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External Features of Birds

© Mazhar Ali

Of all the vertebrates, Aves (its a class which includes all kinds of Birds) is a group consisting of members which are more like one another, and this is the group representing true life in the sense one defines it. Small differences that are found in the birds are usually adaptive, enabling each kind to perform its necessary activities more efficiently. The body is divided into a small head, long and mobile neck, fusiform trunk and small tail provided with long feathers. The skin is thin, loose and dry, there being no sweat glands. The only glands present are the Cutaneous Glands at base of the tail. The skin is covered with feathers, and the scales on the legs and feet; and bills and claws are specialized scale like structure. The color pattern of the feathers is more variable than those of any other Vertebrates. There may be protective coloration rendering the Bird less visible, i.e., for concealment, or it may be a means of recognition and sexual stimulation. Some Birds are of one color, which is almost uniform, as Black Crows and White Egrets, but feathers of most species are marked with spots, stripes and bars. Birds of Arid region are pale-colored while those of humid places are darker. In iridescent feathers interference of light in thin surface films give color like those of soap bubbles.

In blue color incident light is reflected from a turbid porous layers overlying a deposit of melanin pigment which is very common, and laid down in feathers by special cells in the papillae. In some species both sexes acquire a nuptial plumage by a pre-nuptial molt in summer. In most species males are often brilliantly colored than the females.

The beak or bill is characteristically modified in Birds according to their food habits. Although some species are strictly confined to one diet, some are able to adapt themselves to the variable food that is available. Carnivorous Birds (flesh eaters) are of two kinds: those, which eat flesh of Birds or Mammals, and those, which eat fish. In the former case, such as Eagles, Hawks, Kites, Owls, the beak is stout, short and sharp. It is often curved and terminate in terminate in a hook-like structure. In the latter case, such as Gulls, Song thrush, Cormorants and others, the bill, is moderately longer and very slightly curved. In Birds feeding in marshy places, such has curlew the beak is quite long and thin, and is meant for selecting food from mud in a different way. The food consists of mostly worms and other soft bodied invertebrates (creatures without backbone). In most insectivorous birds as swallows and flycatchers, which captures living insects in flight, the beak is rather small and slender, but capable to a wide opening. In Woodpecker, however, it is much longer and stronger with other modifications, such as the long and sticky tongue so that beak can probe insects from the bark of trees and lick them with the help of the tongue. In the case of Ducks and other birds the beak is flattened and depressed, with margin provided with many transverse horny ridges. In the seeds-eating birds, such as Finches, House sparrows and other, the bill is short, thick and strong. In Hornbill, the beak is large because the bird has to push through dense foliage to obtain the fruit, which may have a hard coat. In Parrots, the beak is short and stout, with the terminal part transversely ridged on its under surface, and is able to move on the skull and able to crush fruit with the help of jaw muscles. In the lesser Flamingo it is large, curved and flattened. This bird feeds on Blue-green algae and Phytoplankton, collected by a fitter system of the jaws, using a current of water produced by the a filter system of the jaws, using a current of water produced by the sucking mouth and piston like tongue. A high degree of specialization is reached in the Humming-birds that eat nectar of flowers. The beak may be long or short according to the type of flower visited and the tongue is provided with a tubular tip. The Pelican, which chiefly feeds on fish, has a pouch, formed by the lower portion of the beak, in which it can store number of fish. The food so stored may be eaten at leisure or carried to the developing young.

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