And you have to have the stored calcium to draw on.
Having raised chickens I know that a low calcium diet does result in egg with thin shells and hens eating their own eggs to get back the minerals expended in the laying.
Hens eat broken eggs, to be sure. And I had a Buff Orpington break her legs in a high jump. But hens are an exception. They lay nearly every day. Birds of prey will lay two to four eggs a year. Wild birds were destroying their eggs in the process of moving their feet around them and turning them as they incubated.