I found a little less than half of an eaten egg in a nest box today. The first time this has happened for the four months we've had the chickens. I've been feeding them layer pellets with a daily scratch (sometimes twice daily) supplement along with grit. I also put out a "flock block" that has oyster shell mixed in. I looked around the coop and yard and checked the chickens for evidence of who ate the egg (was looking for maybe some yolk mashed in the feathers) but didn't see anything. How can I tell if one of the chickens ate the egg or if it was eaten by something else, e.g. a mouse? I've seen a mouse run out of the chicken coop one morning about a week ago and haven't seen it again since. Any suggestions? I'd really like to not starting losing all our eggs!