Eggshells

Preparing Eggshells for Martins

Many landlords offer their martins eggshells or oystershell as a source of grit and calcium. Crushed oystershell can be purchased pretty cheaply - usually from feed stores, in a 50# bag - but it can be stored for several years of use. Our martins eat oystershell readily, and also feed it to their nestlings. The martins' diet of insects offers them plenty of protein, but no calcium - so the supplemental eggshell or oystershell is a good extra to supply. The martins will collect pieces of shell on their own from nearby lakes, etc - we have found pieces of clam shell in the nests, also fish bones, mussels, and snail shells.

To give the martins chicken eggshells, you can save eggshells from your kitchen (keep them frozen or refrigerated if you are not going to process them immediately), or ask a local restaurant to save you a bucket of eggshells from their breakfast preparations. The eggshells should be rinsed in cold water to remove the gooey albumin that lines the shells, but it is not necessary to remove the papery membrane that lines the shells. To kill bacteria such as salmonella, toast the eggshells in a 200 degree oven for about 10 minutes - spread them out on cookie sheets to make sure all surfaces are completely dry. Then crush the shells to roughly 1/4 inch size pieces and store in a ventilated container. Since microwave wattage varies, we cannot give you exact times or heat settings - if you use a microwave, just be sure all surfaces of the shells are completely dry, so no bacteria can survive. Eggshells can also be processed by boiling them for about two minutes. Using the shells from hardboiled eggs (including dyed eggs) is not recommended, as it's difficult to remove the all bits of cooked egg from the shells, and there is a chance it will spoil and could sicken the martins.

You can spread the shells on the ground below the martin housing, or place them in an elevated platform feeder. Replenish as needed - you may need to stir them up after it rains, too. Other birds may also come for the eggshells, including barn swallows. You can put eggshells out in the winter, too - according to a study done by Cornell Lab of Ornithology, about 60 species of birds will consume them for the grit and calcium they contain.