birds (from wikipedia)

Birds (class Aves) feathered, winged, bipedal, endothermic (warm-blooded), egg laying, vertebrate animals. With around 10,000 living species, they are the most speciose class of tetrapod vertebrates. All species now belong to a subclass of Neornithes, and inhabit ecosystems across the globe, from the Arctic to Antarctica. Birds exist in a variety of sizes from 5 cm (2 in) Bee Hummingbird 2.75 m (9 ft) Ostrich. The fossil record indicates that birds appear in theropod dinosaurs during the Jurassic period, about 160 million years (Ma) ago. Clade paleontologists regard birds as the only dinosaurs to have survived the Cretaceous-Paleogene from extinction event 65.5 Ma (million years) ago.Modern birds are characterized by feathers, beaks without teeth, put crusty eggs, high metabolic rate, a four-chambered heart, and a lightweight but strong skeleton. All living species of birds have wings-the most recent species without wings MOA, which is generally considered to have become extinct in the 1500s. Wings evolved forelimbs, and most bird species can fly. Birds fly, including ratites, penguins, and a number of various island endemic species. Birds also have unique digestive and respiratory systems are highly adapted for flight. Some birds, especially corvids and parrots, are among the most intelligent animal species; several bird species have been observed manufacturing and using tools, and many social species exhibit cultural transmission of knowledge across generations.Many species undertake long distance annual migrations, and many more perform irregular movement is shorter. Social birds, they communicate using visual signals and through calls and songs, and participate in social behaviors, including cooperative breeding and hunting, interested, and mobbing of predators. The majority of bird species socially monogamous, usually for one breeding season at a time, sometimes for years, but rarely for life. Other species have polygynous ("many females") or, rarely, polyandrous ("many males") breeding systems. Eggs are usually laid in nests incubated by the parents. Many birds have extended 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 fertilizer. Birds figure apparent in all aspects of human culture from religion poetry popular music. About 120-130 species have become extinct due to human activities since the 17th century, and hundreds more before then. Currently about 1,200 species of birds threatened with extinction by human activities, though efforts are underway to protect them.