عَلَيْهِ الطَّيْرُ تَرْقُبُهُ وُقُوعًا.
عَلَيْهِ: prepositional phrase functioning as an advanced predicate relation.
الطَّيْرُ: postponed nominative subject.
تَرْقُبُهُ: indicative imperfect verb; implicit feminine-singular subject referring to collective «الطير»; «هُ» is its object. The clause describes the birds’ state.
وُقُوعًا: expresses the birds’ poised-to-fall state; the printed commentary treats it as a plural of «واقع» serving as ḥāl.
The focus of this chapter remains «بِشْرٍ» as ʿaṭf al-bayān.