It's my understanding that you don't have to bake them, but the less they resemble the original egg shell the better. Otherwise the hens may associate the shells with something tasty and then you end up with a bunch of egg eaters.
Thanks for all your replies! I am so relieved to not have to bake the shells first. I have just been throwing them in the food processor with all kind of other stuff and then giving them to the hens. I love this website!
I pop them in the microwave for a few minutes just to make sure and kill off any bacteria. Dont want to take the chance of spreading bacteria from one bird to another. Its good bio security in my opinion.
I like to bake mine for the same reason as coffeelady3 said. The less they resemble or smell like eggs the less likely someone is to end up with egg eating chickens. I figure it's worth the extra effort... just to err on the side of caution.
Meh - I don't bother. Just leave them on the counter until they've dried out, crush them, then add to the crumbles/pellets.
Chickens don't have deductive reasoning. They can't look at a piece of an egg shell and logically come to the conclusion that it's related to the thing they push out daily, then make the leap to the fact that their eggs are tasty. We can make those leaps, but chickens cannot.