Eggshell Feeder

This is the Purple Martin Conservation Association's unique new Purple Martin Eggshell Tray. It is a practical and attractive device for augmenting your martins' calcium and grit needs. Martins not only will eat the shells themselves, but they will also feed them to their nestlings. Research has shown that martins without a readily-available calcium source often have nestlings that suffer fatal calcium deficiencies.

How to mount your eggshell tray:

You will need to provide a 5' long 2" x 2" post for mounting the tray. The post can be cedar, pressure-treated lumber, cypress, or other long-lasting types of wood. Attach the tray to the post using the screws provided. Tighten securely. This tray is are made of select Western Red Cedar, one of the most weather-resistant of all woods. No treatment of the product is necessary, however, if you preserve it with hot linseed oil, or clear polyurethane, it will enrich the wood's natural color and prolong its life. Both products are available at all hardware stores and can be applied with a paint brush.

Where to place your eggshell tray:

The best location for the tray is 10-15 feet away from the base of your martin pole. This will place it at about a 45-degree glide path from the top of the martin house. Using a post-hole digger, dig a 2-foot deep hole in the ground and place the post into it vertically. Fill in around it with dirt. Pack the dirt tightly. Cementing the post is not necessary.

When to start offering eggshells to your martins:

Martins should be offered eggshells as soon as the very first one returns in late winter/early spring and they should continue to be offered it until the very last one leaves the colony site in late summer. Other common yard birds may also partake of the offerings. Add additional eggshell to the tray as needed. After each rain, walk by and hand stir the eggshells to speed their drying. At the peak of eggshell usage, you may have to add a handful of shell every day or two, especially if you have 50 or more breeding pairs of martins.

Sources of eggshell:

You can save eggshells from kitchen use all year long. White eggs are better than brown because martins seem to prefer white-colored particles for their grit. (Note: we find that the shells from hard-boiled eggs are not satisfactory because they often don't separate from their contents "cleanly." And obviously, the color-dyed shells of "Easter Eggs" are also not recommended.) By far the best source of eggshell is under the golden arches of your local McDonald's restaurant. In one morning, they use many hundreds of eggs whose shells they just toss into a plastic garbage bag and throw away. Talk to the store manager. Most will agree to save a bagful for you once in a while, or allow you to scavenge through their dumpster for the bag in late morning. You can also purchase crushed oystershell at many feed or farm supply stores. Like eggshell, oystershell supplies calcium and grit.

How to prepare your eggshells:

Use only relatively clean eggshells. It is all right if the eggs have a little liquid (or dried) yolk and eggwhite on them, but they should not have large quantities of egg or other food stuffs stuck to them, especially if fished out of the garbage. Soak the shells in a sink full of cold water. Then "toast" them in a 200 degree oven, for about 10 minutes (this kills bacteria, such as Salmonella, that could be harmful to the martins). When thoroughly dry, the eggshells will crumble easily into tiny pieces. Place several handfuls into a bucket, then smash them with the head of a hammer. This is the quickest way to pulverize the shells. When this batch has been smashed with the hammer, add more eggshell to the bucket and repeat. When all of the eggshell has been smashed with the hammer, further pulverize the shell fragments by hand. This is most easily done by rubbing handfuls of shell particles between your hands. When the shell fragments are the size of sunflower seeds or smaller, they are perfectly pulverized. Store in a container with a ventilated lid. A 5-gallon, plastic bucket with holes punched in its lid is best.

Other Uses for your Eggshell Tray:

Live mealworms or crickets can be placed in this eggshell feeder to train martins to take them during bad weather, and you can also place dropped insect prey from under the martin housing. During the off season, the eggshell tray can be used as a platform feeder for seed-eating birds. Just mount the unit in the ground near your other feeders, then fill it with birdseed.