Intelligence doesn't require opposable thumbs. Civilization does require multiple species.
When thinking about animal intelligence, it’s hard to keep our biases out of it. There’s a tendency to apply the human evolutionary story living in many of the answers to this question. That’s not unreasonable. Humanity seems like the most intelligent species and the only material culture we know of. Some evidence beats no evidence.
Many of the answers I’ve read for this question either assume alien
races must be primate analogs or that flying creatures can’t become
I think it’s pretty obvious you are looking for an flying alien race for a story that is comparable to humans or a civilization that is comparable to ours. Before I address these possibilities, let me dive into human evolution to look at the evolution of intelligence.
I often hear confusion about human evolution. “Post hoc ergo proctor hoc” is Latin for “after this therefor because of this.” It represents the common logical fallacy that sequence alone proves causality. In this case, that because reasoning intelligence is necessary to produce civilization, tool use must be in place to allow the development of higher intelligence. Or that civilization requires a reasoning intelligence because humanity had it before we civilized. My only point here is this, apes evolved a high order of intelligence for reasons that had little to do with the ultimate utility of having intelligence — such as civilization. So there’s really two questions here.
- Why did a few animal species evolve a high order of intelligence?
- How did civilization evolve for homo sapiens?
First, there are many intelligent animals with new research revealing more all the time — pigs, octopuses, bears, parrots, etc. But there’s general agreement that the big three are the great apes (which includes humanity), elephants (several species past and present), and dolphins (including killer whales).
Looking at these three animal groups, it’s difficult to find common patterns. Dolphins are predators; elephants are herbivores, and apes are either herbivores or omnivores. Elephants and dolphins don’t really use tools and dolphins clearly lack any kind of manipulative appendage. One group is semi-arboreal, the other land based, and the third aquatic. Non-human apes are polygamous, elephants matriarchal, and human relationships are too varied to easily pin down — dolphins too actually. And only humans have forward facing eyes.
The commonalities that do exist are the possession of a large, complex brain, a high metabolism, a long life span, and extremely complex social structures - not to be confused with merely being a social species. In fact, social species are among the most stupid animals; consider the social insects.
Humans, chimpanzees, and dolphins in particular posses what are called fission/fusion relationships. This means treating other individuals alternately as friend or foe depending on both the immediate and long term advantage. Social species treat each other consistently as friends. Individualistic animals compete with each other openly, almost as opposing species. But only apes and dolphins could ever indulge the axiom of, “the enemy of my enemy is my friend” or “politics makes strange bed fellows.”
It seems the evolution of politics drives the development of higher
reasoning intelligence. Why? Because it requires not just self
awareness, but the ability to predict the behavior of other
individuals, to walk in their shoes, so that you can deceive them.
A chimpanzee in a zoo, given a banana, won’t simply hide the banana to avoid sharing it, it will alter its behavior to appear as if it doesn’t have a banana when other chimps are looking. This requires the chimp to calculate how its behavior appears to other chimpanzees. It is a lot more cognitively challenging to lie effectively than use a tool.
What’s germane to the possibility of intelligent birds is this. While I don’t believe science yet has a handle on exactly why a few species have evolved politics, all that appears required is a large brain, a long life of experiences, and some reasonably sophisticated means of communication. By that measure, almost any animal type imaginable could conceivable evolve reasoning intelligence.
As for the development of civilization, it might be worthwhile to consider what a long shot that was all by itself. Homo Sapiens existed for almost 100,000 years before they developed beyond stone age tribes. Considering too that since we now know Homo Sapiens successfully interbred with Neanderthals (I’m 1.7% myself) we must consider them more or less the same species. Thus human intelligence existed on Earth for hundreds of thousands of years without civilization appearing. It was only after the end of the last ice age, that conditions in a few places put our ancestors next to a few useful species of plants and animals thus making agriculture possible.
Agriculture and animal husbandry both are not inventions in the modern sense, but rather symbiotic relationships - another evolutionary process. Local conditions must be sufficiently variable to drive an evolutionary solution to stabilize the variability — to the mutual advantage of two species (humans and wheat for example), but not so difficult (ice age tundra) that an early evolutionary experiment at cooperation couldn’t possible succeed.
Simply put, civilization doesn’t belong to humanity alone, but also to
wheat, rice, corn, dogs, goats, chickens, and cattle. If all these
species hadn’t evolved together, all humans would still be living in
caves — no matter how clever and devious we are.
Thus if you’re looking for your avian species to have material civilization, broaden your thinking out to the planet they live on and the other species they partner with. What geological or climate forces caused the symbiotic coevolution of civilization with one intelligent, political species (the birds) in the drivers seat, but others equally important?
P.S. Nobody mentioned parrots. They’re intelligent, arboreal, long lived, have opposing digits, and are great at communication.