The anatomical and physiological mechanisms underlying the production of bird song, the acquisition of song during the life of individual birds, the acoustic structure of the songs, and their adaptive function in the social life of birds, have been the subject of intensive scientific study.
It has been known since time immemorial that the songs of different species vary, and are more or less characteristic of the species. Species vary greatly in the complexity of their songs and in the number of distinct kinds of song they sing; in some species, individuals vary in the same way. In a few species, however, for example starlings, songs incorporate arbitrary elements learned in the individual's lifetime, a form of mimicry. In many species it appears that although the basic song is the same for all members of the species, young birds learn the details of their songs from their fathers, and this allows variations to build up over generations, a form of dialect.
Major functions of bird song include intra-specific recognition, especially in advertising for mates, and defending territory.
Bird song is often imitated in music, especially song, and is also a popular subject in poetry. Famous poems inspired by bird song include Shelley's To a Skylark ("Hail to thee, blithe Spirit!/Bird thou never wert") and Gerard Manley Hopkins' Sea and Skylark.