渡り鳥
わたりどり · wataridori · JLPT N1 · noun
bird
🐦 渡る (wataru) = cross over + 鳥 (tori) = bird: a bird that crosses over vast distances with the seasons
The verb 渡る means to cross or traverse, the same root as 渡し船, the ferry that crosses a river. A 渡り鳥 crosses whole continents as the seasons change, which is why English calls it a bird of passage.
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.