Well, my hens have been laying for a little over 3 months. Their eggshells have been really super hard all along. I realized that their layer feed contains extra calcium, so wonder if I even need to provide oyster shell? Their bin ran out so I waited a few days before re-filling (found a brand new bag in storage) so I put it out for them. They attacked it like it was mealworms! I guess they need it?! Figured it was something that they would go for on an as-needed basis, so it looks like they really do need it. Right? They also free range for just a bit each day.