I would not feed layer to a flock consisting of drakes or other male fowl. The excess calcium is dangerous for them and can cause kidney damage/failure. This is why I suggested against treating the whole flock with even more calcium.
If you offer it free choice, the girls will eat it and the boys will leave it alone since they don't "want it".
Since they are on layer, I am more inclined to think that you have too many drakes and they are gang raping the hen, causing stress and possibly breaking her egg inside her during the struggle.
Let me be sure I have the numbers right. 4 drakes and 8 ducks? I would make a place for the boys to be separated for a little while so the girls can get their wits about themselves.
I'm also confused, you've found three of these eggs in one day? And the one that you witnessed coming out was already empty when she laid it?
If I don't feed the whole flock layer, what would I feed the male fowl? And how would I make sure they're each eating what they're supposed to be eating? Usually, we put the food out in feeders and let them have access to the food at all times. Would doing feeding times help with this? This could be very difficult with my husband and my busy work schedule during the week.
We have 4 drakes and 12 ducks (16 total).
Here's what happened: We usually don't let our ducks free range unless we can watch them because we are on the corner of two busy roads and we would hate to have them get hit. The other day, I let them out while I was working in the garden and they were all busy foraging and having a great time. However, off to the side, one of our female Pekins was lying in the grass, panting (like they usually do when they're hot). Her tail kept moving up and down and I thought maybe she was laying an egg. All of a sudden, one of the drakes came over and mounted her. I ran over to make him get off since it seemed like she was in a little bit of pain laying the egg. Once they both ran off, I found the empty egg shell on the ground where she was sitting.
The ducks ran over to the side a little more and I noticed that one of my Khakis was playing with another empty egg shell in a different spot in the yard. I grabbed it from him. So, that was two in one day...and they both happened around the same time. The other egg I found in their coop a different day, but it was a soft egg membrane with nothing inside of it.
And Amiga, I wish our ducks liked us as much as yours seem to like you. Our ducks don't want us near them at all. We had one runner that my aunt rescued from the canal when the duck was a baby (she came running over to my aunt; someone had dropped her off in the cold and a cat got her siblings so she was terrified and alone) and that little duck loved me to death when she was younger. She would sit on my lap and loved to cuddle. I was worried that she would be lonely without the company of other ducks, especially since I took her over one day to let her look at the others and set her down so she could follow me and she started peeping and trying to get to the other ducks. I thought she'd always like me, but once we put her in with the others, she won't come near me anymore. I hate it. This little lucky duck's name is Friday since we rescued her on Good Friday. I wish she still liked me, but she's taken hints from the other ducks. How do you make yours like you? Do you just devote a lot of time to them? Or is it because you let them free range and they're happier than mine are? It also makes it really hard to check them for things like bumble foot or prolapse if we can't get near them.