Author: Dr. Thomas Caceci
Pen-raised birds on commercial feed generally don't require that grit
be added to the diet, because the feed is formulated carefully to
break apart easily and so grit is unnecessary. Fruit eating
psittacines (parrots and macaws) also eat a very soft diet and so
they don't need grit, either. But many caged birds, including the
psittacines, do benefit from the presence of grit, and it's often
recommended. Oyster shells are frequently used, not only as a source of
grit for mastication, but as a calcium supplement. Birds have very
high levels of circulating calcium and a much higher metabolic demand
for it than mammals do.