It's one thing, it's the stomach, the bird's stomach is divided into myogastric and glandular stomach, the glandular stomach is smaller and secretes gastric juice, the myogastric stomach is larger and thicker and is responsible for storing and grinding food! The gizzard is the muscular stomach! The gizzard is also the stomach

Chicken gizzard, duck gizzard is the avian crop, is to help the digestive, birds do not have teeth, will swallow small stones, is stored there.