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to leave the nest
to go out into the world; to become independent (of one's parents); to graduate (and become a member of society)
5月末、最後のツバメが巣立った。
At the end of May, the last swallow chick left the nest.
カラスの雛が今朝、次々と巣立っている。
The crow chicks are leaving the nest one by one this morning.
毎年初夏、庭の物置からスズメの雛が巣立つ。
Every year in early summer, young sparrows leave the nest in the garden shed.