tercel (n.)

"male falcon," late 14c., from Old French tercel (c. 1200), from Medieval Latin tertiolus, from Latin tertius "third, a third," from root of tres "three" (see three). Various theories as to why it is called this; one says it's because the males are a third smaller than the females, another because a third egg in the nest (smaller than the other two) is believed always to produce a male bird.