Bird Wallpapers

Bird Animals - photo wallpapers; Megawallpapers.org: For other meanings of bird, see bird (disambiguation). Birds: Lemon-bellied Flycatcher; Scientific classification; Kingdom: Animalia; Phylum: Chordata; Class: Aves. Orders: Many - see section below. Birds are bipedal, warm-blooded, egg-laying vertebrates characterized primarily by feathers, forelimbs modified as wings, and hollow bones. Birds range in size from the tiny hummingbirds to the huge Ostrich and Emu. Depending on taxonomic viewpoint, there are between about 8,800-9,800 living and about 120-130 extinct bird species in the world, making them the most diverse class of terrestrial vertebrates. Birds are a very differentiated class, with some feeding on nectar, seeds, insects, rodents, fish, carrion, or other birds. Most birds are diurnal, or active during the day. Some birds, such as the owls and nightjars, are nocturnal or crepuscular (active during twilight hours). Many birds migrate long distances to utilise optimum habitats (e.g., Arctic Tern) while others spend almost all their time at sea (e.g. the Wandering Albatross). Common characteristics of birds include a bony beak with no teeth, the laying of hard-shelled eggs, high metabolic rate, and a light but strong skeleton. Most birds are characterised by flight, though the ratites are flightless, and several other species, particularly on islands, have also lost this ability. Flightless birds include the penguins, Ostrich, kiwi, and the extinct Dodo. Flightless species are vulnerable to extinction when humans or the mammals they introduce arrive in their habitat, for example the Great Auk, flightless rails, and the moa of New Zealand. Evolution: Birds are generally considered to have evolved from theropod dinosaurs. Specifically, birds are members of Maniraptora, a group of theropods which includes dromaeosaurs and oviraptorids. The exact boundary between dinosaurs and birds is unclear, especially with the recent discoveries in North-east China (Liaoning Province) demonstrating that many small theropod dinosaurs had feathers. The recently discovered dromaeosaur, Cryptovolans, was capable of powered flight, contained a keel and had ribs with an uncinate process. In fact, Cryptovolans makes a better "bird" than Archaeopteryx who is missing some of these modern bird features. Because of this, some paleontologists have suggested that dromaeosaurs are actually basal birds whose larger members are secondarily flightless. Evidence for this theory is currently inconclusive. It should be noted that although ornithischian (bird-hipped) dinosaurs share the same hip structure as birds, birds actually originated from the saurischian (lizard-hipped) dinosaurs, and thus arrived at their hip structure condition independently. In fact, the bird-like hip structure developed a third time among a peculiar group of theropods, the Therizinosauridae. The early bird Archaeopteryx, from the Jurassic, is well-known as one of the first "missing links" to be found in support of evolution in the late 19th century. It remains the most primitive known bird. Other early birds now extinct include the Confuciusornithidae, Enantiornithes, Ichthyornis, and Hesperornithiformes, a group of flightless divers resembling grebes. Modern birds are classified in Neornithes. The flightless Palaeognaths, the Ostrich group, were first to diverge from the avian lineage, and it is now thought that the basal divergence from the remaining Neognathes was that of the Galloanseri, the superorder containing the Anseriformes (ducks, geese and swans), and the Galliformes (the pheasants, grouse and their allies). See the chart. Sibley & Ahlquist's Phylogeny and Classification of Birds (1990) is a landmark work on the classification of birds (although frequently debated and constantly revised). Bird orders: This is a list of the taxonomic orders in the class Aves. List of birds gives a more detailed summary, including families. Struthioniformes, Ostrich, emus, kiwis, and allies; Tinamiformes, tinamous; Anseriformes, waterfowl; Galliformes, fowl; Sphenisciformes, penguins; Gaviiformes, loons; Podicipediformes, grebes; Procellariiformes, albatrosses, petrels, and allies; Pelecaniformes, pelicans and allies; Ciconiiformes, storks and allies; Phoenicopteriformes, flamingos; Accipitriformes, eagles, hawks and allies; Falconiformes, falcons; Turniciformes, button-quail; Gruiformes, cranes and allies Charadriiformes, plovers and allies; Pteroclidiformes, sandgrouse; Columbiformes, doves and pigeons; Psittaciformes, parrots and allies; Cuculiformes, cuckoos; Strigiformes, owls; Caprimulgiformes, nightjars and allies; Apodiformes, swifts [br]Coraciiformes, kingfishers; Piciformes, woodpeckers and allies; Trogoniformes, trogons; Coliiformes, mousebirds [br]Passeriformes, passerines. Reproduction: Although most male birds have no external sex organs, the male does have two testes which become hundreds of times larger during the breeding season to produce sperm. The female's ovaries also become larger, although only the left ovary actually functions.In the males of species without a phallus (see below), sperm is stored within the proctodeum compartment within the cloaca prior to copulation. During copulation, the female moves her tail to the side and the male either mounts the female from behind or moves very close to her. He moves the opening of his cloaca, or vent, close to hers, so that the sperm can enter the female's cloaca, in what is referred to as a cloacal kiss. This can happen very fast, sometimes in less than one second. The sperm is stored in the female's cloaca for anywhere from a week to a year, depending on the species of bird. Then, one by one, eggs will descend from the female's ovaries and become fertilized by the male's sperm, before being subsequently laid by the female. The eggs will then continue their development in the nest. Many waterfowl and some other birds, such as the ostrich and turkey, do possess a phallus. Except during copulation, it is hidden within the proctodeum compartment within the cloaca, just inside the vent. The avian phallus differs from the mammalian penis in several ways, most importantly in that it is purely a copulatory organ and is not used for dispelling urine. A juvenile Laughing Gull on the beach at Atlantic City.After the eggs hatch, parent birds provide varying degrees of care in terms of food and protection. Precocial birds can care for themselves independently within minutes of hatching; altricial hatchlings are helpless, blind, and naked, and require extended parental care. The chicks of many ground-nesting birds such as partridges and waders are often able to run virtually immediately after hatching; such birds are referred to as nidifugous. The young of hole-nesters, on the other hand, are often totally incapable of unassisted survival. "Fledging" is the process of a chick acquiring feathers until it can fly. Some birds, such as pigeons, geese, and Red-crowned Cranes, remain with their mates for life (or for a long period) and may produce offspring on a regular basis. [br]From Wikipedia, the free encyclopedia.

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