Calcium in Birds

This video is not geared toward pigeons but all avian species.

Very helpful video!
I've discovered first hand how easy it is to think if a bird has adequate grit and oyster shell it will be fine, but that may not be any way near enough.
There's good information on the various types of calcium supplements and the times when birds need them most.
I would only add a final note: if your bird has an adequate calcium and vitamin D3 supply and still shows symptoms of lack of calcium, he may not be able to absorb it and will need to see a vet.