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There are about 10 thousand living species, more than half of which happen to be passerine, or "perching" birds. Birds have got wings whose enhancement varies according to species; the only known groups with out wings are definitely the wiped out moa and elephant birds. Wings, which evolved from forelimbs, gave birds the opportunity to fly, although further evolution has directed to the loss of flight in some parrots, including ratites, polar bears, and diverse endemic island species. Typically the digestive and the respiratory system systems of parrots are also distinctly adapted for flight.http://lovejuxian.com/home.php?mod=space&uid=289958Some bird types of aquatic environments, particularly seabirds plus some waterbirds, possess further evolved intended for swimming.Birds are descendants of typically the primitive avialans (whose members include Archaeopteryx) which first made an appearance about 160 thousand years ago (mya) in China. In accordance with DNA evidence, modern birds (Neornithes) advanced in the Midsection to Late Cretaceous, and diversified considerably around the moments of the Cretaceous? Paleogene extinction event 66 mya, which murdered off the pterosaurs and everything non-avian dinosaurs.http://p4tkipa.kemdikbud.go.id/forum/member.php?action=profile&uid=510703 http://wx2.jjcbw.com/home.php?mod=space&uid=955465Many social varieties pass on knowledge throughout generations, which is considered a sort of tradition. Birds are interpersonal, communicating with image signals, calls, and songs, and taking part in such behaviours since cooperative breeding in addition to hunting, flocking, plus mobbing of predators. The vast bulk of bird varieties are socially (but not necessarily sexually) monogamous, usually intended for one breeding period at a period, sometimes for decades, but rarely with regard to life. Other varieties have breeding devices that are polygynous (one male with many females) or perhaps, rarely, polyandrous (one female with many males). Birds produce kids by laying ovum which are fertilised through sexual reproduction. They are typically laid in the home and incubated by the parents. Most birds have the extended period of parental care following hatching