My first girl to lay is a Buff Orpington. She has been laying for about a month. At first everything went as I had hoped. She surprised me that she lays almost everyday. Lately she has been laying rubber eggs at night. This happens about 3-5 times a week. When I go out to check on the girls in the morning, there is a rubber egg along with the droppings. She still lays regular eggs during the day. What is causing this? What can I do to stop it. She has crushed eggs shells available, and is on Purina Layena. Any ideas? All of my girls free-range most of the day and than are locked in the coop at night.