It's happened to me a few times. I think they just step on one occasionally, in their clumsiness, and break it. I've found them half eaten, too. Evidently I've never gotten a true egg eater. I've read that if you do, there's really no way to break them.
But there is one thing: rollaway nest boxes. And one more you didn't mention, darkening the nest as with a cloth curtain -- if you can still get them to use the nest box. Evidently, what they can't see, they won't eat. Just what I've read on here.
But there is one thing: rollaway nest boxes. And one more you didn't mention, darkening the nest as with a cloth curtain -- if you can still get them to use the nest box. Evidently, what they can't see, they won't eat. Just what I've read on here.