Bird

**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 teugh skelet. Birds bide warldwide and range in size fae the 5&nbsp;cm (2&nbsp;in) bee hummingbird tae the 2.75&nbsp;m (9&nbsp;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 sangbirds.

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 flicht, and mony keepit primitive characteristics like tuithie jaws in steid o beaks, and lang banie 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 flichtless birds, anaw ratites, penguins, and diverse endemic island species o birds. the digestive and respiratory seestems o birdsarean a uniquely adapted fur flicht. Some doo species o aquatic environments, espeicially the aforementioned flichtless 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; mony 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 ("mony females") or, seendle, polyandrous ("mony males") breedin seestems. Birds produce affspring bi laying eggs thae are fertilised 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 fertilised, tho unfertilised eggs dinnae produce affspring.

Mony species o birds are economically important. Tame and wild birds (poutrie and gemme) are important soorces o eggs, bridie, and feathers. Sangbirds, 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 threitens aboot 1,200 bird species wi extinction, tho efforts are underwey tae proteck thaim. Recreational birdwatching is an important pairt o the ecotourism industry.

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