Birds.π¦
π¦ Birds Birds are a group of warm-blooded vertebrates constituting the class Aves / Λ eΙͺ v iΛ z / , characterised by feathers , toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart , and a strong yet lightweight skeleton . Birds live worldwide and range in size from the 5.5 cm (2.2 in) bee hummingbird to the 2.8 m (9 ft 2 in) ostrich . There are about ten thousand living species, more than half of which are passerine , or "perching" birds. Birds have wings whose development varies accordi...