The digestive system of birds includes an esophagus, crop, stomach with two regions (proventriculus and ventriculus), intestine, and cloaca. The crop acts as a storage organ that allows birds to quickly ingest large amounts of food and digest it later. In pigeons, the crop produces "pigeon's milk" which young pigeons feed on. The stomach contains the proventriculus, which secretes gastric juices, and the ventriculus or gizzard, which has muscular walls to crush hard materials like seeds. The intestine absorbs nutrients with help from the pancreas and liver. The cloaca is the last part and acts as a common opening for waste elimination and the reproductive system