We have five hens in a run together. The older two have been laying for a while now with no issues with their eggs. The younger three have all just started laying in the last week, but they have been in the run with the older hens for a couple of months. For the past two days when I've collected the eggs there have been one or two that have been pecked on the shell but the membrane has not broken. Any suggestions how I stop this behaviour to stop them progressing to egg eating?