Angel Wing in Waterfowl


As much as we think we know about a given subject, we can be sure that there is always someone out there, somewhere, that knows more. Birders are no exception and any of us who spend time with our noses in books or perusing the numerous blogs and forums dedicated to birds will eventually uncover some information tidbit that is entirely novel.

Such was the case when this writer happened upon a curious picture of a Muscovy Duck with a wing feather pointing away from it’s body. The poster of this picture also thought it was strange that one feather was not sitting flat, neatly aligned with the other primaries of the closed wing, and posted it asking if anyone could tell what was up with this odd duck. Birders on the Internet tend to be an extremely helpful lot that love to share knowledge, so it was no surprise that this appeal for information got an immediate response. The savior said quite simply that it looked to be a clear case of Angel Wing, which is thought to affect only waterfowl, mostly ducks and geese, and primarily occurs in domesticated animals.


Birds suffering from this affliction have a wing that is twisted at the terminal joint, causing one or more primary feathers to stick out. It is thought to be incurable and often only affects one wing, usually the left wing for some unknown reason. Angel Wing is known to manifest in younger birds, and apparently males are more prone to developing it than are females. Although it seems that very little research has been conducted on this condition, there appear to be two competing ideas for what causes it.

The first is that it is a rare genetic anomaly, or that there is at least some genetic component, as it has been observed through several generations of offspring derived from the same breeding pair. The second theory has to do with a bird ingesting too many calories and getting too much protein and/or sugar in its diet. Inappropriate levels of vitamin D, vitamin E and/or manganese in a given bird’s diet may also be to blame.


Whatever the proximate cause(s) may be, it appears that during a young bird’s development, the wrist joint grows at a slower rate than the rest of the wing, causeing it to twist out. The result of this differential growth rate is that one or more feathers attached to the terminal wing bone end up sticking out from the body when the wing is folded, rendering the bird unable to fly. Flightless may not pose a major problem to domestic birds, but Angel Wing in wild birds is often a death sentence. Luckily the only wild populations known to be affected are those that come in close contact with humans that feed them. So, if the inappropriate diet theory is correct, there is hope to eliminate it in wild birds if people are informed enough to desist feeding waterfowl human food like bread or popcorn and switch to duck seed that is engineered to provide the right balance of nutrients.




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