Final answer:
The esophageal diverticulum in birds used to store food is called the 'crop,' which leads to a two-chambered stomach comprising the proventriculus and the gizzard for digestion.
Step-by-step explanation:
In many birds, a diverticulum of the esophagus, the crop, can be used to store large quantities of food. This sac-like structure not only functions as a storage space but also moistens the food. Birds then typically move food from the crop to the proventriculus, where it encounters digestive juices. Subsequently, the food passes to the gizzard, a strong muscular organ that, with the help of ingested stones or grit, mechanically grinds the food. This adaptation is particularly crucial for birds as they have high metabolic rates to sustain flight and lack teeth to chew their food thoroughly before ingestion.