I have four zebra finches, two boys and two girls, but only one female ever lays eggs. The finch will usually lay four eggs and then sit but some of the eggs always end up broken at the bottom of the cage and the ones that dont get broken always have a tiny hole in them.She will sit on the remaining eggs but obviously nothing is growing inside if they have a hole or crack. It shouldn't be a calcium issue because we I put calcium supplements and calcium chewy treats in their food. Could it be because there is more than one couple in one cage? Or is it something else?