What to give and not give your parrot can drive a person crazy. I have given him literally a dab of peanut butter off of my finger and he goes crazy for it. But not more than that, because I've read peanut butter can be toxic - or is that fresh peanuts in the shell..? I've given him sweet potatoes - which he likes, but I didn't know butter was allowed.
Yes it can drive you crazy! Understanding a "healthy" diet for parrots is sometimes like understanding the equations behind quantum mechanics lol. Real butter (not margarine) is a nice treat for birds, as is cheese and yogurt. I've never met a zon who didn't love dairy products.
I have given him a tiny piece of toast but then heard bread (i.e. yeast) is not good for them. I'm going loony and becoming an overprotective bird mother here. He loves almonds but refuses to crack walnuts in the shell unless I do it for him and then give him the walnut out of the shell. He likes Blueberries and sweet fruits. Tried spinach, kale and broccoli and string beans and he doesn't touch those.
Amazons don't have powerful enough beaks to crack walnuts. Half-crack it with a nutcracker and "help him out"
Bread in and of itself is not bad for birds, it's the 'modern' bread that should raise concern. Read the ingredient label on the bread. If theres stuff that really oughtn't be in bread (i.e. much more than flour, yeast, salt, sugar), I wouldn't give it to him personally. The bread you buy at the grocery store is full of all kinds of mold inhibitors, HFCS, preservatives, flavor enhancers, things that make it a uniform texture.... It can give US intestinal yeast if we eat too much, and it can do the same to your bird. "Normal" bread (homemade or sprouted grain/organic from the store) has a much more acceptable ingredient list that is fine in reasonable quantities for birds
I always say, some is better than none with fruits and veg. If he likes xyz fresh produce, then that's what you should offer until he opens his mind more. I also keep in mind, parrots do not eat spinach, kale or broccoli in the jungle, they eat fruit. The NATURAL sugars in fruit can make for some extra unpleasant (for us) hormonal stuff that time of year, but I'm not convinced fruit is bad for animals who live primarily off fruit in nature:20: Just watch too much citrus, as it is acidic, but fruit, IMO, is a healthy part of a parrots diet.
And just to make matters even more crazy, both of his avian vets don't think its the zinc anymore. So I am wondering - what the heck does he have??
The damage FROM the zinc as Kiwi mentioned, now that makes sense to me. Why wouldn't his vets bring that up though? Did I mention he has stress bars on his feathers from all he's been through? Do those ever go away?
Maybe they didn't think about it. Next time you speak to them, just bring it up in a "I was thinking, and wondered if this could possibly be the case" and just get their opinion. Truth is, your bird is EXTREMELY lucky. Many birds who get zinc poisoning don't make it to see what the long term effects are. It's worth bringing up, especially if it's more intermittent now.