Bird

Birds are a group of warm-blooded vertebrates constituting the class Aves, 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 smallest to the biggest from the 5.5 cm (2.2 in) bee hummingbird to the 2.8 m (9ft 2 in) ostrich. There are about ten thousand which ranks them as the class of tetrapods with the most species.

Etymology
The word "bird" comes from Middle English brid which comes from Old English bridd of unknown origin and relation. It is perhaps a substrate from a small surviving pocket of people who spoke a language before the Romans and the Celtic migrations.