Practice singing (somewhat like human infant babbling) that begins shortly after songbirds leave the nest. Subsong usually is quiet, garbled, and rambling compared to adult song; it contains some of the same elements, but they are strung together in odd ways. It gradually comes to resemble adult song.
Loose, rambling, quiet song (especially of young birds), often bearing little similarity to full adult song.
an unstructured, often rambling vocalization of low volume heard in young birds and, at the start of the breeding season, in adult birds of certain species.