(also fledgeling)

a young bird that has just fledged.

飛ぶことを習い始めた, 羽の生えたばかりの〈ひな鳥〉

usually as modifier a person or organization that is immature, inexperienced, or underdeveloped:

できたばかりの〈組織･システムなど〉; 駆け出し［経験不足］の〈人〉, 青二才

e.g. the fledgling democracies of eastern Europe.

mid 19th century: from the obsolete adjective fledge (see fledge), on the pattern of nestling.