Ythrians and Comments.
On Earth, manipulation and cooperation generated intelligence. Manipulating the environment led to thinking about it. Cooperation became linguistic and thus generated abstract thought. How did intelligence arise on Ythri?
"...the feet acquired more and more ability to seize prey and manipulate objects." (Rise Of The Terran Empire, p. 483)
A drought forced ornithoids:
"...out of dwindling forests into growing savannahs. There they evolved from carrion eaters to big-game hunters in a manner analagous to pre-man. The original feet became hands, which eventually started making tools." (ibid.)
There was hunting but no gathering so the cooperation remained at the level of the immediate kin group:
"...the intelligent Ythrian remained a pure carnivore. Typically, primitive hunters struck from above, with spears, arrows, axes. Thus only a few were needed to bring down the largest beasts. There was no necessity to cooperate in digging pits for elephants or standing shoulder to shoulder against a charging lion. Society remained divided into families or clans, which seldom fought wars but which, on the other hand, did not have much contact of any sort." (pp. 485-486)
So how much language would develop in those conditions? But more happened: not an agricultural revolution but a herding revolution. Herding, then domestication, of maukh and mayaw stimulated the invention of skids, wheels etc, making it easier for Ythrians, awkward except in flight, to move around on the ground. Also, agriculture, invented to provide fodder, generated a food surplus that supported travel, trade, cultural intercourse and larger, more complex societies although the mobility of flight made cities and thus "civilizations" unnecessary.
So maybe all that does explain how the Ythrians became intelligent?