词源不详。
Middle English, in which bird referred to various young animals and even human beings, may have preserved the original meaning of this word. Despite its early attestation, bridd is not necessarily the oldest form of bird. It is usually assumed that -ir- from -ri- arose by metathesis, but here, too, the Middle English form may go back to an ancient period. [Liberman]Figurative sense of "secret source of information" is from 1540s. Bird dog (n.) attested from 1832, a gun dog used in hunting game birds; hence the verb (1941) meaning "to follow closely." Bird-watching attested from 1897. Bird's-eye view is from 1762. For the birds recorded from 1944, supposedly in allusion to birds eating from droppings of horses and cattle.
A byrde yn honde ys better than three yn the wode. [c. 1530]