The unclean birds are pictures of the demonic. What did Jesus say, where the body is the vultures will gather.

Luke 17:30 "Even so will it be in the day when the Son of Man is revealed.” This is background to the statement which we find in V. 37 And they answered and said to Him, "Where, Lord?" So He said to them, "Wherever the body is, there the eagles will be gathered together."

105 aetos- 1) an eagle (KJV): this could refer to a vulture which resembles an eagle. Job 39:30 speaking of the eagle states “Where the slain are, there is she"

The eagle and the vulture were unclean animals, as is the ostrich, the owl, the seagull, the hawk and its kind, the little owl the corimont, the great owl, the white owl, the Pelican, and the carrion, vulture and the stork, the heron and its kinds, the hoopoe, and the bat.

Remember Abraham had to chase away the vultures when he prepared the sacrifice as God promised him the nations will come from his loins. Gen. 15:11 “And when the vultures came down on the carcasses, Abram drove them away.” In the Desert the carcasses are food for vultures and birds of prey (Deut.28:26; 1Kings 14:11; Ps.79:2)

The nations are gathered at the coming of the Lord in the valley of Megiddo.
Ezek 39:17b"And as for you, son of man, thus says the Lord GOD, 'Speak to every sort of bird and to every beast of the field: "Assemble yourselves and come; gather together from all sides to My sacrificial meal which I am sacrificing for you, a great sacrificial meal on the mountains of Israel, that you may eat flesh and drink blood."

John affirms this in Rev 19:17-18 “Then I saw an angel standing in the sun; and he cried with a loud voice, saying to all the birds that fly in the midst of heaven, "Come and gather together for the supper of the great God,"that you may eat the flesh of kings, the flesh of captains, the flesh of mighty men, the flesh of horses and of those who sit on them, and the flesh of all people, free and slave, both small and great."

So this is not just a saying but describing a literal apocalyptic event as the birds feast on the carcasses of the dead who tried to fight Christ, they are the unclean, the rebellious. It would only be fitting they would be eaten by these birds.