Angel Wing also known as Slipped Wing, crooked wing, or drooped wing is a disease that affects waterfowl, primarily geese and ducks, in which the last joint of the wing is twisted with the wing feathers pointing out laterally, instead of lying against the body. Males develop it more than females.
The disease manifests as an incurable anatomical condition which is acquired in young birds. Due to a high-calorie diet, especially one high in proteins and/or low in vitamin D, vitamin E and manganese, one or both carpus (wrist) joints are retarded in their development relative to the rest of the wing; for reasons unknown, if only one wing is affected it is usually the left one. The result is a wrist which is twisted outwards and unable to perform its usual function. Angel wing symptoms include stripped remiges (flight feathers) in the wrist area, or remiges protruding from wings at odd angles. In extreme cases, the stripped feathers may resemble sickly blue straw protruding from wings. In adult birds the disease is incurable and usually leads to an early death as affected birds are rendered effectively or totally flightless. In young birds wrapping the wing and binding it against the bird's flank, together with feeding the bird a more natural diet, can reverse the damage.
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.
There are currently two basic theories concerning the cause of Angel Wing:
As little research has been done on this, it is currently impossible to favour one theory over the other.