Hagen's Cockatiel Gravel is a natural aid to digestion and is properly sized for cockatiels and similarly sized caged birds. Cockatiel Gravel contains charcoal and oyster shells to combat common hyperactivity in the stomach. Birds that eat seeds whole need gravel in their gizzard to crush and grind the outer layer of seed to get to the inner nutritious part. Remember, birds don't have teeth. Cockatiel Gravel is specifically formulated and properly sized for cockatiels and other medium-sized birds.