Chickens need calcium to make eggs with strong shells.
Chickens need grit in their craws to grind their food for digestion.
Chickens lay eggs with shells high in calcium.
Chicken egg shells can be crushed to provide grit for the craw.
So there it is: the ultimate recycle.
From the chicken to the table and back to the chicken.
The shells need a little processing. Giving "raw" shells to them can cause chickens to peck at fresh-laid eggs in the coop. That's not good. The reason they will do this is that with raw shells, there are bits of egg white still clinging to the shell and the chickens can develop a taste for it.
To avoid this problem, bake the shells at a low temperature for about 15 minutes. The baking will make the shells more brittle and will completely cook any remaining egg in the shell.
Once the shells have been baked they can be crushed easily into little pieces and fed to the hens.
They love it! I like it because the shells get used and my chickens are happy.
A win-win situation.