Bird

Birds
A composite image shawin the diversity o birds; 18 biological orders are depictit in this image (frae tap, left tae richt): Cuculiformes, Ciconiiformes, Phaethontiformes, Accipitriformes, Gruiformes, Galliformes, Anseriformes, Trochiliformes, Charadriiformes, Casuariiformes, Psittaciformes, Phoenicopteriformes, Sphenisciformes, Pelecaniformes, Suliformes, Coraciiformes, Strigiformes, Piciformes.
Scientific classification
Kinrick:	Animalia
Phylum:	Chordata
Clade:	Sauropsida
Clade:	Avemetatarsalia
Clade:	Ornithurae Gauthier, 1986
Cless:	Aves Linnaeus, 1758
Subclasses
†Archaeornithes * †Enantiornithes †Hesperornithes †Ichthyornithes Neornithes An see text

Birds (Aves) are a group o endothermic vertebrates, characterised bi feathers, tuithless beakit jaws, the layin o haurd-shelled eggs, a heich metabolic rate, a fower-chaumbered hert, and a lichtweicht bit pure tough skelet. Birds bide warldwide and range in size fae the 5 cm (2 in) bee hummingbird tae the 2.75 m (9 ft) ostrich. Thay rank as the cless o tetrapods wi the maist livin species, at aboot ten thoosand, wi mair nor hauf o thae bein passerines, whiles kent as perching birds or, less richtly, as songbirds.

The fossil record indicates that birds are the lest surviving dinosaurs, termed avian dinosaurs, haed evolved frae feathered ancestors inwith the theropod group o saurischian dinosaurs. True birds erest appeared while the Cretaceous feck, aroond 100 million years aby. DNA-evident shaws that birds diversified dramatically aroond the time o the cretaceous–paleogene extinction event that kilt aff a ither dinosaurs. Birds in Sooth America owercome this event and syne migrated tae ither bits o the warld via multiple laund brigs, while diversifying while periods o global cooling. primitive bird-lik dinosaurs that lie ootdoors cless aves proper, in the broader group avialae, hae bin fun datin back tae the mid-Jurassic period. Mony o thae earlie "stem-birds", sic as archaeopteryx, wur nae yit capable o fully powered flight, and mony keepit primitive characteristics like tuithie jaws in steid o beaks, and lang bony tails.

Birds hae weengs thae are mair or less made dependin oan the species; the ainlie kent groups wioot wings are the extinct moas and elephant birds. Wings, thae evolved fae forelimbs, gie maist birds the ability tae flee, althoogh further speciation haes led tae some flightless birds, anaw ratites, penguins, and diverse endemic island species o birds. the digestive and respiratory seestems o birdsarean a uniquely adapted fur flight. Some doo species o aquatic environments, espeicially the aforementioned flightless penguins, and a members o the deuck fowk, hae an a evolved fur soummin`. Birds, specifically Darwin's finches, played an important pairt in the inception o Darwin's theory o evolution bi naitural selection.

Some birds, especially corvids and parrots, are amang the maist genious ainimals; loads of species mak and uise tuils, and mony social species bygae oan knowledge ower generations, thae is considered a form o cultur. Mony species annually migrate stoatin distances. Birdsaresocial, communicating wi visual signals, caws, and doo sangs, and pairteecipatin in sic social behaviours as cooperative breedin and huntin, flocking, and mobbing o predators. the vast maist folk o doo species are socially monogamous, uisually fur yin breedin saison at a time, whiles fur years, bit seendle fur lee. Ither species hae polygynous ("many females") or, seendle, polyandrous ("many males") breedin seestems. Birds produce affspring bi laying eggs thae are fertilized throu sexual reproduction. Thayre forordinar leid in a nest and incubated bi the paurents. Maist birds hae an extendit period o paurental care efter hatching. Some birds, sic as hens, lay eggs even whin nae fertilized, tho unfertilized eggs dae nae produce affspring.

Mony species o birds are economically important. Tame and wild birds (poutrie and gemme) are important soorces o eggs, bridie, and feathers. Songbirds, parrots, and ither species are popular as pets. Guano (bird darn) is harvested fur uise as a manure. Birds prominently figure oothrou human cultur. Aboot 120–130 species hae acome extinct due tae human activity sin the 17t yearhunner, and hunners mair afore then. Human acteevity threiten aboot 1,200 bird species wi extinction, tho efforts are underway tae pertect thaim. Recreational birdwatching is an important pairt o the ecotourism industry.