As a juvenile ( adjective as noun : juvenility ; from Latin iuvenis = teen ') is called in biology and medicine Childhood - and youth stages of the developmental stage of an organism prior to maturity . The juvenile stage is followed by the adult stage. It is preceded by the embryonic stage.
In birds , the plumage that a bird wears in the juvenile stage from flying out to the first moult is called youth plumage . There may be several intermediate steps here before the adult stage is reached; Birds that are no longer juvenile but not yet adult are called immature .