Probably the hardest part you're going to have to deal with is trying to make the feathers, which would probably be best done via textures unless you feel you want to build every single ferrule. Another thing you have to watch out for is how the feathers are laid over each other and how the sizes of feather changes over the body of the bird, as Kris says, we do need to know what sort of bird you're envisioning though.
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