Ah, this one. I kind of stopped this one a while back after I realized I didn't have enough knowledge to ponder how such a "different" world would develop.
As this POD is too far back for accurate predictions of what " this society" would be relative to ours, but now that it's been brought up, I have been thinking about what culture would be like in a world with more than one sentient species.
Religious and Philosophical worldview
Initially, as with OTL, religion generally begins with animism, fear of the unknown, and superstition. A tribe fears what forces of nature are bigger, stronger and greater than it. Volcanoes, floods and quakes may be seen as evidence of some spirits or supernatural forces are at work. Living among nature makes one fear, and venerate it as god(s). Later on, as agriculture and civilization develops, and we become more organized, in law, in trade, in life, there is reduction in dependency and fear on nature and superstitious view of its inner workings, and animism falls out of favour as explanation.
By now, people (and in TTL, parrots) will have progressed either to a codified religion or philosophy, whether it be pantheism, polytheism or monotheism.
Now, to the analog of the 'Axial Age' of TTL.
A religion reflects what social and environmental conditions a group developed in. Now birds, strongly visual and auditory learners as well as mobile creatures, have, from their jungle nature to the advent of civilization, constructed their own worldview to explain the meanings of life and everything.
Living in the rainforests have given the birds a panoramic view of the landscape. They can fly, twist and turn at will through the trees, seeing flowers and fruits flash by in a kaleidoscope of colours.
A generalized religious view developed as birds developed society, that the universe is a realm extending in a near infinity of directions, up, down, around, in every nook and cranny lies countless beings, landscapes and worlds and that what we see of it is only but a slice of the reality that surrounds us all.
According to the parrots, we ought to all "open" our eyes and see as much as possible to get closer to the truth. Colour and light is their metaphor for truth.
There is a hierarchy in this worldview. The lowest things, barely above plants and inanimate matter, are the beings they call "The Blinds and Unfeelers" who cannot see or sense much. These are the mindless worms, lizards and tiny critters ignorant of the truth for they cannot move much, but are limited in one-dimensional crawling and tunneling. Most numerous are these beings. Next are the "Half-Blinds and Shade dwellers", the "brute animals" as we would call them. All the wild creatures who roam, in herds, packs and alone on foot as well as non-sentient birds are creatures who live life seeing barely a sliver of the beauty and splendor of the divine. They go through life more or less, still unfeeling and ignorant. The "Light viewers" are the humans who can see the beauty and divineness through things like love, morality, knowledge and hope. The live in societies and through living with each other guide one another closer to the truth. The "Kaleidoscope eyes" the parrots themselves, who believe that they are like humans but perhaps even a bit higher. The parrots believe they see more, know more, and feel more emotion, although just a bit more, than us. The "Top worlders" would be what we call angels or gods to the parrots. The Top worlders can see millions of worlds and colours invisible to us. They also live in a higher dimension above us. They feel more emotions, sense more, and know more than us. What they do in their realm cascades down on us. For example, their tears cause our rain etc. Their breathing causes the wind. The Top worlders are invisible to us. Lastly, there is what the parrots call the "Seer of Infinite Realms"; it would be their analog of "God", "Brahman" or the Infinite.
Now, most of the bird philosophies branched from this world view, but diverged as one society believed one thing or another and their worldview began to diversify.
*By the way, I just made up the names of the bird personages. It's really just whimsical
The Emotional Ones- Living in the foothills of the tropics, many of the Garudas and Australians/New Guineans believe in living a holistic, socialist-like lifestyle. They see all things as one whole and believe in a pantheism. They are non-violent in nature and believe in harmony by sharing food, resources, and looking out for each other. They are strongly sensitive to each other's feelings and are very sentimental, poetic and contemplative. Like the analog of certain New Age groups, the emotional ones may reject organized, codified religion, and focus on personal spirituality. But they also honour figures like Yriitriiyeeryeria who was said to be TTL's version of the Buddha. This worldview is also found in Central Africa and South Africa where the settled later on.
The Logical ones- In Australia, a belief system developed where pragmatic but individualistic farming birds developped logic and philosophy. Their worldview was like a combination of Greek rationalism with Confucianism. They had made many contributions to law and medicine.They, from their experience with tools, machines and civilization, developed many complex mathematics, setting the stage with collaboration with man to set the stage for the industrial revolution. Notable was the bird
Krayaiaw Srrriio Srriii who was credited with developing the scientific method independently of human society and Siuiura Kaimamatretretre who was the first to start to try and formulate laws of physics, including what we call Newtonian mechanics.
The Noble Ones- The Tengus and a few Garudas follow the beliefs of honour and shame. They have developped religious sects similar to Abrahamic religions however, in which the watchful eye of the "Infinite Seer" demands total submission to those under his infinite skies, with focus on absolute moral codes, devotion and total willingness to die for your beliefs. The Leader of the Flock mentality is also very strong here where one certain group, the sect of the "Shining Feathers" believe that the Infinite Seer has a prophet, such as the prophet Keeoer Keieer Argririrara... who lead that tribe of Tengus to conquer land as far west as the Caucasus, and repelled later waves of invaders, mainly other Tengus, as well as Pakistani Garudas that tried to settle there. Others consider Keeoer Keeier Argaririra a devil, demon or idol, and believe that oh, say Saeaiaghayaiaear, the mighty, is the true Messiah. The Pakistani Guradas, have a warrior culture similar to the Sihks of OTL. Strongly idealistic, The Noble Ones spread their culture lately to southern North America, the Mediterranean and also South America, where passionate religious belief dominates the political scene.