@MrsMitford3 I think there’s some confusion here. I read the entire scientific paper that I took the photo I shared from; I didn’t just Google it and think “job done.” But this was my fault for not including a source, and I’m sorry about that. Also, in his statement, the Swan Marker says, “While bread may not be the best dietary option for swans compared to their natural food such as river weed, it has become a very important source of energy for them, supplementing their natural diet and helping them to survive the cold winter months when vegetation is very scarce.” So yes, if it’s an option of you feeding an adult swan bread in winter or them starving, then the risk of “inappropriate diet” is higher from food shortage than from bread. And it’s not just angel wing that’s the problem. Someone else mentioned bread causing algae bloom, and here’s a link about that, from a government website:
https://www.nelincs.gov.uk/keeping-our-area-clean-and-safe/say-no-to-bread-for-ducks/
According to the scientific paper, angel wing is caused by dietary deficiencies - but this can either be a food shortage or too many carbohydrates (the issue is excess calories or filling up without vitamins, like eating white bread) or lack of vitamins apparently (again, can be caused by filling up on nutritionally deficient white bread). They have observed angel wing in wild populations with no human contact (boobies on Clipperton Island) but there HAD been a period of food shortage. So, angel wing is a deformity caused by inappropriate diet (there doesn’t seem to be a whole lot of argument on this?). But there is apparently disagreement, even amongst experts, of what the worse “inappropriate diet” is, based on the fact that I can provide evidence from ornithological organizations (see sources) that contradicts what you’ve shared - I would say it’s better not to starve, yes, but it can also go too far in the other direction, with feeding too many “empty” calories; this seems to happen more often in parks and tourist spots.
Here’s the study I read, which talks about angel wing NOT being present until the swans (or cygnets) being studied were 10 weeks old. At 8 weeks (I think it was 8 weeks), they had normal wing joints. So it could be that some swans are more sensitive to any feed that isn’t natural? I don’t know about that part, as I’m not an ornithologist.
Almost every link I could find says it’s inappropriate diet, so I’d legitimately like to hear what the Swan Marker thinks causes angel wing, and his or her opinions on the algae bloom from bread? I’m not being a jerk; I’d actually like to know because you’re absolutely right; I’m sure he or she knows much more than I do, and maybe I’m just missing something here. But it seems like saying it’s not bread is a bit disingenuous; it’s feeding cygnets too many calories, and bread contains excess calories for a swan (except, as stated, maybe a rural adult swan in winter). Obviously, based on the papers, there are scientists much smarter than me trying to work this out. If you have a starving swan, and all you have is a bit of bread, feed them. If they are only adult swans and it’s winter, feed them bread, though still preferably not white bread. But IF you have the choice, other options might be better.
Paper showing normal wing joints then abnormalities start in some swans:
https://www.sciencedirect.com/science/article/pii/S0032579122006836#bib0027
Paper talking about angel wing on Clipperton Island:
https://www.tandfonline.com/doi/full/10.1676/11-208.1
And an ornithological group sharing a long article about angel wing and its causes:
https://ducksofprovidence.com/angel-wing-in-ducks/