Birds need calcium to form eggshells and to feed their nestlings. Recent scientific investigations have shown that under certain conditions, birds cannot find sufficient sources of natural calcium.

There is a theory that acid rain may play a role in the scarcity of available calcium for the birds. In 1997 the Cornell Lab of Ornithology started the Calcium Project. Its purpose was to compare different species and geographic regions in the frequency that birds take artificial calcium. The results showed that all bird species took eggshells on both the ground and from platform feeders. Their conclusion was that people should provide crushed eggshells on both the ground and on platform feeders especially during the spring and summer when it is needed the most.

Eggshells are probably the cheapest feed you will ever feed the birds. Instead of tossing an empty eggshell rinse it out removing the inner membrane. The next time you use the oven place the eggshells on a tray and in the turned-off oven and let them sit. Or bake them for half an hour at 250 degrees. Crush the eggshells and add to the platform feeder or scatter on the ground.