Have you ever wondered what happens to the shells left after bluebird hatchlings peck their way into the light of day?   You do not see them in the nest nor on the ground beneath a nest box.  Since you know they do not simply vanish into thin air, there must be a logical answer to this age-old mystery. Actually, one of two things can happen to the shells.  Most birds, including the eastern bluebird, carry the shells some distance from a nest and simply drop them.  This is why, as you walk about your yard, you sometimes stumble across wild bird eggshells in places where no nests are in sight.  Many bird experts suggest this behavior makes it more difficult for a predator to locate a nest full on young, helpless birds.  If the eggs were simply dropped out the entrance hole, a predator would have a much easier time finding a nearby nest. In the case of the bluebird, parents sometimes eat the shells.  Nobody knows why they do this.  It is thought that perhaps it is done to obtain the calcium found in the shells.