It's important to figure out exactly where the blood is coming from. This will help you figure out how to treat it.
For example, if a pin feather has been broken, the bleeding may not stop on it's own, and that would require extra steps.
I really hope someone else jumps in here, because I don't think it's normal at all. Maybe if you change the title of your thread to include the word blood or bleeding as well as the word duckling (that way they know it's a little baby), it will bring in more experts. The breed probably isn't related to the problem, so you could remove that. Something like "Help - duckling bleeding under wing, skin is irritated" or "Help - duckling bleeding under wing (with pic)"
Good luck!!!