The Seven Sages are the Apkallu.
The Dictionary of Deities and Demons in the Bible states that they were servants of Ea, responsible for teaching mankind how to govern and start civilization. They interacted with the ancient kings1, and Gilgamesh is referred to in one "cylinder" as "master of the Apkallu". Additionally,
the seven Apkallu became associated with laying the foundations of the seven ancient cities: Eridu, Ur, Nippur, Kullab, Kesh, Lagash, and Shuruppak.
The entry then confirms that the Apkallu are the Seven Sages mentioned in The Epic of Gilgamesh.
The Assyrian Sacred Tree: A History of Interpretations states that certain depictions of the Apkallu show them having the heads of birds, as well as having wings.
It is possible that the reason the city of Uruk is not included in that entry is that the author of The Epic of Gilgamesh simple borrowed the idea of the Apkallu from other, perhaps earlier, works, and thus it is not consistent with the classical accounts of them.
1 Another book explicitly says that only one Apkallu advised each of seven ancient kings; each one advised in a different "generation", although this does not imply that the Apkallu are related to one another as parents to children. This entire claim differs slightly from other interpretations.