The Avians are and offshoot winged typed human and were once slaves to the Y'Lyntians.
History 2003 Series
When the Y'Lyntians held domination over the Earth, they enslaved other humans. Those who were not suited for certain tasks were mutated by the power of the crystals. The Avians were among them and were given wings to left heavy loads and to keep dissident Y'Lyntians who tried to escape the island. The Avians were kept in a floating cage so that they would not foul up the purity of Y'Lyntian air. But when the other humans cultures rebelled, that resulted in the destruction of the Sun Crystal, the Avians freed their cage from its surface anchor and retrieved a few fragments of the crystal, enabling their city to stay in the air and turning a prison into a home.
But after a long isolation, many Avians believed they could conquer the surface, not hide from it. The most radical of Avians, Mephos, led an uprising that eventually resulted in him being defeated, banished to the surface, stripped of his wings. Raptarr kept an eye on him to make sure that he would do no damage. But Mephos manage to construct himself mechanical wings and stole Raptarr's crystal diadem, which would allow him to locate the city. He joined up with his remaining followers, who had captured the Council Chamber. Mephos intended to use the power of the city's crystal as a devastating weapon to conquer the surface, but Raptarr and the Turtles defeated him and he was once again stripped of his wings, but this time imprisoned in the city.they eventaily join human socity and coexist by the time of the pan galactic alliance and the home is know a major base for the earth's stationed Pan Galactic Alliance millitry for there areo space force and there areo space navy