Hi,
When the hen discards the eggs like that, then she knows they were not any good, or that the chicks had died in the shell. The eggs hatch 18-23 days after she starts to sit, so by the time she threw them out, the last egg was on the last due date and the others were overdue. There is no need to incubate them – she knew they were not going to hatch. Even if they were not past the due date, they can’t keep developing when there is a hole in the egg. I know it is upsetting, but the best thing to do now is to remove the nest box and make the pair rest for 6 months before letting them nest again. The hen needs this rest to recover from the stress on her body from laying eggs. As for why it happened, she may not have sat on the eggs around the clock and let them get too cold at some point, or the chicks may not have been able to hatch. If the environment is too dry, the shell gets too hard and they can’t hatch. The hen will normally take a bath and carry water into the nest on her feathers. If this was her first clutch, she didn’t know exactly what to do, so maybe she will do better next time.
Thank you for asking Lafeber,
Brenda