There are about 10 thousand living types, more than 1 / 2 of which will be passerine, or "perching" birds. Birds have got wings whose growth varies according in order to species; the only known groups without having wings would be the vanished moa and elephant birds. Wings, which usually evolved from forelimbs, gave birds to be able to fly, although further evolution has led to the losing of trip in some chickens, including ratites, penguins, and diverse endemic island species. The digestive and respiratory systems of parrots are also exclusively adapted for air travel. Some bird kinds of aquatic surroundings, particularly seabirds plus some waterbirds, have got further evolved for swimming.
Birds will be descendants of the primitive avialans (whose members include Archaeopteryx) which first appeared about 160 mil years ago (mya) in China. Based on DNA evidence, contemporary birds (Neornithes) advanced in the Center to Late Cretaceous, and diversified drastically around the moments of the Cretaceous? Paleogene extinction event sixty six mya, which killed off the pterosaurs and non-avian dinosaurs.
Many social kinds pass on knowledge around generations, which is usually considered a type of tradition. Birds are cultural, communicating with visual signals, calls, and songs, and engaged in such behaviours because cooperative breeding in addition to hunting, flocking, in addition to mobbing of predators. The vast bulk of bird species are socially (but not necessarily sexually) monogamous, usually regarding one breeding period at a time, sometimes for years, but rarely regarding life. Other varieties have breeding devices that are polygynous (one male using many females) or even, rarely, polyandrous (one female with many males). Birds produce children by laying eggs which are fertilised through sexual reproduction. They are normally laid within a call home and incubated simply by the parents. Many birds have a good extended period involving parental care following hatching