Grit is used by birds to aid in the digestion of whole, intact seeds. Birds' digestive enzymes work well in digesting the inner portion of seeds, but have difficulty with their fibrous coating.

Grit is a fine, gravelly substance given to pet birds as a dietary supplement. When a bird eats grit, it makes its way to the gizzard where it helps to grind up food (seeds) into smaller particles that are easy to digest. (see link below for complete information)

Birds can't chew -- they need the grit and stones in their stomachs to break down the food to digestible states.