The digestive system of the birds have some unique aspects in that it stores food temporarily in the crop, and masticates it in the gizzard rather than in the mouth like the other animals. The vertebrate gastrointestinal tract is a dynamic organ (Brugger, 1991). The digestive organs of birds consist of the epithelium derived from the endoderm (Romanoff, 1960). Birds have a digestive tract (GI tract) that is much shorter (to reduce weight for flight) and have a specially modified stomach for processing seeds and plant material. In pigeons, the crop lining changes dramatically when they are...