instinct to clean up anything that would attract predators. an infertile egg starts to go bad when under a broody and smell.I've had plenty of egg eaters, but none that specifically target infertile eggs. How would they know? There isn't any development, and they're not brooding on them, so it doesn't make sense to ditch them
usually, egg eaters just want the extra proteins or calcium and then it becomes a habit. the egg eater i had stopped when i cooked up eggs and fed them back to the flock. when i started feeding higher proteins feed it wasn't a problem. i always have oyster shells on the side, but some like the egg shells too