The manure as an indicator

To understand possible causes of changes in the appearance of bird droppings, some knowledge of the anatomy of a bird's digestive and urinary tract is indispensable. Most bird species have a crop — a sac-like dilation of the esophagus that serves as a food store. The feed is moistened in the crop, but no digestion takes place. The bird stomach consists of two parts: the glandular stomach and the gizzard stomach. The food first reaches the glandular stomach, where digestive juices such as stomach acid and pepsin are added.