Birds evolved from reptilian ancestors within the Jurassic period, two hundred million years ago. At the identical time, mammals were evolving from a completely different line of reptilians.
The foremost characteristic feature of birds is the possession of feathers. As a result of the bird-like reptiles of the Jurassic were changing into warm-blooded, the principle advantage of the feathery covering was most likely the reduction of warmth loss from a warm body. Fashionable birds have temperatures of concerning forty-41 degrees C which contributes to the high rate of metabolism necessary for the muscular activity involved in flight.
The higher and lower mandibles of a bird are extended to make a beak. The form of the beak varies with the species. There are long, narrow beaks which penetrate into flowers for their nectar; short stout beaks which crack open seeds; sharp, hooked beaks which tear flesh from prey.
There are two layers of feathers covering the body. The down feathers are fluffy and type an insulating layer shut to the body. The contour feathers are flatter and broader and make a water-proof layer also giving the bird its characteristic shape The ability of flight became potential because the skeleton of the fore-limbs became modified to form wings and therefore the flight feathers developed. The flight feathers on the wings have long shafts and flat vanes on every facet of the shaft. The vanes are formed from parallel rows of fine filaments which interlock in such way that, should the feathers be damaged, they'll simply be restored by preening with the beak.
The feathers are produced from pits within the skin, abundant as hairs are produced in mammals. Muscles within the skin can move the feathers, fluffing them out in cold weather for example. The skin is loose and dry with few glands except for an oil-secreting gland which carries the tail feathers. The birds spread the oil from this gland over their feathers once they preen, so increasing the water repellent properties.
Flight is of three kinds, soaring, gliding and flapping. For gliding and soaring the bird extends its wings, keeping them still apart from small adjustments. In soaring, the bird is carried upwards on currents of heat air (thermals) rising from the ground. In gliding the bird slowly loses height while gaining forward momentum. These sorts of flying could be combined, e.g. when sea-birds use the currents of wind blowing up a cliff face.
In flapping flight, powerful muscles depress and lift the wing rhythmically, forcing air down and backwards which gives the bird lift and forward movement. During the up-stroke the wings are flexed at the wrist and supply less air resistance than within the down-stroke where they're totally extended. The method the flight feathers overlap also helps; air pressure forces the vanes apart on the upstroke however closes them on the down-stroke.
Other than the wings, alternative features facilitate to form flight possible. The contour feathers give the bird a streamlined form; the bones are hollow and so terribly light; parts of the skeleton are fused along making a rigid 'box' which resists the tendency to be squashed when the flight muscles contract; the flight muscles are terribly powerful and are attached to a keel-like extension of the breastbone; the bird's raised temperature enhances the high metabolic rate that is needed to provide the energy for flapping flight.
All birds reproduce by eggs that are fertilised before laying. The male bird, when a successful courtship show, mounts the feminine, applies his cloaca to hers and passes sperms into her reproductive tract. As the eggs travel down the oviduct, a layer of albumen is added and eventually a onerous shell. The eggs are laid in a very nest which might be carefully constructed from vegetation or be simply a scrape in the ground or a ledge on a cliff. The eggs are kept heat by incubation. That's, the bird covers them with her body where they are kept close to the skin. The young finally hatch out by pecking their way out of the shell.
The chicks of ground-nesting birds, including waterfowl, hatch out with a downy covering of feathers and can run regarding or swim during a terribly short time. They keep close to the parent bird who, within the case of waterfowl, may feed them or they will merely forage for food, learning what's suitable or unsuitable to eat.
The chicks that hatch in nests above ground are often while not feathers and are kept heat by the adult brooding them, that's, covering them with the body, which conjointly keeps off the rain. Each adults bring food to the nest and feed the chicks till they are old enough to depart the nest, and continue to feed them for it slow afterwards.
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Dorish Hill Grant has been writing articles online for nearly 2 years now. Not only does this author specialize in Biology, you can also check out his latest website about:
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