Poultry refers to domesticated birds raised for meat or eggs. Common types of poultry include chickens, turkeys, ducks and geese. Poultry have feathers covering their skin instead of fur or hair. Their digestive systems differ from mammals in that they lack teeth and have a crop and gizzard to help break down food. Poultry also have lighter skeletons with a breastbone (keel) to aid flight. Their reproductive systems are also distinct, with females determining offspring sex through their ZW chromosomes.