«إِذَا أَنْكَرَتْنِي بَلْدَةٌ أَوْ نَكِرْتُهَا / خَرَجْتُ مَعَ الْبَازِي عَلَى سَوَادِ»
If a town rejects me, or I find it unfamiliar, I depart with the falcon under cover of darkness.
The prepositional expression ʿalā sawādin conveys the setting and manner of departure and appears without circumstantial wāw. The adverbial relation naturally attaches it to the act of leaving. This should not be summarized merely as deletion of wāw from a nominal sentence: the grammatical question is which governing element the prepositional phrase qualifies.