bird, warm-blooded, egg-laying, vertebrate vertebrate, any animal having a backbone or spinal column . Verbrates can be traced back to the Silurian period. In the adults of nearly all forms the backbone consists of a series of vertebrae.
..... Click the link for more information. animal having its body covered with feathers feathers, outgrowths of the skin, constituting the plumage of birds. Feathers grow only along certain definite tracts (pterylae), which vary in different groups of birds.
..... Click the link for more information. and its forelimbs modified into wings wings, flight organs of the bird , the bat , and the insect . Birds' wings are pectoral appendages that are basically the same in skeletal structure as the forelimbs of all higher vertebrates, including the human arm.
..... Click the link for more information. , which are used by most birds for flight. Birds compose the class Aves (see Chordata Chordata (kôrdā`tə,–dä`–)
..... Click the link for more information. ). There are an estimated 9,000 living species.

Birds are believed to be extant members of a group of dinosaurs dinosaur (dī`nəsôr) [Gr., = terrible lizard], extinct land reptile of the Mesozoic era .
..... Click the link for more information. called maniraptors (other maniraptors include Velociraptor and Oviraptor). They share with dinosaurs such characteristics as a foot with three primary toes and one accessory toe held high in back. Early avians include such primitive birds as Arachaeopteryx, the rooster-sized Patagopteryx, and the ichthyornithiforms, skillful flyers with toothed beaks. The fossil remains of the Archaeopteryx Archaeopteryx (är'kēŏp`tərĭks) [Gr.
..... Click the link for more information. , which date to the Jurassic period, show reptilian tails, jaws with teeth, and clawed wings, but feathers were well developed. Pterosaurs pterosaur (tĕr`əsôr') [Gr., = winged lizard], extinct flying reptile (commonly called pterodactyl [Gr.
..... Click the link for more information. , another group of flying reptiles, did not share the common characteristics of birds and dinosaurs and are not considered birds. Whether the capacity for flight arose in tree-living dinosaurs that glided from branch to branch (the "trees-down" hypothesis) or in fast-running terrestrial dinosaurs (the "ground-up" hypothesis) continues to be debated. Indeed, the inclusion of birds in the dinosaur family tree, although accepted by most paleontologists, is debated by some, and the identification (2000) of the oldest known feathers on 220-million-year-old, four-legged reptile fossil, Longisquama insignis, raised questions concerning the theory.

Birds are of enormous value to humanity because of their destruction of insect pests and weed seeds. Many are useful as scavengers. The game birds hunted for food and sport include grouse grouse, common name for a game bird of the colder parts of the Northern Hemisphere. There are about 18 species. Grouse are henlike terrestrial birds, protectively plumaged in shades of red, brown, and gray.
..... Click the link for more information. , pheasant pheasant, common name for some members of a family (Phasianidae) of henlike birds related to the grouse and including the Old World partridge, the peacock, various domestic and jungle fowls, and the true pheasants (genus Phasianus).
..... Click the link for more information. , quail quail, common name for a variety of small game birds related to the partridge, pheasant, and more distantly to the grouse. There are three subfamilies in the quail family: the New World quails; the Old World quails and partridges; and the true pheasants and seafowls.
..... Click the link for more information. , duck duck, common name for wild and domestic waterfowl of the family Anatidae, which also includes geese and swans. It is hunted and bred for its meat, eggs, and feathers. Strictly speaking, duck refers to the female and drake to the male.
..... Click the link for more information. , and plover plover (plŭv`ər), common name for some members of the large family Charadriidae, shore birds, small to medium in size, found in
..... Click the link for more information. . The chief domestic birds are the chicken (see poultry poultry, domesticated fowl kept primarily for meat and eggs; including birds of the order Galliformes, e.g., the chicken, turkey , guinea fowl , pheasant , quail , and peacock ; and natatorial (swimming) birds, e.g., the duck and goose .
..... Click the link for more information. ), duck, goose goose, common name for large wild and domesticated swimming birds related to the duck and the swan. Strictly speaking, the term goose is applied to the female and gander to the male.
..... Click the link for more information. , turkey turkey, common name for a large game and poultry bird related to the grouse and the pheasant. Its name derives from its "turk-turk" call. Turkeys are indigenous to the New World; American fossils date back 40 million years to the Oligocene.
..... Click the link for more information. , and guinea fowl guinea fowl (gĭn`ē), common name for any of the seven species of gallinaceous birds of the family Numididae, native to Africa and
..... Click the link for more information. . Parrots parrot, common name for members of the order Psittaciformes, comprising 315 species of colorful birds, pantropical in distribution, including the parakeet . Parrots have large heads and short necks, strong feet with two toes in front and two in back (facilitating
..... Click the link for more information. and many members of the finch finch, common name for members of the Fringillidae, the largest family of birds (including over half the known species), found in most parts of the world except Australia.
..... Click the link for more information. family are kept as pets.

Characteristic Features and Behaviors

Like mammals, they have a four-chambered heart, and there is a complete separation of oxygenated and deoxygenated blood. The body temperature is from 2° to 14° higher than that of mammals. Birds have a relatively large brain, keen sight, and acute hearing, but little sense of smell. Birds are highly adapted for flight flight, sustained, self-powered motion through the air, as accomplished by an animal, aircraft, or rocket.

Animal Flight

Adaptation for flight is highly developed in birds and insects .
..... Click the link for more information. . Their structure combines lightness and strength. Body weight is reduced by the presence of a horny bill instead of heavy jaws and teeth and by the air sacs in the hollow bones as well as in other parts of the body. Compactness and firmness are achieved by the fusion of bones in the pelvic region and in other parts of the skeleton. The heavier parts of the body—the gizzard, intestines, flight muscles, and thigh muscles—are all strategically located for maintaining balance in flight. Feathers, despite their lightness, are highly protective against cold and wet. The flight feathers, especially, have great strength. Feathers are renewed in the process of molting molting, periodical shedding and renewal of the outer skin, exoskeleton, fur, or feathers of an animal. In most animals the process is triggered by secretions of the thyroid and pituitary glands.
..... Click the link for more information. . Some birds, such as the ostrich, the penguin, and the kiwi, lack the power of flight and have a flat sternum, or breastbone, without the prominent keel to which the well-developed flight muscles of other birds are attached. The bills of birds are well adapted to their food habits. Specialized bills are found in the crossbill, hummingbird, spoonbill, pelican, and woodpecker.

In the majority of species there are differences between male and female in plumage coloring. In these birds the male (except in the phalarope) is usually the more brilliant or the more distinctly marked and is the aggressor in courtship. Unusual courtship displays are performed by several species, particularly by the ruffed grouse, the bird of paradise, the crane, the pheasant, and the peacock. Birdsong birdsong. Song, call notes, and certain mechanical sounds constitute the language of birds. Song is produced in the syrinx, whose firm walls are derived from the rings of the trachea, and is modified by the larynx and tongue.
..... Click the link for more information. reaches its highest development during the breeding season, and singing ability is usually either restricted to or superior in the male. Most birds build a nest nest, structure for the reception and incubation of the eggs of birds, reptiles, insects, and some fish or for the parturition of mammals, and also for the care of the young during their period of helplessness.
..... Click the link for more information. in which to lay their eggs. Some birds, such as the oriole, weave an intricate structure, while others lay their eggs directly on the ground or among a few seemingly carelessly assembled twigs. Eggs vary in size, number, color, and shape. In spring and fall many birds migrate. Not all of the factors motivating this behavior are fully understood. These trips often involve flights of hundreds and even thousands of miles over mountains and oceans (see also migration of animals migration of animals, movements of animals in large numbers from one place to another. In modern usage the term is usually restricted to regular, periodic movements of populations away from and back to their place of origin.
..... Click the link for more information. ).

Bibliography

Among the periodicals devoted to the study of bird life are the Auk, the Condor, and the Wilson Bulletin. Books on birds include the many guides by R. T. Peterson Peterson, Roger Tory, 1908–96, American ornithologist, writer, and illustrator, b. Jamestown, N.Y. He became famous with his best-selling pocket-sized Field Guide to the Birds
..... Click the link for more information. ; the life histories of North American birds in F. Gill and A. Poole, ed., The Birds of North America (1992–2003); R. M. De Schauensee, A Guide to the Birds of South America (1970); A. Rutgers and K. A. Norris, ed., Encyclopaedia of Aviculture (Vol. I, 1971, and Vol. II, 1972); U.S. Bureau of Sports Fisheries and Wildlife, Birds in Our Lives (1970); J. Van Tyne and A. J. Berger, Fundamentals of Ornithology (1971); S. Cramp, ed., Handbook of the Birds of Europe, the Middle East, and North Africa (5 vol., 1977–88); M. Walters, Birds of the World (1980); B. King et al., The Collins Field Guide to the Birds of South-East Asia (1988); J. Farrand, Jr., Eastern Birds (1988) and Western Birds (1988); S. Chatterjee, The Rise of Birds (1997); P. Shipman, Taking Wing (1998); D. Attenborough, The Life of Birds (1998); D. A. Sibley, The Sibley Guide to Birds (2000).

bird

Principal features of a songbird.

Any of the warm-blooded, beaked vertebrates of the class Aves, including more than 9,600 living species. A covering of feathers distinguishes birds from all other animals. Birds have a four-chambered heart (like mammals), forelimbs modified into wings, and keen vision, and their eggs have calcium-rich eggshells. Their sense of smell is not highly developed. Birds are found almost worldwide in diverse habitats on both land and water. Dietary preferences and nest structure vary widely. Almost all species incubate their eggs. Flying birds have evolved skeletons in which part of the bone is replaced by air spaces, an adaptation for reducing weight. The crop, an enlarged part of the esophagus used for temporary food storage, enables birds to feed while in flight. Humans use wild and domesticated birds and their eggs for food, hunt wild birds for sport, and use feathers for decoration and insulation. More than 1,000 extinct species of bird have been identified from fossil remains; the earliest fossil bird known is Archaeopteryx.