Seeds taken in by pigeon pass from the esophagus into the buccal cavity, which consists of a hard and a soft part, and where saliva is added. Saliva contains enzymes that begin digestion by breaking down carbohydrates. Next, the grain moves into the crop, a widening of the esophagus, where it is softened in water the bird has drunk. Food is slowly fed in small quantities into the proventriculus, or glandular stomach, which releases the enzyme pepsin and hydrochloric acid acts as an antiseptic defense against any fungal or bacterial organisms taken up with the food, and dissolves the calcium salts in feed
The swollen grain,in almost its original form, passes from the proventriculus into the ventriculus gizzard (muscular stomach).There it is ground by the heavy muscles lining the gizzard against the grit (tiny sharp gravel), turning the soften grain into a thin porridge that is then dumped into the small intestine.The small intestine consists of the duodenum, jejunum and ileum. The duodenum is loop-shaped and contains pancreas,which dumps its secretions into the duodenum.Digestive enzymes further break down the proteins into amino acids,carbohydrates into various sugars, and white bile released into the jejunum by the liver, helps convert fats into fatty acids and glycerol.Pigeons are non-gallinaceous, ie they do not have a gallbladder that store bile.
The small intestine is richly supplied with blood vessels amplifying the surface area through which the totally fluid nutrients can be absorbed into the bloodstream. The indigestible remains of the food are passed into the large intestine and excreted via cloaca, a cup-like , shallow chamber just inside the vent, into which the intestinal genital and urinary canals all open