“the birds of the heavens.” The word “heavens” (or “heaven”) is always plural in Hebrew; thus the phrase could be translated, “the birds of the sky.” In Zephaniah 1:3 God mentions much the same things as in the destruction of Noah’s Flood, except this list has “fish,” while Genesis had “creeping things” (Gen. 6:7), and this list adds “stumbling blocks. However, this next destruction will not be by water.
“the stumbling blocks with the wicked.” The Hebrew word can mean “stumbling blocks,” and that seems to make good sense here, although many modern English versions have “ruins” or some equivalent. In the Day of Yahweh, not only will the wicked be destroyed, but also the stumbling blocks that they have created. For example, the idols of Syria caused Israel to stumble (2 Chron. 28:23), and God said that he would destroy the idols (Ezek. 30:13). It is also very possible that it was because of this verse that Jesus said that God would gather both the lawless people, the wicked, and all the stumbling blocks (likely the idols) and cast them into the fire (Matt. 13:41).