fly the coop

From fly, to flee or run away, + coop, an enclosure for birds.

fly the coop (third-person singular simple present flies the coop, present participle flying the coop, simple past flew the coop, past participle flown the coop)

1. (idiomatic) To depart hastily or unannounced; to escape or flee.
   • 1910, William MacLeod Raine, chapter 3, in A Texas Ranger:

     Not liking the accommodations, I took the first chance and flew the coop.

2. (of a bird) To escape from a pen or similar enclosure.
   • 1961 January 6, “Assisi Revisited”, in Time:

     Explained a Curtiz assistant: "We had three ravens in Assisi; one died of cold, and another flew the coop."

• Usually used in the simple past form.