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Description of AvesAves is the latin name for the birds - feathered, winged, bipedal, warm-blooded, egg-laying, vertebrate animals with evolutionary origins among the reptiles. The taxon has been historically treated as equal to fish, amphibia, reptiles and mammals, but in order to make classifications reflect evolutionary history, they are now more usually regarded as falling inside the Reptilia. Around 10,000 living species makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from the 5 cm Bee Hummingbird to the 2.75 m Ostrich. The fossil record indicates that birds evolved from theropod dinosaurs during the Jurassic period, around 160 million years (Ma) ago. Birds are the only clade of dinosaurs to have survived the CretaceousâPaleogene extinction event 65.5 Ma ago.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. Wings are evolved forelimbs, and most bird species can fly; exceptions include the ostriches, emus and relatives, penguins, and some endemic island species. Birds also have unique digestive and respiratory systems that are well suited to their flying needs. 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 transmit knowledge across generations. Many species undertake long distance annual migrations, and many more perform shorter irregular movements.Many species are social and 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, and rarely for life. Other species have polygynous (\"many females\") or, rarely, polyandrous (\"many males\") breeding systems. 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 120â130 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.