Here is some info from research on Cormorants that provides some background on causes:
"The abnormal rotation of the carpal joint in some of the cormorants in this study is similar to a disease with a variety of names, including angel wing, slipped wing, and airplane wing (Kear, 1973; Kreeger and Walser, 1984; Ritchie et al., 1994)."
"Angel wing occurs in young waterfowl when the weight of the rapidly growing flight feathers on the manus is insufficiently supported by the non-rigid bones of the wing. The manus twists outwards, and remains in that position after the bones are ossified. It has been reported in domestic and wild waterfowl fed by humans, and has been associated with overfeeding, an unbalanced diet, including an excessive level of protein, and deficiencies in calcium, manganese, and vitamin D.
It is found in rapidly growing birds, and occurs more frequently in male birds, in the larger individuals of a brood, and during warm weather, when energy otherwise used to maintain body temperature may be used for growth. [my italics] The only report of an angelwing- like disease in wild birds not fed by humans is in American white pelicans (Drew and Kreeger, 1986). A possible explanation for this disease in cormorants in the wild is very rapid growth. Such growth is most likely to occur in older chicks in the brood, in broods with parents superior in fishing skill, and in years of mild weather and abundant food supply (Dunn, 1976; DesGranges, 1982)."
And link to full article:
http://www.jwildlifedis.org/cgi/reprint/35/2/331.pdf
If you tape, you might consider 3M paper tape (transpore), it is easy to work with and easy to remove.
Thanks for posting (now I know what an airplane wing is...), good luck with those fast growing devils!