Adam Clarke on Revelation 8:13

I - heard an angel flying - Instead of αγγελου πετωμενου, an angel flying, almost every MS. and version of note has αετου πετωμενον, an eagle flying. The eagle was the symbol of the Romans, and was always on their ensigns. The three woes which are here expressed were probably to be executed by this people, and upon the Jews and their commonwealth. Taken in this sense the symbols appear consistent and appropriate; and the reading eagle instead of angel is undoubtedly genuine, and Griesbach has received it into the text.