渡り鳥
わたりどり · wataridori · JLPT N1 · noun
bird
渡 — water radical 氵 + 度 (measure/cross)
渡 combines the water radical 氵 with 度, which provides the sound and suggests measuring or passing across. Originally it meant to cross a body of water, like fording a river or ferrying across. Over time it broadened to mean 'to pass through' any transition, including time or stages of life.