Gastrointestinal physiology and nutrition in wild birds

The avian digestive system clearly demonstrates evolutionary adaptations which reduce body mass to improve efficiency of flying.Teeth and heavy jaw muscles and bones seen in mammals and reptiles have been replaced by much lighter beak, jaw bones and jaw muscles.Because birds to not chew their food, the oesophagus is large in diameter to accomodate large items.The heavy muscular stomach (gizzard) takes over the function of teeth in mechanical digestion of ingesta.The main mass of birds, the breast muscles and viscera are 'suspended' under the wings for flying efficiency.The tongue and beak are used for food manipulation and exhibit many interesting adaptations in birds (McLelland, 1979).There is no soft palate in most birds and the hard palate connects with the nasal cavities via a median slit.Salivary glands are poorly developed in species that ingest aquatic food and well developed in those eating dry food.The glands of some species (e.g.house sparrow (Passer domesticus)) contain appreciable amounts of amylase (EC 3.2.1.l), but those of domestic