Do you know? The structure of the bird? During their period of evolution, lasting several hundreds of
thousands of years, birds became masters of the air. One of the main reasons was probably the fact that terrestrial animals posed no threat to their food supply. But with the passage of time, some species reverted to life on the ground or in water, often losing entirely the ability to fly and becoming runners or swimmers.

Bird topography:

Structure of the bird

1) forehead 2) crown 3) hind neck 4) nape 5) shoulder 6) back 7) upper tail coverts 8) tail feathers 9) under tail coverts 10) belly 11) breast 12) neck 13) throat 14) chin 15) cheek 16) ear region 17) thigh 18) tarsus 19) hind toe 20) inner toe 21) rniddle toe 22) outer toe 23) bill ridge 24) upper mandible 25) lower rnandible 26) nostril 27) cere 28) wing coverts 29) secondaries 30) prixnaries.

How are birds fly?

For most birds, however, a flight is the typical characteristic, and their degree of flight capability, as well as their flight silhouette, are important recognition factors, enabling even the layman to identify them at first glance as members of a specific group. The form of flight often differs greatly between species of birds and is allied to the general shape of their wings and wing surface. Birds capable of rapid and sustained flight have long, narrow, crescent-shaped wings (the swift and hobby), together with a slender body that offers minimum resistance to the air.

The swift has evolved into such an efficient flying machine that it has poorly developed legs and is fairly helpless if grounded. They normally alight on ledges or posts and take off by dropping forward into the air. In complete contrast are the ground birds, such as those of the order Gallinae, of which pheasants are an example. They have fairly short, broad wings and plump bodies and, apart from a few exceptions, gallinaceous birds are indifferent fliers.

They are able to take to the air quickly but can fly for only a very short distance. Consequently, they are usually resident birds and do not migrate. This does not mean that all large land birds cannot perform well in the air: some birds of prey, such as the buzzard and kestrel, can remain hovering in the air over a single spot for some time. Each species of bird has also a typical flight silhouette, that is the shape or outline of the body, tail and wings when on the wing. Some, like the stork, swan and many more, fly with neck outstretched; others, such as the heron, carry it bent into an S.

Surface of a bird’s body

The surface of a bird ‘s body is covered with feathers, arranged in most species in definite tracts called pteryla. Only in some rare cases, such as the penguins, are the feathers distributed evenly over the entire body surface. The bare spaces between the feathered tracts are called apteria, but these are masked by the surrounding feathers. Those which give the body its typical shape are the outer flight and contour feathers, providing also some insulation. Beneath them is a layer of soft down which gives added insulation.

Other types include filament or filoplume feathers, a degenerate feather with no known function, and bristle feathers. The latter are peculiar to a few birds such as the nightjar, the bristles around their mouth (gape) helping to catch insects during flight. The strongest are the flight feathers, which are firm but flexible and serve to keep the bird airborne. Those at the tail serve to steer the bird on its course and maintain balanced flight. In some cases, such as the woodpecker, they serve also as a prop in climbing the trunks of trees or chipping out a hollow.

Feathers of a bird

Most birds feathers are shed and replaced regularly, this process is known as moulting. Old, worn feathers fall out
as the new ones grow, and the wing quills and tail feathers are shed successively so that the bird does not lose its power of flight. Only in some species, ducks, for example, are they shed all at one time, the birds thus going through a flightless period during which they remain concealed amidst reeds and rushes until new feathers grow in. But not all birds are subjects to complete moulting. Herons, bitterns and hawks have what are known as powder-down feathers which grow continuously, the tips of which disintegrate into a water-resistant powder used in preening.

Coloration of birds

Some birds don two differently coloured plumages in a year: the brightly coloured breeding plumage, especially in males, and the more sober non-breeding or winter plumage, usually more or less similar for both sexes. This change of coloration is characteristic, of ducks, some shorebirds, finch-types and other birds.

In some species, the male and female have the same coloration, the chiffchaff, treecreeper and tit being typical examples, while in others the colour of the male and sometimes the shape of various feathers are markedly different. Typical are the pheasant and capercaillie, this being known as sexual dimorphism.

Some birds have so-called protective colouring that helps to conceal them from enemies. Thus, for example, the female pheasant, capercaillie and black grouse are sombrely coloured to escape the notice of predators, especially during the nesting period when the sitting hen is easy prey. Owls, too, have protective colouring, both males and females, for they have many enemies, especially in daylight.

Birds of prey and corvines pursue owls if they see them during the day, and that is why owls are so drably coloured, often resembling the stump of a dead branch as they perch among the treetops.

Feet of a bird

Bird’s feet have varied shapes, depending on the way of life of a given species. Treecreepers have toes with long, sharp claws that grip the bark as the bird climbs. Woodpeckers, too, have long, sharp claws that cut deep into the tree bark serving as an additional means of support to that provided by their strong tail feathers. The toes of woodpeckers are further adapted for climbing, two pointing forward and two backward. The feet of the nightjar are short with weak toes, making it almost impossible for the bird to move on the ground.

It is also incapable of grasping a branch in the usual manner, which explains why it perches lengthwise and not crosswise. Birds of prey have huge claws on all four toes; those of eagles and hawks are extremely long, curved and sharp, whereas those of the vultures are straight and blunt, for these species have legs adapted to move on the ground where they seek their food — carrion. Specially adapted are the toes of owls, with their long, sharply curved claws, the peculiarity, in this case, being that the outer toe may be directed forward, outward or completely backward, thus enabling the owl to catch its prey between opposite facing claws — a weapon few victims escape.

One other predator, the osprey, has a reversible outer toe to facilitate catching fish under water, plus small spines on the pad of each toe to help in holding its slippery prey. Large, strong feet with blunt but strong claws are characteristic of the gallinaceous birds and serve to dig up seeds, insects and worms from the ground. And, of course, one must not overlook webbed toes of the many birds that live and hunt primarily on and under water.

Shape of a bird’s beak

The shape of a bird’s beak is also adapted for the function it serves, namely obtaining food. Thus, the bills of warblers are slender and slightly downcurved at the tip, so that they can easily catch small insects and their larvae. Flycatchers have a broad, flat and relatively wide bill, making it easier to catch insects in the air. The bill of thrushes resembles that of warblers but is stronger, for they eat larger insects, worms and also berries.

Tits have a strong bill to break hard seed covering; tree creepers a long, downcurved bill that is very slender at the tip to help them extricate small insects, their eggs and larvae from cracks in the bark of trees. The bill of finch-type birds is stout and cone-shaped, useful in hulling seeds; that of the hawfinch, for instance, is unusually stout and enables it to crack even the hardest shells to get at the tender seeds and kernels inside. Crossbills, as their name indicates, have bills with overlapping tips to facilitate the extraction of seeds from the cones of conifers. Corvine birds, which are omnivorous, have an extremely large and stout bill.

The nightjar, on the other hand, has a short but very wide bill with stiff bristles at the gape, which help it to catch insects on the wing. The bills of owls are downcurved and stout, testifying to their predatory way of life, the same as those of raptors, where the upper bills are not only downcurved but also have sharp edges that enable the birds to rip and tear the flesh of animals and to ‘cut off’ softer pieces. Some raptors, such as members of the family Falconidae, also have one or hornier ‘teeth’ in the upper bill, which further facilitates the tearing of flesh.

Those of gallinaceous, or fowl-like, birds are comparatively short but very stout. In some species, they are even shovel-shaped to facilitate turning of the earth in which the birds seek their food. Pigeons, too, have short bills with swollen ceres at the base, but with fairly hard tips which enable the pigeon to gather a variety of seeds and fruits. Woodpeckers have bills specially adapted for chiselling wood and uncovering concealed grubs.

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