Digestive System

Because pigeons have no teeth, swallowed grain is first softened rather than chewed: it passes through the toothless beak, buccal cavity (where a narrow horny tongue and numerous mucus glands help lubricate it), pharynx and oesophagus into the crop, a thin-walled, bilobed elastic sac that stores food and softens it further using mucus, buccal secretions and body warmth. From the crop, food moves into a two-part stomach - first the glandular proventriculus, whose mucous lining secretes gastric juice, and then the muscular gizzard (ventriculus), whose thick, tubular-gland-lined walls and swallowed grit (gastroliths) grind the food into fine particles. The resulting material passes into a U-shaped small intestine (duodenum and ileum), where pancreatic juice (via three ducts from the pancreas lying between the duodenum's limbs) and bile (via two ducts, since pigeons uniquely lack a gall bladder) complete digestion; villi lining the ileum absorb the nutrients. The short large intestine that follows is differentiated into a rectum, with a pair of small blind rectal caeca at the ileum-rectum junction, leading finally into a three-part cloaca - the coprodaeum (receiving the rectum), the urodaeum (receiving the urinogenital ducts) and the outer vestibule or proctodaeum, which …