It begins with entry of food via the beak and ends with the exiting of refuse at the vent.
Food is broken down and absorbed for use along the way.
The avian beak or rostrum is composed of bone and an outer horney Keratin sheath or rhamphoteca . Keratin replacement continues throughout the life of the bird. In large parrots, the keration is worn down by digging, eating and chewing on hard objects and is completely replaced in 6 months on the upper bill and in 2 - 3 months on the lower bill. The upper beak is the maxillary rostrum and the lower beak is mandibular rostrum. The cutting edges of the beak are tomia , which take the place of teeth.