Digestion a thin-walled expanded portion of the alimentary tract used for the storage of food prior to digestion. In some birds it is an expanded, muscular pouch near the gullet or throat. In adult doves and pigeons, the crop can produce crop milk to feed newly hatched birds. Certain insects may have a crop or enlarged esophagus. Herbivores have evolved cecums (or an abomasum in the case of ruminants). Ruminants have a fore-stomach with four chambers. These are the rumen, reticulum, omasum, and abomasum. In the first two chambers, the rumen and the reticulum, the food is mixed with saliva and
Human uses of birds whereas an antelope can yield as much as 31,000 kcal/hour, and wild rye around 1,000 kcal/hour. Birds have been domesticated and bred as poultry for use as food for at least four thousand years. The most important species is the chicken. It appears to have been domesticated by 5000 BC in northeastern China, likely for cockfighting, and only later used for food. In ancient Egypt, poultry including ducks, geese, and pigeons were captured in nets and then bred in captivity. Chicken now provides some 20% of the animal protein eaten by the world's human population in the form of meat