Our hens have just been laying for a few weeks now and every now and then, we find an egg without a shell under the roosts. Today, I found one in a nest box. They get Certified Organic feed and free range daily. The shells of all of the eggs are very solid so I am sure they are getting enough calcium. (We also have oyster shell available at all times.

Is this just because some of the birds still have immature systems? I can't tell if it is the same hen with the problem or several.