In this sentence, "rōvī" can only refer to the birds because the "ī" at the end of "rōvī" shows agreement with a plural+accusative noun. This matches the case/number of "hontī", while it only matches the number of "Ābri" without matching the case.
E.g. "Ābri rōvī hontī ojehikis." = The women bless the large birds
"Ābri rōvi hontī ojehikis." = The large women bless the birds