I have six chickens, four are pretty steady layers and good quality eggs. I expected the last two to begin laying in the next few weeks and this morning I discovered two eggs in the nest box that were shell-less. I am pretty sure it is my last two hens starting to lay, cause I haven't had this problem with the other four. They are spoiled chickens for the most part, I feed them organic egg laying food, give them plenty of oyster shells and grit, plenty of scratch and treat them with kale, squash, etc, and I even treat them with yogurt now and again. The temperatures here in Oregon are beginning to drop (30's) and the only thing I have done differently is to shut them in at night, closing off their door so less draft. Could that have something to do with the shell-less eggs. I heard that stress can cause that as well.