On Birds
Why did the Holy Spirit descend as a dove? There are a lot of good reasons for this--doves are evocative of the covenant with Noah after the flood; doves are light and gentle creatures and the Holy Spirit alights upon Christ gently.
But I think there's something about birds that is kind of like how there is something about gold. Birds are evocative of spirits, and have been even before Christ. Rome was founded because of a wager about vultures--symbols of the God of War, Mars. After Christ, we have seen the Byzantine and Holy Roman Empires use the two-headed Eagle, almost every country has a national bird, and this practice seems to be ubiquitous. It's not that every country decided--"Hey, we should pick a national bird"--it's that every country had one already, colloquially if not officially.
National birds tell us about the spirit of the country, or the spirit of the organization. America has the Eagle, Canada has the Goose, France has the Gallic Rooster, the Philippines have the Philippine Eagle. You an obviously learning something about a people by the symbols they choose for themselves, but you can especially learn something about a people by the birds they choose to represent them. The birds embody their national spirit.
On Angels
My mind naturally transitioned from Birds to Angels, not only because of the winged imagery but also because I have thought about the spirits of places before.
This thought took a different approach though. When did God create angels? When I googled, the top result was that it was on the first day when God separated the light and the dark. I remember also Hambone telling me about some Tolkeinology that prior to creation the angels sang in a harmonious chorus. There's something convincing about both ideas.
The idea that Angels were created on the first day is convincing because it establishes quite neatly that nothing existed prior to creation--that everything is accounted for in Genesis. While the creation of Angels are not explicit, I think it could easily be implicit. Aquinas notes--as a helpful commenter here once told me--that the Angels are so numerous as to be beyond human comprehension. Angels could have jobs and those jobs could be things like "Carry the sun" or "Carry the moon" or "enforce the division between light and dark". The separation of the light and dark could also be evocative of the fall of angels--fallen angels were separated from the light and were cast into the outer darkness. Both ideas could be correct as far as I can tell.
I like the second idea--that Angels pre-existed Genesis--because it implies that God created Angels and while I am sure He found them very good, they were not His finished work. The Angels could adore and glorify God alone, but in the plan of creation is something more mystical and beautiful than just the formless void and the angels alone. There's something beautiful about that thought--that God could have contented himself with angels but didn't, because he intended creation from the very beginning.
Also, the idea of an Angelic genesis is kind of cool. Although--God is creating Angels all the time, I think, so it is never a complete genesis, the way Biblical Genesis is complete. Maybe that's why Angels are not mentioned, and yet are presumed to already exist (as Satan is a fallen angel and already in the garden.)
I don't know what the Church teaches on Angels, having--as always--done no research for this. I also don't know how detailed knowledge of the Angelic genesis would help with our faith journey, but I did find the thought interesting and I hope you do too.
Ad Jesum Per Mariam