Are you sure its the chickens? The reason I ask is because, in my experience, when my chickens have eaten an egg I usually only find some residue from the yolk. When I had a problem with mice, I would find empty shells that had been licked clean. Where do your chickens typically lay? Is it in a place where the eyes could get broken like from high up or on the floor? Maybe your chicken has been laying soft shell eggs and that's why they're eating them? I've heard you can blow out an egg and fill it with mustard to discourage egg eating, but my chooks have never had any issue eating something that had mustard on it. IMO- the only way to know 100%if that the birds can't get to their eggs is to build some roll away nestboxes. If they were mine I would spend some time at the coop when you have a chance to see if you can catch whoever is doing it. Good luck....