The term translated here as eagle
appears also in Jesus’ address about the destruction of Jerusalem (Matthew 24:28). There the term is translated as vulture.
Eagles and vultures alike consume dead meat. The picture would be that the first four trumpets produced much death, which gave the birds of heaven a feast (see Revelation 19:17–21). One of these carrion birds, though surrounded by so much to eat, must advise the remaining two‑thirds of humanity that worse is yet to come.
13 Then I looked, and I heard an eagle crying with a loud voice as it flew directly overhead, “Woe, woe, woe to those who dwell on the earth, at the blasts of the other trumpets that the three angels are about to blow!”