What are you feeding them? I've read a lot of different theories on what causes angel wing, including high levels of protein in feed. I still don't know much about it, but I had my ducks on starter probably much longer than they needed. Two of them developed angel wing. As awful as it sounds, I let it go without wrapping since its just a cosmetic issue. For a couple weeks, it gradually got worse. I then switched the ducks over to a grower/finisher (lower protein %) rather than starter and within days both ducks look 100% normal again..no angel wing. Not sure how that's even possible but it's true. I could have just gotten lucky, I suppose. Just a thought.