Those bastids. Mine are doing the same thing. I've been overloading the nest boxes with storebought eggs (about 6-10 eggs per box) and it's keeping them busy enough that I think the issue has cut way back. I'm able to collect 6-7 eggs a day (from my 17 pullets). I don't think I could take away the storebought eggs without them eating their own yet. It's been about a week of this.
I have curtains on my nest boxes. Not sure if it makes a difference, but I've never had anyone eat an egg unless there was a broken one outside the boxes (laid from roost and broke on the floor)
Mine learned the bad habit the same way. Someone decided to leave an egg on the roost. My rooster broken it when he jumped down, and they all decided it was worth eating. Then they continued doing it when they would find other eggs in the coop/boxes. Doesn't help that I have a couple small barred rocks who still lay eggs on the floor of the coop occasionally. Just adds to the confusion.
I make my flock a dust bath in the winter. I use a black plastic trough (about 20x30 inches and 8" high) and use "play sand" (40# bag at HD) with a couple handfuls of fine wood ash mixed in. I put it in the corner of the coop. They really love it and use it a lot. Even when they are not taking dust baths they like to sit in it in a group.
I made a suet block earlier in the winter and put it in the run. The two white leghorns (other, darker girls don't show) got grease all over themselves and then covered it with dirt/dust. They are just nasty looking. Dust bathing has not helped. They are getting seriously soap & water BATHED when we have real hot weather. Until then, I'm just embarrassed.
