I have heard that you can save egg shells and use them when the birds start their families. It helps harden the shells of the newborns. My question is, when do I mix the shells with the food? I live in Indiana if that helps. - Thank you
gizzard. To aid in the grinding, birds swallow small, hard materials such as sand, small pebbles or ground eggshells. Egg shells have the added benefit of being a good source of calcium, something birds need during egg laying (spring to late summer).
If you decide to provide eggshells, be sure to sterilize them first. You can put them on a plate or paper towel in the microwave on high for about 1.5 to 3 minutes (for a dozen, go 3-4 minutes), boil them for 10 minutes, or heat them in an oven (30 minutes at 250 degrees). Let the eggshells cool; then crush them into pieces about the size of sunflower seeds. Offer the eggshells in a tray feeder or mixed in with your bird food.
You can read more in the article: Creative way to recycle eggshells http://lansingwbu.blogspot.com/2012/04/creative-way-to-recycle-eggshells.html