Hi silviapalara - as for folding the wings when not flying you can create a skeleton where the actual bones would be and use bind skin>smooth bind. Make sure you have enough polygons around the area where you wish the bend to be and try to have lines running parralel to the bend. Where the bends get rough you can add lattices. I'm not saying it's a supper easy process but it works the same for large wings as for small wings I've not built a wing like this but I will be shortly. I have animated one and it provided convincing results even tho it was super low poly and crossed the bend area at odd angles.
Check out the subsurfacescattering on my tongue...
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