My 7 Rhode Islands have been doing great laying eggs until this morning. I have a small coop (4x4 pallet with 3 nesting boxes attached to the outside), yes I know it is small for that number, but when I opened it this morning I found this egg lying under the perch's. It is perfectly round, and smaller then the golf ball in the picture. What could have caused this? Is there something I can do to help prevent this from happening again?