>>14925834Birds are a group of warm-blooded vertebrates constituting the class Aves /ˈeJviːz/, 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 5.5cm (2.2in) bee hummingbird to the 2.8m (9ft 2in) ostrich.
