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Bird
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"Aves" redirects here. For other uses, see Aves (disambiguation).
For other uses, see Bird (disambiguation).

BirdsFossil range: Late Jurassic–Recent, 150–0 Ma
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Scarlet Robin, Petroica boodang
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Subphylum:
Vertebrata
Class:
AvesLinnaeus, 1758[1]
Subclasses & orders
About two dozen modern orders and several extinct orders and subclasses
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Birds (class Aves) are winged, bipedal, endothermic (warm-blooded), egg-laying, vertebrate animals. There are around 10,000 living species, making them the most varied of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from the 5 cm (2 in) Bee Hummingbird to the 2.75 m (9 ft) Ostrich. The fossil record indicates that birds evolved from theropod dinosaurs during the Jurassic period, around 150–200 Ma (million years ago), and the earliest known bird is the Late Jurassic Archaeopteryx, c 150–145 Ma. Most paleontologists regard birds as the only clade of dinosaurs to have survived the Cretaceous–Tertiary extinction event approximately 65.5 Ma.
Modern birds are characterised by feathers, a beak with no teeth, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a lightweight but strong skeleton. All living species of birds have wings - the now extinct flightless Moa of New Zealand were the only exceptions. Wings are evolved forelimbs, and most can fly, with some exceptions including ratites, penguins, and a number of diverse endemic island species. Birds also have unique digestive and respiratory systems that are highly adapted for flight. Some birds, especially corvids and parrots, are among the most intelligent animal species; a number of bird species have been observed manufacturing and using tools, and many social species exhibit cultural transmission of knowledge across generations.
Many species undertake long distance annual migrations, and many more perform shorter irregular movements. Birds are social; they communicate using visual signals and through calls and songs, and participate in social behaviours including cooperative breeding and hunting, flocking, and mobbing of predators. The vast majority of bird species are socially monogamous, usually for one breeding season at a time, sometimes for years, but rarely for life. Other species have breeding systems that are polygynous ("many females") or, rarely, polyandrous ("many males"). Eggs are usually laid in a nest and incubated by the parents. Most birds have an extended period of parental care after hatching.
Many species are of economic importance, mostly as sources of food acquired through hunting or farming. Some species, particularly songbirds and parrots, are popular as pets. Other uses include the harvesting of guano (droppings) for use as a fertiliser. Birds figure prominently in all aspects of human culture from religion to poetry to popular music. About 120–130 species have become extinct as a result of human activity since the 17th century, and hundreds more before then. Currently about 1,200 species of birds are threatened with extinction by human activities, though efforts are underway to protect them.
Contents[hide]
1 Evolution and taxonomy
1.1 Dinosaurs and the origin of birds
1.2 Alternative theories and controversies
1.3 Early evolution of birds
1.4 Diversification of modern birds
1.5 Modern bird orders: Classification
2 Distribution
3 Anatomy and physiology
3.1 Chromosomes
3.2 Feathers, plumage, and scales
3.3 Flight
4 Behaviour
4.1 Diet and feeding
4.2 Water and drinking
4.3 Migration
4.4 Communication
4.5 Flocking and other associations
4.6 Resting and roosting
4.7 Breeding
4.7.1 Social systems
4.7.2 Territories, nesting and incubation
4.7.3 Parental care and fledging
4.7.4 Brood parasites
5 Ecology
6 Relationship with humans
6.1 Economic importance
6.2 Religion, folklore and culture
6.3 Conservation
7 Notes
8 External links
//
Evolution and taxonomy
Main article: Evolution of birds

Archaeopteryx, the earliest known bird
The first classification of birds was developed by Francis Willughby and John Ray in their 1676 volume Ornithologiae.[2] Carolus Linnaeus modified that work in 1758 to devise the taxonomic classification system currently in use.[3] Birds are categorised as the biological class Aves in Linnaean taxonomy. Phylogenetic taxonomy places Aves in the dinosaur clade Theropoda.[4] Aves and a sister group, the clade Crocodilia, contain the only living representatives of the reptile clade Archosauria. Phylogenetically, Aves is commonly defined as all descendants of the most recent common ancestor of modern birds and Archaeopteryx lithographica.[5]
Archaeopteryx, from the Tithonian stage of the Late Jurassic (some 150–145 million years ago), is the earliest known bird under this definition. Others, including Jacques Gauthier and adherents of the Phylocode system, have defined Aves to include only the modern bird groups, the crown group. This has been done by excluding most groups known only from fossils, and assigning them, instead, to the Avialae[6] in part to avoid the uncertainties about the placement of Archaeopteryx in relation to animals traditionally thought of as theropod dinosaurs.
All modern birds lie within the subclass Neornithes, which has two subdivisions: the Palaeognathae, containing birds that are flightless (like ostriches) or weak fliers, and the wildly diverse Neognathae, containing all other birds.[4] These two subdivisions are often given the rank of