The nice thing about confusing metaphors in the Bible is that usually if you just keep reading it will explain its own imagery for you. The Lord describes a great eagle with splendorous, colorful plumage. It comes to a cedar of Lebanon and removes the top-most branches and takes them to a trade city. Then it plants a seed in the land, cares for it and waters it, and it sprouts into a spreading vine. However, in spite of the good soil and water it received from the eagle, the vine started reaching out toward a different eagle to get. Because of this disloyalty, the vine will be rooted up and wither away.
What does this mean? The Lord explains: the first great eagle is Babylon and the top of the cedar is the king and the upper crust of Jerusalem that were deported earlier. The vine is the king of Judah that Nebuchadnezzar set up in their place to be a vassal to Babylon. However, the new king sought aid from Egypt, the other eagle, and now he and his rule will be destroyed.
By Your grace we received wisdom and understanding.