They do this because they are trying to make a hollow in the bottom of the egg box.My hens are just starting to lay(i have 5) and they keep kicking all of the bedding out of the egg boxes. How do i prevent this. Because of this the first egg i found was broken in the box because there was absolutely no bedding.
This article explains a little about it.
@Pork Pie use of earth is ime better than any of the loose bedding. If you can keep the earth slightly damp even better.
While you're think about egg box problems it may be worth considering what makes an adequate box for just laying eggs isn't necessarily so good if you are planning on letting your hens sit and hatch in them.
https://www.backyardchickens.com/ar...e-make-a-sitting-hens-job-so-difficult.74389/