Which is a Natural Calcium Rich Food for Birds ?

Most of the birds required calcium and minerals for their body. The only natural source for calcium is from the cuttle bone. The cuttle bone is a kind of sea creatures extra part. Its like a shell for a pearl. It have the digestable quality calcium which the birds need. If the calcium is high then it will be digest for birds. So keep this cuttle bone in every birds cage. It will bite whenever it feels bore. It should not be a main food source. Its just a supplement for birds. Most of the birds which is inside the cage wont lay eggs. Since it doest have the adecute calcium required to build the shell. So to be very effective in breeding we should keep the cuttle bon in every birds cage.