Angel wing, also known as slipped wing, crooked wing or drooped wing, is a condition of ducks and geese where the last joint of the wing is twisted and the wing feathers point out, and do not lay smooth against the body.
It is more common in geese and typically in either the left wing or both wings, only rarely in the right wing only. Males develop it more than females. The birds that develop the problem are perfectly healthy, they are just not as beautiful.
Because of the discussions I have heard over the years on the cause of angel wing, I did a search for all research on the subject. The best article was one written by Janet Kear, who is the Senior Scientific Officer of The Wildlife Trust in Great Britain. Some of the researchers feel the condition is genetic, but others have proven it is not. Because she works with waterfowl from many parts of the world, Ms. Kear has come to the conclusion that it is a nutritional problem due to excess feed.
She has found that waterfowl that normally mature in the Arctic environment do not show any angel wing because of their naturally fast growth. It does appear, however, in those species that come from a more temperate environment where they grow slower under natural feeding conditions. But by feeding them unlimited, high protein, high energy feed, they grow unnaturally fast and their wing weight seems to outgrow the strength of the wing to support it, which causes the twisting and resulting angel wing. Further proof of this is from another article that said "If their wings start drooping they are put on a diet of alfalfa pellets (instead of Chick Growena) until the condition clears up."
The only wild waterfowl populations known to be affected are those fed by man. In Sweden, ten different park populations of Canada geese produced angel wing. The following year one flock was not fed any artificial feed and there were no angel wing goslings produced.
Ms. Kear's suggestions are to not feed high protein, high energy feed (such as turkey feed), provide plenty of room for exercise, keep in small groups, provide plenty of grass or green feed and keep the pen dark at night if possible so less eating occurs. If you do notice a twisted wing, however, you can form a sling to hold the wing in place to allow proper development.
If you want more detailed information on Angel Wing or other wing deformities, we recommend and sell a pamphlet by Dave Holderread titled Wing Disorders in Waterfowl for only $7.95.