Do you think angels moult their feathers? Just imagine one of the other Archangels popping into Michael's office and seeing feathers everywhere because she's moulting.
I actually do think angels moult their feathers, but it’s probably on a continuous basis, as well as a seasonal big moult, like birds have. With that said, though, I don’t know how often that season would be - most actual birds moult once a year or more, but I imagine angels would be a bit different.
So like, when you have your feathers on wings, what’s happening is that they’re constantly wearing out and being replaced, just like hair is - new feathers grow in the place of the old ones, and one of the big centres for wing grooming is in removing feathers that are old or dirty or that have gotten bent and letting the new ones grow in.
That’s also why preen oil (which in wing fic is usually called wing oil, and secreted from the base of the shoulders, but in actual birds is secreted from the uropygial gland at the base of the tail, is so important - the specific point of the oil depends on the birds (e.g. water birds would have a different base than land birds, but it depends on bird size, location, etc), but all kinds of different birds secrete it. So if you ever have a bird thump against or land on your windscreen or your window, you’ll sometimes see the greasy mark they’ve left with the marks of their feathers, and that’s from the preen oil.
There are a few different reasons for that oil, like… For some it contains pheromones, so for mating and courtship reasons (for fanfic purposes, you can use that to explain the scent of wings etc); for some it’s for general feather moving so like… To basically put everything neatly in its place?
If you look at a feather:
See how it’s not just one unit, but lots of individual fibres, called barbs, running along the quill? Part of the purpose of preen oil is to allow birds to easily put all those fibres back into the position they should be in, for the best aerodynamic flow - if you pick up a feather on the ground, sometimes you’ll see that all of the barbs are facing different directions rather than running all smoothly in the same direction, which is a mess for the wings, but if you have a little grease, just as if you were trying to push your hair into a certain position, you have an easier time fixing it.
Then you have like… So the oil can make it more difficult for mites and similar little parasitic bugs to catch hold, and oil could also be important for waterproofing purposes, like in swans or other water birds.
Flamingos actually secrete coloured preen oil, and so when they apply it it gives them a brighter pink colour? So they usually add that bit of make-up in certain spots to brighten up the feathers.
So on top of the wing oil and the basic expectation of different kinds of feathers, like your primaries, coverts, alulas, scapulas, etc, I’d also generally expect from well-written wings to see like, the regular moulting of feathers, but with the big moult, like…
So birds look SO GROSS when they moult, and it’s hilarious. Some birds actually end up flightless during their moulting period, but generally they all look a bit grim and tend to be a bit more clumsy and vulnerable, so they’re normally close to home and that. Big swathes of feathers all come out, but it’s a drawn-out process that takes a while, and birds usually help it along by plucking out the feathers that need to go, but they obviously need to keep most at a time? They can’t just walk around completely bald, like, they’d freeze to death.
As you can imagine though, it takes a huge amount of like, food and stored-up energy to go through a wing moult because they’re taking off a good fraction of their body and then growing it back, so it normally happens post-breeding season, once the important stuff (fucking and laying eggs) has been gotten out of the way, and like…
That’s an extremely funny concept, honestly. The angels finally fuck and then trigger this utterly miserable moulting period.
One of the cool things in wing fic is that you can go with a lot of different directions, but I admit, one of the most disappointing things about the GO fandom tendency for me is how like… Non-material wings are, and how interesting body building is abandoned to instead make up more spiritual ideas of like, reaching into someone when you touch their wings, et cetera, which I just find to be a bit dull. Not a cop-out, per se, just that when everyone’s like “oh, you’re reaching into his spirit by touching his wings!” it just feels like people are trying to ignore how wings would actually be set up on a person.
