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Who are you calling a dummy?

If you have been keeping up with Zoo Atlanta’s social media, or have had the pleasure of visiting us recently, you likely have seen that the Bird Department has experienced the baby boom typical of breeding season. Well, I am going to give you some insider information about one of the more useful tools in any Bird Keeper’s arsenal: the dummy egg.

In its simplest form, a dummy egg is a replica used to serve as a placeholder for the real things. The motive for using a dummy egg varies. Sometimes, it is a question of safety for the egg, but more often it is used whenever we do not want the birds to breed – the result of a management recommendation, genetic relativity, or we know that the pair in question are terrible parents. With the case of the latter, allowing a female to sit on dummy eggs discourages future laying and reduces the overproduction of eggs, which can be taxing on her due to the potential of causing calcium deficiencies or increasing the chance of becoming egg-bound.

Some species do not seem to mind what they sit on. For example, our flamingos will brood a clay egg sculpted by the Bird Team, while our tawny frogmouths will accept a ping-pong ball as a substitute. These are likely the type of parent most of your species who practice “brood parasitism,” such as cuckoos and cowbirds, hope to find. Brood parasitism, or the process in which eggs are laid in the nests of other birds, causes the eggs to be hatched and the young reared by the host, often at the cost of the hosts’ own young. So, being able to discern which eggs belong to your species and which don’t helps to increase the chance of survival for your young should your nest be targeted by a nest pirate. For some species, noticing the difference between eggs is as intricate as one female noticing which eggs she laid versus even the one laid by her neighbor – a specific example being the common murre, which nests  in densely packed colonies. The colors and patterns found on bird eggs are just as diverse as the parents themselves. Rather than painting these intricate patterns, we will create dummy eggs from old eggs, that is, eggs that were infertile from previous clutches.

The process of creating a dummy egg can be quite tricky, often taking several failed attempts before you are able to be successful. Eggs are designed to be sturdy enough to protect the developing chick inside but able to be chipped away for the chick to hatch. So, in other words, they are delicate. Frequently used in metaphors to demonstrate that something requires great care and consideration to not break it. Too much force at the wrong place or at the wrong time can easily lead to a broken or cracked eggshell, ruining the chance of turning the egg into a dummy. That is why, when first learning the skill, keepers are always encouraged to practice with chicken eggs purchased from the store.

The tools required for dummying an egg include a cup of water, an empty cup, a needle between 16 and 20-gauge, plaster, and lots of paper towels because it can be a messy process.

First, keepers will create a small hole on one end of the egg, typically choosing the one that has the air cell, the cell is found at the “fat” or most rounded side of the egg. (Next time you crack an egg, peek at the inside of the shell and the air cell will be that “squishy” part at one end). We want the hole to be small to have the least amount of effect on the pattern or coloration of the egg, but large enough to enable the dummying process. Once we’ve created our hole, we then will drain out all of its contents, often times using the needle to spray water into the egg until it is running clear. After allowing the egg to dry out overnight, we then add a plaster and water mixture, cautiously filling the egg. If you fill the egg too much initially, the plaster can expand and breaks the egg. Conversely, if you create an air bubble while filling it, you’ve also created a weak point where the egg may break as well. Once the egg is entirely filled, all that remains is to sand down any excess plaster at the hole.

And that’s it! The dummy egg is now ready to be deployed!

Cynthia B.
Keeper II, Birds

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