Birds (Aves) are a group of endothermic vertebrates, characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a lightweight but strong skeleton. Birds live worldwide and range in size from the 5 cm (2 in) bee hummingbird to the 2.75 m (9 ft) ostrich. They rank as the class of tetrapods with the most living species, at approximately ten thousand, with more than half of these being passerines, sometimes known as perching birds or, less accurately, as songbirds. COUNT 5
QSN1 What is a group of endothermic vertebrates characterised by feathers and toothless beaked jaws? ANS1 Birds QSN2 What is the smallest bird? ANS2 bee hummingbird QSN3 What is the largest bird? ANS3 ostrich QSN4 What is the size of the smallest bird? ANS4 5 cm (2 in) QSN5 What is the size of the largest bird? ANS5 2.75 m (9 ft)