Birds are “masters of disguise” when it comes to hiding early signs of illness. Therefore, exterior indicators of health status are very helpful and important. Bird droppings are one of those critical exterior indicators, in conjunction with clinical signs such as fluffed feathers, energy level, and loss of appetite, weight loss, and so forth.
Droppings can be an important window into the health status of your bird.
This page deals with anything coming out through backdoor.