Over-consumption of fresh fruits or vegetables may cause diarrhea in birds, as may stress. Diarrhea that persists, however, may be a symptom of some other illness, including GI tract problems, liver disease or parasitic gastroenteritis. The feces will appear watery and unformed. It's very important to make sure the bird experiencing diarrhea does not become dehydrated. If your bird's diarrhea persists for more than 24 hours, consult your avian veterinarian.