Birds are a group of warm-blooded vertebrates constituting the class Aves (/ˈeɪviːz/), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight skeleton. Birds live worldwide and range in size from the 5.5 cm (2.2 in) bee hummingbird to the 2.8 m (9 ft 2 in) common ostrich. There are over 11,000 living species, more than half of which are passerine, or "perching" birds. Birds have wings whose development varies according to species; the only known groups without wings are the extinct moa and elephant birds. Wings, which are modified forelimbs, gave birds the ability to fly, although further evolution has led to the loss of flight in some birds, including ratites, penguins, and diverse endemic island species. The digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some waterbirds, have further evolved for swimming. The study of birds is called ornithology.
Birds are feathered theropod dinosaurs and constitute the only known living dinosaurs. Likewise, birds are considered reptiles in the modern cladistic sense of the term, and their closest living relatives are the crocodilians. Birds are descendants of the primitive avialans (whose members include Archaeopteryx) which first appeared during the Late Jurassic. According to recent estimates, modern birds (Neornithes) evolved in the Late Cretaceous and diversified dramatically around the time of the Cretaceous–Paleogene extinction event 66 million years ago, which killed off the pterosaurs and all non-avian dinosaurs.
Many social species preserve knowledge across generations (culture). Birds are social, communicating with visual signals, calls, and songs, and participating in such behaviours as cooperative breeding and hunting, flocking, and mobbing of predators. The vast majority of bird species are socially (but not necessarily sexually) monogamous, usually for one breeding season at a time, sometimes for years, and rarely for life. Other species have breeding systems that are polygynous (one male with many females) or, rarely, polyandrous (one female with many males). Birds produce offspring by laying eggs which are fertilised through sexual reproduction. They are usually laid in a nest and incubated by the parents. Most birds have an extended period of parental care after hatching.
Many species of birds are economically important as food for human consumption and raw material in manufacturing, with domesticated and undomesticated birds being important sources of eggs, meat, and feathers. Songbirds, parrots, and other species are popular as pets. Guano (bird excrement) is harvested for use as a fertiliser. Birds figure throughout human culture. About 120 to 130 species have become extinct due to human activity since the 17th century, and hundreds more before then. Human activity threatens about 1,200 bird species with extinction, though efforts are underway to protect them. Recreational birdwatching is an important part of the ecotourism industry. (Full article...)
A bird hybrid is a bird that has two different species as parents. The resulting bird can present with any combination of characteristics from the parent species, from totally identical to completely different. Usually, the bird hybrid shows intermediate characteristics between the two species. A "successful" hybrid is one demonstrated to produce fertile offspring. According to the most recent estimates, about 16% of all wild bird species have been known to hybridize with one another; this number increases to 22% when captive hybrids are taken into account. Several bird species hybridize with multiple other species. For example, the mallard (Anas platyrhynchos) is known to interbreed with at least 40 different species. The ecological and evolutionary consequences of multispecies hybridization remain to be determined.
In the wild, some of the most frequently reported hybrids are waterfowl, gulls, hummingbirds, and birds-of-paradise. Mallards, whether of wild or domestic origin, hybridize with other ducks so often that multiple duck species are at risk of extinction because of it. In gulls, Western × Glaucous-winged Gulls (known as "Olympic Gulls") are particularly common; these hybrids are fertile and may be more evolutionarily fit than either parent species. At least twenty different hummingbird hybrid combinations have been reported, and intergeneric hybrids are not uncommon within the family. (Full article...)Glareolidae is a family of birds in the wader suborder Lari. It contains two distinct groups, the pratincoles and the coursers. The atypical Egyptian plover (Pluvianus aegyptius), traditionally placed in this family, is now known to be only distantly related (basal of clade Charadrii).
The family contains 17 species in 4 genera. (Full article...)Anatomy: Anatomy • Skeleton • Flight • Eggs • Feathers • Plumage
Evolution and extinction: Evolution • Archaeopteryx • Hybridisation • Late Quaternary prehistoric birds • Fossils • Taxonomy • Extinction
Behaviour: Singing • Intelligence • Migration • Reproduction • Nesting • Incubation • Brood parasites
Bird orders: Struthioniformes • Tinamiformes • Anseriformes • Accipitriformes • Galliformes • Gaviiformes • Podicipediformes • Procellariiformes • Sphenisciformes • Pelecaniformes • Ciconiiformes • Phoenicopteriformes • Falconiformes • Gruiformes • Charadriiformes • Pteroclidiformes • Columbiformes • Psittaciformes • Cuculiformes • Strigiformes • Caprimulgiformes • Apodiformes • Coraciiformes • Piciformes • Trogoniformes • Coliiformes • Passeriformes
Bird lists: Families and orders • Lists by region
Birds and humans: Ringing • Ornithology • Bird collections • Birdwatching • Birdfeeding • Conservation • Aviculture
Free online resources:
There is also Birds of North America, Cornell University's massive project collecting information on every breeding bird in the ABA area. It is available for US$40 a year.
For more sources, including printed sources, see WikiProject Birds.
The species was on the brink of extirpation in the contiguous United States (while flourishing in much of Alaska and Canada) late in the 20th century, but now has a stable population and has been officially removed from the U.S. federal government's list of endangered species. The bald eagle was officially reclassified from "endangered" to "threatened" on July 12, 1995 by the U.S. Fish & Wildlife Service. On July 6, 1999, a proposal was initiated "To Remove the Bald Eagle in the Lower 48 States From the List of Endangered and Threatened Wildlife."
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More outstanding tasks at the project's cleanup listing, Category:Birds articles needing attention, and Wikipedia:WikiProject Birds/Todo.
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