noun
adult bird
Refers to a bird that has reached maturity, as opposed to a chick or juvenile. Used in ornithological and general contexts.
この森では、春になると多くの成鳥が巣を作る。
In this forest, many adult birds build nests in spring.
ヒナと成鳥では羽の色が異なる。
The feather color differs between chicks and adult birds.