For it shall be, that, as a wandering bird cast out of the nest, so the daughters of Moab shall be at the fords of Arnon.
As a wandering bird cast out of the nest - rather, 'as wandering birds, a brood cast out' (in apposition with "a wandering bird," or rather wandering birds); namely, a brood just fledged and expelled from the nest in which they were hatched (Horsley) Compare Isaiah 10:14; Deuteronomy 32:11.
(So) the daughters of Moab - i:e., the inhabitants of Moab. So 2 Kings 19:21; Psalms 48:11; Jeremiah 46:11; Lamentations 4:22 (Maurer).
Shall be at the fords of Arnon - trying to cross the boundary river of Moab, in order to escape out of the land. Ewald and Maurer make "fords" a poetical expression for 'the dwellers on Arnon:' answering to the parallel clause of the same sense, "daughters of Moab."