, its wings dangling uselessly for generation after generation, until all trace, save a vestigial humerus, of their bony support disappeared. Penguins, however, make but little use of their feet in swimming, only occasionally aiding the tail in steering; but they literally fly through the water by means of their flipper-like wings.

The large size of the leg and toe bones of Hesperornis shows that great speed was attainable in the water,

FIG. 2. — Lower jaw of Ichthyornis (after Marsh). 4/5 natural sizf.

FIG. 3.— Lower jaw of Alligator. 1/6 natural size. The teeth are set in distinct sockets both in the extinct bird and in the living reptile.

while only a single bone remained to show where the wings of its ancestors were situated. It is doubtful if it could stand erect upon land, being in this respect more helpless even than a grebe. Its nest, if it made one, must have been at the very edge of the shore, from which it could wriggle or push itself with its powerful toes into the water. The thought of the untold generations of birds which must have preceded this toothed, wingless, feathered being, makes the mind falter at the vast stretches of time during which evolution has been unceasingly at work.

When we examine the skull of Hesperornis we get a clew to the reason why this great creature, nearly as large as a man, succumbed when some slight change in its environment called for new adjustments in its habits of life. Its brain was comparatively smaller than that of any existing bird; and this absence of brain power implied a total lack of that ingenuity, so prominent in the crow, which, when man alters the face of the land, changes its habits, and with increasing wit holds its own against guns and traps.

When Hesperornis passed, it was succeeded by birds much smaller in size but of greater wit — loons and grebes —which hold their own even to the present day.

When in the depth of the winter, a full hundred miles from the nearest land, one sees a loon in the path of the steamer, listens to its weird, maniacal laughter, and sees it slowly sink downward through the green waters, it truly seems a hint of the bird-life of long-past ages.

We must now pass back, as nearly as can be estimated, over two millions of years, through the ages when the Iguanodonts and Megalosaurs lived, long before the first serpents had evolved and about the time when the first timid forerunners of the mammals made their appearance,— tiny insect-eating creatures which were fated to remain so long subordinate to the masterful giant reptiles. This was about the middle of the Jurassic period, and in deposits of this epoch have been found remains of the very first birds of which we know anything.

Two specimens have been discovered and named Archceopteryx (ancient-winged-creature). From these two little stone slabs, one in the British Museum and the other at Berlin, we know that these birds were about the size of a crow. Instead of the broad, fan-shaped tail of modern birds, the tail of the ArcJiceopteryx was a long, jointed affair like that of a lizard, and was fringed with large feathers — a pair growing from each of the twenty joints. The wings were not large, and instead of the fingers being concealed by feathers, there were three entirely free digits, each armed with a. claw, in front of each wing. The skin-covered jaws were furnished with teeth, but the feet and legs were much like those of an ordinary crow.

Taken all in all, this was a most wonderful discovery, linking birds and reptiles together, and proving beyond all dispute the fact of their common origin. Perhaps the most surprising fact was the remarkable development of the plumage of the wings and tail, showing that perfect feathers were in existence at least six millions of years ago.

In the rocks deposited in very ancient epochs are found many footprints which were supposed to be those of huge birds, but it is more probable that they were made by certain three-toed reptiles which, like birds, walked or hopped on two feet. Indeed Nature seems to have made several abortive attempts to produce birdlike creatures before she struck the right adjustments. Pterodactyls failed to become birds because they depended on a broad web of skin, like the wing of a bat, thus missing the all-necessary feather-ideal; Dinosaurs began at the wrong end, learning to stand on their hind feet and to hop, but never the delights of flight. These offshoots sooner or later were forced to the wall, but Archceopteryx seems to have been very near the true line of descent.

But after all, what a meagre record we have of the untold myriads of generations of birds which have succeeded each other through ages past! It is to be hoped that many more fossils may be discovered, for the hints given us in the anatomy of birds, and the glimpses of past history which flash out from the development of the chick within the egg, — all this evidence is becoming ever more and more clouded and illegible.

Having learned that birds are descended from a reptile-like ancestor, it is interesting to search among living reptiles for the one which most resembles birds, and we have no choice but to select the alligator — cold-blooded, scaly, bound to the earth though he is. A second near relation is to be found in the group of long-extinct Dinosaurs. A complete record of past ages would show the ancestral stems of alligators, Dinosaurs, and birds gradually approaching each other until somewhere, at some time, they were united in a common stock. But we must guard against the notion that birds are descended from any group of living reptiles; which is as fallacious an idea as that we Americans trace our direct descent from

FIG. 4. — Anhceopteryx preserved in the British Museum. The pelvic girdle, leg and tail show best in this specimen. 1/5 natural size.

io The Bird

the Chinese, or that mankind is descended from the chimpanzee or gorilla.

For the purpose of making more clear and interesting the ways in which birds have become especially adapted to their surroundings and needs, we may consider Archceopteryx as resembling closely the typical original birdtype from which all others have at least indirectly evolved ; and thus having obtained a definitely fixed starting-point, we may consider how some of the more representative birds of the present day came to acquire their widely differing structure and characteristics.*

The tree of evolution of reptiles may be compared to a growth where several great trunks spring from the ground close together, towering up separately but equally high; the topmost twigs of which are represented by the living species of serpents, turtles, lizards, and crocodiles respectively. A very different arboreal structure is presented in the genealogical tree of the Class of birds. Here, from a short trunk, we have many radiating branches, widely spreading and with thickly massed twigs, confusedly intermingled ; so slight are the divergences between adjoining groups and so equally do almost all share between them various reptilian characteristics.

It is not necessary to concern ourselves now with the processes of evolution, especially as scientists are still in doubt as to the exact methods. Let us read our Darwin, and hope for another, philosophically as great, to com-

* There are one or two reasons for regarding Archceopteryx as merely the tip of a parallel branch, but one sprouting close to the base of the avian tree.

FIG. 5. — Archoeopteryx preserved in the Berlin Museum. The skull, vertebrae, forelimbs and flight-feathers are remarkably distinct. 1/3 natural size.

plete the work, meanwhile adding our own mite of truthful observation to swell the whole, and help prepare the way for this other. For even Darwin's theory of evolution was but the consummation of theories of former years and centuries, — beginning with Thales and Anaximander, in the days of early Grecian civilization: indeed Aristotle, coming but two hundred years later, is the only name in the history of zoology worthy of a place with that of Darwin.

From the fragmentary evidence afforded by Archceopteryx we may conclude that this Bird of Old had a short, blunt, skinny bill of moderate size, furnished with teeth which would enable the owner to feed upon Jurassic berries and fruit, or more probably a carnivorous diet of lizards and insects. Its wings were weak, hinting that it was a flutterer rather than a true flyer, perhaps only scaling like a flying squirrel from the summit of one tree to the base of the next. Even this would give it an immense advantage over its terrestrial and arboreal non-flying enemies. The three free fingers on each wing would allow it to climb easily, to pry into crevices for insects, or to draw a berry-laden branch close to its bill.

Doubtless it frequently walked or ran on all fours, the more probably from its weak-loined condition, — the bones of the thigh-girdle not being fused together as in modern birds. Its tail has already been mentioned — a long double-feathered appendage, composed of a score of little vertebrae jointed together, — as we will later see the true forerunner of the modern fan-like tails. Its

FIG. 6. — Restoration of Archceopteryx (adapted from Smit). Notice the teeth, three fingers, and lizard-like tail.

H The Bird

feet and legs were little different from those of perching birds of to-day, with strong toes well adapted to cling to a branch. Finally, from a cast of the brain, which fortunately was found with one of the fossils, we know that, although small, it was that of a true quick-witted bird. As yet science has no more to tell us.

Our fancy may add an archaic attempt at song — a lizard's croak touched with the first harmony, which was to echo through all the ages to follow; we may also imagine, if we will, leathery eggs deposited in a rotten knot-hole of a Jurassic conifer.

In both islands of New Zealand well-preserved remains of giant birds have been discovered, to which has been given the name of moas. One species must have reached a height of ten or eleven feet, which would make it tower above the largest living ostrich. They were, in fact, not unrelated to these latter birds and, like them, were flightless (in some cases absolutely wingless), and they had great massive feet and legs. Native legends among the Maoris hint that these birds were in existence during the last few centuries before the coming of the white men.

In South America also, giant birds lived in ages past. One, the Phororhacos, stood seven to twelve feet in height, with a head and beak like that of a gigantic eagle. Unlike all eagles, however, this bird could not fly and doubtless ran down its prey, as a chicken runs down a grasshopper.

It is an interesting fact that in South America there lives to-day a bird known as the Seriema, which is probably at least an indirect descendant of the Phororhacos. The Seriema defies exact classification, sharing characters of cranes, bustards, and eagles. Its beak and inner claw are like those of a bird of prey, while in form of body, and in the other claws of the toes, and in the legs it is crane-like. One of these birds which I have observed for years in captivity is as gentle and as fearless as a bird can be. It will chase insects and field-mice outdoors in the Zoological Park, and will occasionally stalk solemnly into my office and, coming close to my desk, watch me closely. It has most beautiful grayblue eyes, with long eyelashes (Fig. 199), and if the birds of past ages were as comely and as lovable as this interesting species, I regret that only their fossil bones are left to us. As the Seriema runs down and kills a mouse, so the giant Phororhacos, doubtless, overtook and slew creatures as large as a deer. Its skull (Fig. 7) is drawn to the same scale as that of the living Seriema (Fig. 8).

The evolution which has gone on since these epochs of old, bringing into being the wonderfully varied forms of penguin, ostrich, albatross, peacock, and hummingbird, may be summed up in two words which it is well to know and remember, — Adaptive Radiation. This is the spreading out or radiating of bird-forms descended from the ancient stem, into all parts of the earth, each coming into contact with a particular environment, to adjust itself to which, its various organs and parts exercise different functions, until the friction of the "struggle for existence" has moulded each to its particular niche.

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If its lines lie in happy places, its race is established, and it pursues and flees, it fights and plays, it sings with joy or pants with fear, and Evolution marks another success in its inexorable movement onward and upward, — a new species is born!

Earth has few secrets from the birds. With wings and legs there is hardly a spot to which they cannot and indeed have not penetrated. Some find food and contentment in the desolate wastes of the far North; others spend almost all of their life on or above the sea far from

FIG. 7. — Skull of Phororhacos, drawn to scale with Fig. 8. 1/6 natural size.

land; thousands revel in the luxuriance of reeking tropical jungles; a lesser number are as perfectly suited to the blazing dust of the desert; and there are birds which burrow deep into the very earth itself. Day and night; heat and cold; water, earth, and air, have all been conquered by the thirteen or fourteen thousand species of birds which share the earth with us at the present day.

These brethren of ours, whose clans have so bravely conquered the dangers of millions of years, and at last have gained a foremost rank in the scale of living creatures, now find themselves face to face with the culminating effort of Nature, — Mankind. They cannot escape

FIG. 8. — Seriema, a living descendant of Phororachos , with characters of Cranes, Bustards, and Eagles. 1/6 natural size.

from us, though the least among them laughs to scorn our efforts at following through the air. Yet all must return sooner or later to earth for rest and food, and thus all are at our mercy.

Let us beware of needlessly destroying even one of the lives — so sublimely crowning the ages upon ages of evolving; and let us put forth all our efforts to save a threatened species from extinction; to give hearty aid to the last few individuals pitifully struggling to avoid absolute annihilation.

The beauty and genius of a work of art may be reconceived, though its first material expression be destroyed; a vanished harmony may yet again inspire the composer; but when the last individual of a race of living beings breathes no more, another heaven and another earth must pass before such a one can be again.

Chapter II

ANY definitions of the Class of birds have been given, but all fall short in some particular, or are weak in having exceptions. FEATHERED is the one word which always holds true. All birds have feathers, and nowhere else in the world are similar structures found. A feather, like an egg, is perfect in its adaptation to the bird's requirements, and also, like the egg, its structure is rather complicated.

Structure and Development

First let us look at the skin itself in which the feathers grow. To skin a bird is an easy matter, for the skin, or integument as it is called, is very slightly attached to the muscles underneath. The skin of a dove is almost like tissue-paper, and tears so easily that it is a marvel how the hundreds of feathers find a sufficiently strong attachment. Thin as is this skin, it is made up of three separate layers, but in order to make our feather-study enjoyable by not overburdening it with too many details, we will consider only the two more important layers of the skin — a deeper one, the dermis, and an outer, more

horny covering, the epidermis.

A list of all the structures of animals which are products of the outer layer alone would be a long and surprising one, and we would be very ready to grant the importance of skin. Such an enumeration would include all claws and talons, nails and teeth, the rattles of a snake, spurs, hairs, the scales of fishes and reptiles,

FIG. 9. — Tarpon-scale, shark-tooth, and peacock-feather; showing diversity of structure derived from the skin alone. 1/2 natural size.

spines, whalebone, beaks and feathers. Even the horn of a rhinocerus is only a solid mass of agglutinated hairs, while as the antithesis to this may be mentioned all down and feathers : the tiniest fluff from a hummingbird to the great pinion of a condor.

If we examine a newly hatched dove or sparrow, the little, ugly, sprawling creature, at first glance, seems to be entirely naked; but a closer inspection shows scanty tufts of down scattered irregularly over the body. This, like the set of milk-teeth in mammals, is useful only for a time, and is later pushed out by the second or true plumage. Even more numerous than the down-

FIG. 10. — Brown Pelican nestlings, showing feather papillae on body and wings.

About 1/4 natural size.

tufts are little pimples or dots, many hundreds of which cover certain parts of the skin. Each of these will eventually give rise to a perfect feather — quill, vane, barbs, and all.

The under layer of skin, or dermis, is very thin in birds, much more so than in reptiles and other animals.

The first intimation of the appearance of a feather, or of down, is shown by a thickened group, or pimple, of cells in this under layer of skin, which grows and presses upward toward the outer layer — the epidermis. This is exactly the way in which the scales of fishes and reptiles begin to form; and if, at this stage, the tiny projection should flatten out, the shining scale of a carp, the armor

FIG. 11. — Sprouting feathers of a 12-day embryo chick. Magnified 25 diameters.

of an alligator, or the cobble-scale of an iguana lizard might result. Indeed, in the feathers of a penguin we find transition stages of flat, almost unsplit feather-scales; while on the legs and feet of birds are reptile-like scales.

The evolution of scales, hair, and feathers is a most interesting problem, most of the details of which are beyond the scope of this work. Suffice it to say that in sharks, which are among the most primitive forms of fishes, the skin is covered with tiny denticles or spines, which consist of enamel and dentine, and which rest on small bony plates. This form of scale is the most ancient known, and the hint of teeth which the description conveys is not misleading; for we find that in some of these voracious fishes the spines in the skin become enlarged near the edge of the mouth, merging imperceptibly into the rows of cruel teeth which, to a certain extent, are homologous with the teeth of all higher animals. In other fishes the denticles become flattened scales, and many of these fish have teeth of corresponding platelike form. So it is interesting to know that the scales of fishes and reptiles, the feathers of birds, and the teeth of animals have all evolved from skin structures which at an early stage of growth bear considerable resemblance to each other.

But, in our young bird, the slender finger of cells which reaches upward, and whose base at the same time sinks deeply into the dermis, does not broaden out, but splits longitudinally into a number of folds, which gradually dry apart and harden into the slender, silky filaments which we know collectively as down.

At the base of, and in fact attached to, the little projection which gives rise to the nestling down is a small circular body of cells, which grows but little while the down plumage is serving its use; but when the bird is ready for a coat of true feathers this lower cellular mass begins to grow upward into a second finger, or column, of cells, pushing the base of the down feather out of its socket. This growth continuing, the down is lifted clear of the skin, being supported on the new structure, and

FIG. 12. — Early stages in the development of a down feather, showing close resemblance to scale of fish or reptile.

FIG. 12a. — Later stages of Fig. 12, showing the first splitting up of the

feather pulp.

soon brushed off and lost. Thus, little by little, in shreds and tatters, the baby plumage is shed and replaced by true feathers, which overlap, protecting the body from heat and cold, dust and rain.

FIG. 126. — Last stages in the formation of a down feather, showing the plumes well above the surface of the skin, as in a newly hatched chick. All greatly enlarged.

At the time of the first moult, this succession of feathers can be observed in almost any young bird, being more noticeable in large species, which have very thick or lengthened down, as gulls and ducks. A Red-winged Blackbird, or for that matter almost any passerine nestling, looks very odd when it rises up in the nest, gaping for food; the long gray streamers of down waving like an aureole around its head. In some water-birds this nestling down retains its usefulness for nearly two months.

FIG. 13. — Feather from the head of a young Bobolink, with down still attached to its tip. Twice natural size.

The feathers which replace the down are, when they first appear above the skin, rolled tightly and bound up in the thin tissue of the horny sheaths, so that they resemble a bundle of withes wrapped together in a cloth. In many young birds the feathers remain in this condition until they are nearly full grown, and a young cuckoo or kingfisher is a curious-looking object, most of the bird's body seeming to be tiled with small, bluish sticks.

FIG. 14. — Tip of feather from the crown of a young Song Sparrow, showing connection with down. Magnified 25 diameters.

FIG. 15. — Duck Hawk moulting into juvenal plumage, with the natal down coming away in shreds and tatters. 1/4 natural size.

When the folds of the developing feathers are sufficiently dry, they burst their sheaths and rapidly spread out.

The appearance of a young kingfisher or heron may be completely changed within a few hours time, so quickly and simultaneously does the first suit of feathers unroll.

The condition of young birds when hatched varies greatly in birds of different groups. Nestlings are, in many ways, like human babies, and there are as many differences in the one class as there are in the other,

FIG. 16. — Growth of an Ostrich feather from sheath to plume. 1/5 natural size.

between those from different countries, only Nature does for the little birds what parents do for the babies.

We see American babies wrapped in furs and blankets, wheeled in carriages, and rocked to sleep; while a tiny savage is strapped tightly to its mother's back, and as soon as possible allowed to run where it pleases, find its own toys and -develop its little muscles, gaining a degree of health and strength which many a civilized child would envy. So with birds, the highest — such as crows and thrushes — are hatched almost naked and must be warmed and cuddled and fed for many weeks, before they learn to take care of themselves; while birds lower in the scale — as our quail — are born covered thickly with down and with wings nearly feathered, and in a few days can fly and find their own food.

So a bird naked at birth is very helpless, one covered with down is more capable of taking care of itself, while

FIG. 17. — Nestling Kingfisher with feathers still in their sheaths. 2/3 natural size.

the few which are completely feathered when hatched may be said to have no chickhood except in the egg.

In the Crested Screamer (Fig. 264) the down-like character of the body-feathers of the adult birds may be a hint of the plumage of very ancient types of birds such as Archceopteryx.

Now we are ready to begin our study of the perfect feather itself, and we will, for once, have to disregard our rule of starting with the simpler form — the scale of

3° a reptile — and working up to a feather; for, if we except the down, there seems to be no connecting link left.

FIG. 18. — Young Brown Pelicans; hatched naked and helpless (altricial). 1/4 natural size.

FIG. 19. — Young Red Jungle Fowl one day old; hatched covered with down and able within a few hours to help itself (precocial). Almost natural size.