Not a bird expert by any means, but could it be a naturally occuring mutation as is found in some breeds of dogs ? Are you mixing the breeding stock ? Also, any fumes from any substance can irritate mucus membrances, ie, ammonia attaches directly to mucus membranes. Eye and throat irritation at even low levels, blindness and suffocation due to tracheal swelling at higher levels. Same with some paint fumes I imagine. Anyway, not a know it all, I was just thinking on the subject when I read the post.
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