Final answer:
The partially digested food in a bird moves to the second chamber called the gizzard, where it is ground up for digestion.
Step-by-step explanation:
The partially digested food in a bird moves from the crop to the first stomach chamber named the proventriculus, where digestive juices continue to chemically break down the food. From the proventriculus, the food moves to the second chamber, known as the gizzard. The gizzard is a muscular stomach that grinds the food with the help of swallowed stones or grit, aiding in the bird's digestion process due to their lack of teeth. Waste products and undigested material are eventually excreted through an opening called the cloaca.