The Skinny on Offering Eggshells to PMs

[Professor BirdBrain]

In another conference, Wilson imports a photo of his martin nest with two eggs. As an aside, just in case he does not know, I want to tell Wilson that he has a subadult pair and subadults typically have 3-5 eggs in the nest. When all the eggs are laid, Wilson, check the date of the next to last egg, called the penultimate egg and now count 15-17 days later.

(There will be a quiz on this next Thursday!)

These two days are when the eggs will potentially hatch. All eggs will hatch within a 36-hr time frame. Just some thoughts, Wilson.

Here is the skinny on eggshells:

Hard to believe that ordinary eggshells are so important to birds in their lives!

Eggshells are not food for the birds, but mineral supplements to their diets. Birds, in general, have a great need for calcium and other minerals, particularly when they are in egglaying mode. Many birds will seek out spent or broken eggshells only to ingest them for themselves or to bring to their young in the nest. In Nature, nothing is wasted!

Do provide crushed eggshells for your martins to ingest for grit and as calcium need. Females need crushed eggshells for calcium when they are laying eggs.

Both males and females ingest and need eggshells for grit to aid in their digestion. Since birds don't have teeth, they need gritty substances, even dirt and minute pebbles, to ingest, take into their gizzards, a very strong muscle that digests food in lieu of teeth, to help them digest the insects that they eat. While many insects are soft bodied, there are many insects that have tough exoskeletons with chitin and are more difficult to digest.

Young need their parents to bring them eggshells so that they may have strong bones in development.

By providing eggshells on an elevated platform, you are saving them from going to dangerous places, like streets for small minute grains or pebbles and getting hit by cars or being taken by predators such as cats.

By providing an elevated platform and away from the martins' houses, and closer to your house (within 20 feet), you provide yourself with a wonderful observation platform where you can watch, observe and enjoy the martins.

A very, very good reason to relocate your eggshell platform AWAY from the martin houses and/or gourdracks is to protect the females from harm. As we all know, males will mateguard their respective females against the actions of other mated males as well as the roving eyes of all the bachelor, superfluous males without a female. And, as we, again, know subadult males are not the best protectors. Remember! Subadult males (and subadult females) are teenagers breeding. And, as such, subadult males leave a lot to be desired in protecting their females from the advances of other males. Many of these encouters with males ends up in the injury of the female. Sometimes, the females die from such injuries. While a delicate subject here, we must know and realize that, many times, the females are gang jumped by roving males, hoping for a copulation. It is these particular instances where female martins get quite banged up.

It is best to relocate the eggshell platforms farther from the actual colony site. By doing so, the females are more protected and are away from the roving male eyes of the colony. The females are quietly able to get away and go to the platforms in hopeful peaceful conditions.

I, myself, have two platforms. One is 15 feet from the house (five feet off the deck) and the other is about 7 feet from another window. Both are 70 feet away from the colony site. Martins use these platforms everyday.

During the time when the nestlings are being reared inside their natal compartments, there is more activity on these platforms, particularly in early morning and early evening. In the evenings, it is like a social gathering of awkward walking martins, milling around like little penguins, socializing and ingesting eggshells. Many times, it is only young and old males. Sometimes, the platform resembles a singles bar for Purple Martins.

If you have not done it this season, do plan on it next season. The Orange PM StarFeeder is a good platform to use for this. With five points, martins can walk to the center from one of the points and not have confrontation with another martin.

Also by providing crushed eggshells for your birds, you will observe many other birds coming to the platform to take them for themselves or their young.

It would be nice to know of a source of clean, washed crushed eggshells if anyone knows one. Many landlords save them year-round or make arrangements with restaurants that use many dozens of eggshells to save them.

For instance, there are always the local fast food restaurants that offer daily breakfasts. They may laugh but most often, places like this will humor you and save you the morning's eggshells from their egg dishes.

I save each one of my eggshells throughout the year. Then I wash them and remove the membrane skin inside and nuke them for 2-3 minutes. You will know how long to microwave your eggshells. If you smell that familiar smell like your teeth are being drilled by the dentist, I would say, you have timed the microwave too long.

After microwaving the eggshells, I pulverize them to the size of the top of a pencil eraser. For myself, I use a food processor to do this.

A few years back, we received information from a Minnesota landlord telling us of a report from the University of MN Raptor programs that told of the possibility of eggshells cutting the gullets of birds as they ingested them. Reducing the size of eggshells will hopefully prevent this in martins.

It is very important to keep eggshells in a paper bag and not a plastic one. In a plastic bag, moist organic materials such as in eggs can foul the entire lot. Best to keep in a ventilated container to prevent ruination of your hard work in saving eggshells.

In addition to eggshells, PM stewards should also offer their martin colony shredded cuttle bones and bird mineral cakes, both of which are sold in stores that cater to exotic birds, like parrots. Cuttle bones are the skeleton of the cuttle fish and is a very soft bone and is easily shredded with a pen knife. On the other hand, a bird mineral cake (B & D brand name comes to mind) is a square of harder minerals. You can also shred this with a knife but it may need to be more coarsely pulverized.

You see, eggshells only offer calcium but cuttle bones and mineral cakes offer a variety of minerals, all of which martins can use as well as any caged exotic parrots.