I have a couple hens that are soft shell laying every other day just about. I have oyster shell in a container in their yard for them to eat as they want, but they dont seem to ever be eating it. I also give them egg shells and they love those. I threw some oyster shell in the yard with mealworms yesterday evening and they seemed to eat a pebble or two. Do they just know to eat it? What can I do to attract them to it more?