BEFORE proceeding with the anatomy, a few words upon the flight of birds will not be out of place. The first points to be recognised are that the bird is heavier than air, and, therefore, the force of gravitation drawing the body down to earth comes into play. The bird does not master the force of gravitation by mere muscular power, but by a marvellous system of planes, which enable it to float upon the currents of air.
It is obvious that if a bird is to support itself by the downward blow of the wings upon the air, it must at the end of each downward stroke lift the wings upwards again, so as to prepare for the next downward movement. But each upward stroke would be in danger of neutralising the effect of the downward stroke were it not for two things—the overlap of the feathers and the convex and concave surfaces of the wings. The enormous difference this makes may be gathered if one considers the effect upon an umbrella by the wind. If the under or concave surface is exposed to the wind, the resistance is enormous as compared to the bulging or convex side, and, in a similar manner, the effort to lower the wing of a bird is so much greater as compared to the upward stroke when one realises that the wing of a bird is convex upon the upper surface and concave below. This fact is commonly overlooked by the student and painter of birds, with the result that a considerable portion of the beauty of the bird is unappreciated, namely the graceful lines of the wing (Plate xxiv).
Again, it will be noticed that the quill of the principal flight feathers is not placed exactly in the centre, and in overlapping the broader section will always be found to be underneath (Plate xxv). During a downward stroke of the wing the broad section will be pressed tightly against the narrow section of the feather above it, making one complete surface, and the passage of the air along this enables the bird to rise. The upward stroke, however, does not nullify this by bringing the bird down again, because the broad section of the feather is now unsupported and allows a certain quantity of the air to pass through the wing. Thus the muscular power of the downward stroke being so much greater almost all the muscles of flight upon a bird will be found upon the under surface of the body.
By means of the broad ligament at the base of the quills, the flight feathers can be turned at an angle in a manner similar to a Venetian blind. The action of soaring is practically that of sliding down the air until by closing the planes it once more rises, without effort, the air rushing under the convex wing.
The body of a bird is not covered thickly with feathers growing evenly from the skin. With but one or two exceptions all birds have large, bare tracts or spaces, from which feathers do not grow ; these tracts in many cases, being nearly equal in the aggregate area to the feathered tracts (Plate xxvx). They are known as Apteria, or naked tracts, and Pterylae, or feather tracts. The feathers themselves vary in size and form upon each tract, and it is due to these spaces that the various movements of the bird do not cause a wrinkling or cracking of the feathers, such as is found amongst the animals.
During life the naked tracts are not visible, being covered by the overlapping feathers, but their importance to the artist lies in the fact that the groups can be clearly followed in the plumage, giving a surface modelling to what otherwise would be a globular mass of feathers.
STUDIES OF FEATHERS WINGS OF A PARTRIDGE
The sculptor, for example, by a proper appreciation of these masses, can suggest the feathering although unable to avail himself of colour or pattern, and the designer, when treating a bird in a conventional manner, can work to a clearly defined plan instead of letting the pattern become a matter of chance.
These tracts vary slightly in size and shape in different birds, but the main arrangement is all that is necessary to the artist.
Although the bones of a bird correspond to those of mankind and animals, a closer examination will show that many of them are more or less soldered together, making one solid framework, whilst others have increased in numbers. To the artist, the skull of a bird is not a complex structure, the greater portion of it being taken up by the huge eye cavity (Plate xxvi).
This is hardly to be wondered at when it is realised that a bird depends almost for its very existence upon its sight, either for safety or food. In connection with this, it is interesting to note that nearly all birds of prey have the eyes placed well in front of the skull, whilst those that are preyed upon have them placed on either side where they can see all round them. Compare the Hawk or the Owl with a Pigeon or a Sparrow, and the same rule, when applied to animals, the Rabbit and the Mouse, compared to the Cat and the Fox. The eye of a bird is perfectly round and is usually black, encircled by a highly coloured iris, which contracts or enlarges at will.
FEATHER TRACTS OF BIRDS
The faculty of focus adjustment is very highly developed to accommodate the almost instantaneous changes of vision. A Hawk soaring like a speck in the blue sky minutely watching every movement upon the earth below, makes his deadly plunge with unerring aim. A Woodcock avoids every obstacle in the thickest coppice whilst travelling at a tremendous speed, and a Pigeon or a Sparrow whilst pecking up the crumbs from the ground, can watch every possessed by the bird alone is the neck farther round than is possible animals. This faculty is owing to the base of the skull will be found a into the first vertebrz of the neck movement of the prowling cat or overhead hawk. The eye of the Owl is specially adapted for nocturnal use ; the radiation of the feathers and the series of bony plates concentrating the vision, although, in addition, this bird possesses a very acute sense of hearing.
FEATHERS OF A PIGEON
The bird has three eyelids, upper and lower and nictitating membrane. When sleepy, the lower eyelid almost covers the eyeball, in contrast to the human eye wherein the upper lid possesses the greater movement, but when winking the bird draws the nictitating membrance across the eyeball. This membrane, or third lid, is semi-transparent and dilutes the intense glare whilst enabling it to see plainly, and is undoubtedly made use of when facing the light of the sun.
SKELETON OF A PIGEON
Another safeguard guard possessed by the bird alone is the power of turning the neck farther around than is possible in either mankind or animals. This faculty is owing to two causes – firstly, at the base of the skull will be found a small knob which fits into the first vertebrae of the neck and serves as a single pivot, whilst all other animals possess two projections, one on either side ; and secondly, the increase in the number of Cervide Vertebra (Plate xxvi). The long neck of the Giraffe only contains seven neck-bones, whilst the Sparrow possesses fourteen, and the Swan as many as twenty-three, and this flexibility on the part of the bird enables it to reach any part of its plumage. The remainder of the Vertebra on the contrary have become fused in such a manner as to be practically one bone, with corresponding lack of movement. In a bird almost the entire muscular power is devoted to the powers of flight, and as the greater the muscle the more powerful must be the bone to which it attaches, consequently we find a considerable increase in the size of the bones to which the wing muscles are attached. The great flight muscles, or Pectoral muscles, form the breast, and these lie on either side of a strong keel dividing the Sternum or breastbone. The shape of the keel varies in nearly every species of bird, having the greatest development in those of powerful flight, whilst in those who have lost the use of their wings the keel has disappeared entirely, and the Sternum is a flat plate, similar to that of the human skeleton. Many powerful birds of flight do not, however, use an extraordinary amount of muscular power. They soar and float upon the air currents, making use of the feathers of the wing to act as a series of planes, and the gulls and the Albatross have comparatively small keels to the Sternum by comparison with a Pigeon, and the latter again is small compared to that of a Humming Bird. The movement of the wings of this small bird is so fast that they appear to be transparent, and it has been estimated that they make from 1oo to 1,000 strokes of the wing per minute, developing more muscular energy than any other animal.
FIG 31. WING OF A BIRD / FIG 32. ARM OF A MAN
SKELETON OF A WILD DUCK IN FLIGHT
It will be noted that the Sternum of animals is attached to the ribs only. In the bird, these latter have been strengthened by a bony projection from each rib overlapping the next behind it, forming a kind of basket work. Even so, the constant pressure of the chest muscles during flight are apt to cause undue contraction were it not for the additional support given by a stout column of bone called the Coracoid Bone. Attached to this again is the Clavicle, better known as the Merrythought. It will thus be found that the shoulder of a bird has two bones which are not present in animals, whilst the Scapula, or shoulde-blade itself, takes a very secondary place, being the long knifelike bone lying alongside the Dorsal Vertebra.
WING OF A WILD DUCK.
The similarity between the wing of a bird and the arm of a man is very marked (Figs. 31 and 32), the greatest change taking place at the wrist where two bones take the place of eight. The fourth and fifth fingers have also disappeared, so that the bird has the first and second finger joined together, and a vestige of the thumb.
The Ilium, Iscbium, and Pubis have become fused into one bone, along with the vertebra ; and the Femur bone of the leg is relatively short. The knee proper of a bird is seldom visible, even in such long-legged birds as Herons and Flamingos, where the extra length is due to the elon-gation of the next two joints, the Tibia and the Tarsus. The so-called knee of a bird is actually the heel, and the Tarsus bones have become merged into one shank covered with scales.
In the foot, the great toe has turned backward, and the small toe has completely disappeared—the bird thus walking upon its toes and not upon the flat of the foot as in mankind.
The large feathers of the wing with slightly tapering ends are the Primaries, or first flight feathers, and those with broad ends are the Secondaries.
Although apparently very complicated, the arrangement of feathers on a wing is quite easy to follow.
The first Primary feather grows from the first joint, extending as a continuation of that bone. From the second bone, two Primary feathers grow, and from the next bone either seven, eight, or nine.
The Secondaries grow from the Radius, and average about fourteen in the smaller birds. These are always known as the flight feathers of a wing.
NOTE. --Primaries (Plate xxviii) vary but little in number, usually nine, ten, or eleven. Secondaries on the contrary vary considerably. In such birds wherein the wing is greatly lengthened it is the Secondaries which are increased in numbers, the two extremes being the Humming Bird with ten Primaries and six Secondaries, and the Albatross, with ten Primaries and forty Secondaries.
Plate XXIX. UNDERSIDE OF THE WING OF A WILD DUCK.
SKELETON OF A WILD DUCK IN FLIGHT
It is obvious that if these flight feathers were not supported in some manner, the pressure of air in a stroke of the wing would cause them to bend at the base of the quill. This is safeguarded against by a broad ligament, through which the quills pass, helping to keep the feathers in position, and again by a second row of stiff feathers, reaching about half way. They grow immediately over the flight feathers, so dose that the two seem to have grown together and attach to the same ligament. Consequently, they are identical in numbers to the feathers they cover, and are known as the Greater Coverts, the under surface of the wing being supported in the same manner. Overlapping these again will be found the Lesser Coverts, usually about Eve rows, each row reversing in direction.
NOTE—A peculiarity about the smaller song-birds is that they seldom have more than three rows of Lesser Coverts, and often these three rows never properly develop.
Five short stiff feathers grow from the Thumb, and are known as the Bastard wing. The Assym arc again a series of short stiff feathers, and help to dose the gap between the body of the bird and the innermost feathers of the arm or Secondaries. In birds, such as the Gull tribe, where the Hamm; is very long, these feathers are large and well-developed. They grow in a double series, one from the upper and one from the under surface of the bone.
From the Scaptula, grow a dearly defined group of feathers, which act as a roof, overlapping both the body of the bird and the upper portion of the wing when closed. Consequently, when a bird is at rest and the wing pressed to the body, it is impossible for rain or moisture to trickle down inside the wing.
Plate XXX. WING OF A YOUNG SPARROW (UNDERSIDE) / WING OF A WOOD PIGEON
NOTE—Upon alighting, the first action of a bird is to settle the wings comfortably against the body and beneath this group of feathers. Most small birds require to seek shelter during rain, the Scapularies not being well developed, but in all water birds, also the Eagles and Hawks, their shape and pattern is very marked.
The feathers of the breast, known as the plumage feathers, vary considerably in different types of birds. From this part of the body the down feathers grow, and are found most highly developed in the Heron tribe, where they form large patches over the breast and thighs, known as "Powder down." If carefully examined, this will be found to consist of a number of feather barbs matted together, and of such a friable nature that they disintegrate at the touch into a fine powder.
In some birds, Filo-Plumes play a conspicuous part in the colouration of the plumage. They attain great length and form large patches, as in the white thigh patches of the Cormorant, or give a hoary appearance to the necks of such birds as the Condor Vulture. Little is known of the meaning or use of Filo-Plumes. They are the long hairlike threads which remain over the body of a fowl when plucked.
Many of the Contour feathers are double. That is to say, they have an aftershaft known as Hyporhachis. In the Emu, the aftershaft is the same length as the feather, and it is always well developed in the game birds. The long plume-like feathers growing down the back of these latter, and also the domestic fowl are formed in this manner.
The first aim of the artist or designer when introducing a bird in flight is to introduce a beautiful shape to the wing contour, and so often this is done at the expense of truth, ignoring the fact that every type of bird has its distinctive form of wing. A bird which spends the greater part of its life in the air, such as the Swallow, has a wing in the form of a long, narrow-pointed blade. Whilst in those that fly but short distances, such as the Partridge, the wing takes a broad, rounded shape, and there is an infinite variety between these two extremes. The importance of this cannot be over-estimated by figure painters when introducing angels, cherubs, or evil spirits into their designs. A wing ill-designed and with loose feathers as if in moult is constantly seen in sculptures and designs, when a more decorative result, artistically, would have been gained by a true form of wing. Imagination hesitates at the thought of angels fluttering about with the short quick action of a Sparrow, whilst the spirits of the wind should surely hurl themselves through space with the sinister knife-like wing.
BEAKS, DAGGER TYPES. Kingfisher, Raven (showing feathers on beak), Grebe, Heron, Rook (without feathers on beak)
The typical form is ten Primaries of equal length, but owing to manner of attachment the first feathers appear to be the longer, whilst the remainder appear to diminish. In birds which fly with remarkable rapidity, that is, with rapid strokes of the wing, including the song birds without exception, the second feather is the longest and the first feather abbreviated.
The beak of a bird has a greater scientific than artistic interest ; its many variations being adaptations to different methods of feeding. The earliest known fossil birds were provided with teeth, but modern birds have a sheath composed of horn, and in accordance with the nature of the food, the shape of the sheath or beak varies.
The common form is the Dagger type, serving in addition as a hammer, pair of pincers, or instrument for holding or tearing. Beaks such as this are possessed by the Raven, the Rook, the Kingfisher, and the Finch tribe. More specialised types are found in the Herons and Egrets, with, in addition, an arrangement of the muscles of the Cervicle Vertebra, which enables the head to be darted forward with lightning speed, and so spear or transfix the prey.
BEAKS, PROBES, FISH-EATING TYPES, ETC.
1. FLAMINGO / 2. GANNET / 3. GULL / 4. PENGUIN / 5. DIVER / 6. WOODCOCK / 7. WOODCOCK. / 8. CURLEW / 9. AVOCET / 10. NIGHTJAR / 11 AND 12. FRENCH PARTRIDGE / 13. BRITISH PARTRIDGE / 14. BLACKBIRD SHOWING MOVEMENT OF BEAK IN ACT OF SEIZING A WORM
Birds with this development carry the head with a distinct angular curve to the neck—totally different to the curves taken by the neck of a Swan, Crane, or Flamingo. A Heron in flight carries the head curved back upon the shoulders in complete contrast to a bird similar in build, such as the Stork, where the head is carried outstretched.
Certain forms of beaks have developed to become probes for use in soft mud, examples being the Curlew, the Snipe, the Avocet, and the Woodcock. The beak of the latter has a mobile tip, which is extremely sensitive, and on contact with a worm can grasp and withdraw same from a considerable depth of mud with the minimum amount of effort to the slender beak itself. Very few birds use the feet to convey food to the mouth, but this is done by the Parrots, whose beak is of the pincer type only. In exchange, these birds make as much use of the beak in climbing as of their feet.
The Ducks have a specialised form of beak, suitable to their methods of feeding. The inner edges are provided with rows of small plates, almost like teeth, and their function is to act as strainers, the water being forced out by the movement of the tongue whilst the small animalculae and particles of food are retained.
The fish-eating ducks, like the other fish-eating birds, are provided with a small hook at the end to enable them to hold their slippery prey, and a greater development of this is found in the beaks of the birds of prey, although in the latter its use is more for the purpose of tearing and rending. The feet are in these birds the weapons of offence, being provided with powerful talons, but they are also used to hold down the food whilst tearing it to pieces. Both the Crows and the Vultures hold down their food by means of the feet.
The beak of the grain eaters is usually softer in structure and slightly curved, whilst the Swallows and similar insect eating birds have extremely short beaks with very wide mouths or gape, which enables them to snap and swallow immediately whilst in full flight. The mouth of the Nightjar is fringed with bristles to brush off the wings of the night moths, whilst the succulent body-part is being swallowed.
Plate XXXIII. BEAKS OF BIRDS - BIRDS OF PREY, DUCKS AND FISH-EATING TYPES.
1. GOLDEN EAGLE / 2. DUCK / 3. SHOVELLER DUCK / 4. PENGUIN / 5. CORMORANT / 6. PELICAN
Perhaps no greater scope for decorative treatment exists than in the feet of birds (Plates xxxiv, xxxv, xxxvi), and perhaps no greater failure to make the most of the opportunity is more evident.
The foot of every bird is covered with scales, the pattern of which is a delight in itself, and yet how seldom is this fact made use of for the purpose of design. For the painter of pictures there is some excuse for the neglect, because his problems are those of tone values and colour, and the details have often to be sacrified for the sake of breadth, but the student who wishes to treat the bird in pen and ink or other decorative manner, cannot afford to overlook this pattern.
The principal laws governing the structural formation of the foot are :
The first toe corresponding to the human thumb is placed at the back and consists of one bone only.
The second toe is on the inside of the foot and consists of two bones.
The third or middle toe consists of three bones, and the Fourth or outer toe has four bones. With very few exceptions does this rule vary.
The Passerenes or Perching birds (Plate xxxrv) have the hind toe long, and freely movable to enable them to grasp the bough, and the method of progression upon ground is usually to hop.
The Walking birds (Plate xxxiv), such as Fowls, Game birds, etc., have the hind toe small, often not reaching the ground, and practically without movement, whilst in the Ducks this toe is almost negligible.
Plate XXXIV. FEET. WALKING AND PERCHING TYPES.
1. LAPWING / 2 and 3. PHEASANT / 4 and 5. ROOK / 6. GOLDEN EAGLE / 7. OSPREY / 8 and 9. CHICKEN
Plate XXXV. FEET. EXCEPTIONS TO GENERAL RULE OF 1ST TOE BACKWARD AND 2ND, 3RD, 4TH TOE FORWARD
1. PARROT (ZYGODACTYLE) / 2 AND 3. KINGFISHER (SYNDACTYLE) / 4 AND 5. CUCKOO (ZYGODACTYLE) / 6. GOATSUCKER. SHOWING COMB UPON 3RD TOE / 7. SWIFT. ALL TOES IN FRONT / 8. OWL. TOES IN PAIRS / 9. PTARMIGAN. TOES FEATHERED / 10. BARN OWL. SHOWING REVERSIBLE 4TH TOE AND SERRATED 3RD TOE / 11. GROUSE. TOES FEATHERS.
Plate XXXVI. FEET. TYPES OF WADING BIRDS, SHOWING THE PATTERN FORMED BY THE SCALES
1 MOORHEN / 2. PINTAIL DUCK / 3. PARTRIDGE / 4. MOORHEN / 5. COOT / 6. PINTAIL DUCK / 7. MOORHEN
The Birds of Prey on the contrary have this toe very developed, and capable of considerable movement.
In some birds the three front toes are joined together throughout the greater part of their length, without u any separate movement whatever ; an example being the Kingfisher, who uses the feet for perching and no other purpose, and is known as SyndacOle.
Many of the climbing birds (Plate xxxv), such as the Woodpeckers, have the toes in pairs, two in front and two behind, and the Parrot possesses the power of transferring the second toe either in front or behind at will, hence these feet are known as Zygodactyle.
The Cuckoo is also Zygodactyle.
Most of the Water birds (Plate xxxvr) have the toes joined by a web, but this varies considerably from the foot of a Pelican, wherein all four toes are joined for their entire length, the Duck wherein the three front toes only are joined, the Grebe and the Coot, each toe of which is provided with lobes, and the Moorhen, whose toes are remarkably long and slender, the web being nothing more than a flattening of the under surface of the toe.
The Swallow passes the greater part of its life on the wing, and has no use for legs except for supports when resting. Consequently these have become so small that the bird has a difficulty in rising from the level ground should it by any chance alight thereon. It prefers to launch itself into the air from the eaves, roof-tops, or telegraph wires, and the toes have become of little service except to cling, consequently the four toes are all in front.
Like most other animals whose habitat is ice and snow, the foot of the Ptarmigan is feathered upon the sole, whilst the toes themselves, for the sake of warmth, are covered throughout with feathers.
There is one law, without any exception whatever, governing the arrangement of feathers in the tail of a bird.
Plate XXXVII. TAILS
1. TAIL OF WOOD PIGEON / 2. TAIL OF WOOD PIGEON (CLOSED) / 3. TAIL OF WOOD PIGEON (UNDERSIDE)
4. TAIL OF MAGPIE / 5. TAIL OF ROOK / 6. TAIL OF PARTRIDGE / 7. TAIL OF BLACKCOCK
8. TAIL OF SAND MARTIN / 9. TAIL OF SWALLOW / 10. TAIL OF WILD DUCK
Plate XXXVIII. TAILS
1. PEACOCK, SHOWING REAL AIL BENEATH THE SO-CALLED TAIL / 2. SWALLOW, SHOWING METHOD OF CLINGING TO WALL BY AID OF WINGS / 3. MARTIN, SHOWING METHOD OF CLINGING TO WALL BY AID OF TAIL.
The top feather is always in the centre of the tail, whilst the remainder take their positions beneath one another, thus bringing the outer feathers to the bottom.
NOTE.—Recollection of this fact makes the closed tail of a bird very simple to understand, and will avoid a very common mistake found in drawings of the tail being inserted upside down.
Although the shape of a bird's tail will vary considerably, the number of feathers is usually the same, namely, twelve.
The Wild Duck, however, has sixteen, but the four extra feathers which are in the centre are different in colour and turn upwards, forming the sickle shapes so characteristic of these birds.
The Humming Bird is again an exception, having only seven feathers, whilst the abnormal Fantail Pigeon has developed nearly forty tail feathers.
NOTE.—When drawing birds, particular notice should be taken of the characteristic manner in which some species use their tails to express their emotions. The Blackbird upon alighting, carries the tail high for a few seconds, in a totally different manner to that when hopping along the ground.
PLATE XXXIX. STUDY OF A GUINEA FOWL SHOWING PATTERN ON PLUMAGE
PLATE XL. STUDY OF A PEACOCK SHOWING PATTERN OF THE TAIL
The general rule is that quiet, soft mannered birds hold the tail low and beneath the wing tips, whilst energetic and inquisitive birds, such as the Wren, carry it erect.
At the base of the true tail feathers will be found a series of smaller feathers on both upper and lower sides of the tail, known as the tail coverts, and in certain birds they play an important part in forming sham tails.
The statement that the arrangement of tail feathers has no exception will probably be queried when consideration is given to the tail of the domestic cock. In this bird, however, the real tail consists of short, stiff feathers of dingy hue, arranged to form a roof-shaped wedge, and serves as a support for the beautiful sickle feathers which are actually Upper Tail Coverts.
In all respects, with the exception of the head, the general rule of feather masses applies to the domestic Fowl, and a similar arrangement can be plainly observed when that magnificent bird, the Turkey Cock is in full display. The Pheasant, again, is obedient to the same law, although small variations in some of the details will be observed.
The Peacock is so essentially a bird of decoration and offers such a wide scope for variety of treatment, that this book would be incomplete without a diagram showing the tail outspread (Plate xi.). Whilst in no way desirous to hamper the imaginative treatment or convention of the designer, who, after all, is justified in making his own laws, it is quite possible to treat this bird in a perfectly decorative manner and yet be scientifically correct.
The tail proper of the Peacock consists of twelve grey stiff feathers, hidden by and supporting the decorative tail, which is actually the coverts and feathers of the back. The wings are never visible in front of the tail when the latter is outspread.