I am feeding Exact baby bird formula. Not calcium, grit or anything else needs to be added.The adult pigeons consume little bits of grit and oyster shell that they feed to their babies with the grain they consume. The babies need the calcium in particular. They're growing a lot of bone and feather quickly. You could get some tablets of tablets of calcium such as Tums and break them into small pieces and give a bit every day. The baby also needs a bit of Vitamin D3 through exposure to the sun or from feed sources to metabolize the calcium.