Now that my season is over I like to herald in the fall by placing my egg shell collection container on my kitchen counter. True, it is not the most decorative touch but it reminds me to continue to save egg shells and build up my stores for the next season. In reality it is nothing more than an old Folgers coffee container with holes poked in the top to allow air circulation and my husband always seems to be trying to hide it away, under the sink. But one could decorate it nice if you were concerned over the aesthetics of it all. What’s the big deal? Plenty, if you want the most from your purple martins nesting efforts.
Some folks get it all done and over with by going to a local diner or restaurant and just asking the cook/chef/manager for their egg shells from breakfast service. It sure would make my counter look nicer without the old Folgers can. Of course the best way (as recommended by the Purple Martin Conservation Association) is to actually purchase a bag of Oyster Shell. But however you do it, supplemental Calcium has been a staple of the bird business for as long as folks have been breeding birds.
The actual preparation of egg shells is pretty easy. And “yes”, you do have to prepare the egg shells. It is quite easy and just following these instructions on “Preparing Egg Shells” at our parent site, gives an easy recipe, of sorts.
As mentioned earlier, the PMCA actually recommends using Oyster Shell which is sold as a chicken supplement. It is easily found at any feed store, grain store or the like. Not all are created equal, however. Look for the “pullet sized” which are bigger pieces meant for supplementing chickens as some calcium supplements are in a powder form and way to fine for supplemental feeding. If it is too fine, it will just blow off your elevated feeder. If the oyster shells in the bag you purchase are too fine, just make note and don’t buy that brand again. The only thing the dust version of the Oyster Shell is good for is for your garden, in some cases, to ‘sweeten’ the soil. And if you see “Coral” anywhere on the ingredients, beware- you may end up with a bag of coral dust.
If you are wondering what the big deal is, you can read more here: EFFECTS OF SUPPLEMENTAL CALCIUM ON THE GROWTH RATE OF AN INSECTIVOROUS BIRD: THE PURPLE MARTIN (Progne subis) By Ray Poulin
The PMCA also has an article in their publication The Purple Martin Update Vol. 15 (2) on page 20 I believe that is an interesting read. Contact the PMCA for a back issue of that.
To paraphrase all and take from my own experiences with domestic birds; by providing supplemental calcium you will help your female purple martins in how many eggs are actually laid and the number of birds that actually hatch. Also the nestlings with supplemental calcium have longer feathers at the same age and better growth rates overall. Though the PMCA states that Oyster Shell is much better absorbed than eggshell, if you can’t get the Oyster Shell, Egg Shells are better than nothing.