Candidiasis, also known as thrush, moniliasis, sour crop and crop mycosis, is most commonly due to an overgrowth of the yeast Candida albicans, which can be part of the normal intestinal flora and is frequently isolated from droppings of normal birds. It is primarily a disease of the upper gastrointestinal tract (oropharynx, oesophagus and crop), but can be found lower in the tract on occasion.