off the top of my head:
Vit A deficiency (very common)
candidiasis (candida albicans)
aspergillosis/fungus
...all of the above can be in combination with other conditions (any could be primary cause of death or secondary to primary cause of death)
Ja it is difficult to narrow down an illness by the symptoms (same symptoms will present with many conditions) it is also equally true with superficial lesions from a necropsy...you did not give any symptoms the bird had before death so I would not even hazard a guess. Also, as you did not have...