Angel wing is a musculoskeletal deformity in waterfowl, ducks and geese most notably, that comes of dietary imbalance during thier initial growth stages - its associated with both high carb diets (people throwing bread to birds in ponds) and very high protein diets (using turkey or game bird feed over 24% protein), though the exact mechanism isn't fully understood, and clearly has a genetic component besides.What is Angel Wing?
Basically, it causes the wing joint to twist outwards, rendering the birds incapable of flight, and tends to be more pronounced on one side than the other.