Egg Candling:
How to See If Your Birds' Eggs Are Fertile

The Basics

A female bird's eggs cannot be fertile unless she has had sex with a male bird of the same species. For instance, a female lovebird must have sex with a male lovebird; a female African Grey must have sex with a male African Grey, etc. The male bird can be a different color; for instance, a pied cockatiel and a lutino cockatiel can make fertile eggs together. The female must have had sex with the male sometime in the week prior to laying her eggs. Not every sex act yields fertile eggs.

Candling

By looking at the eggs your bird has laid, you can sometimes tell whether there is a baby bird developing inside. This process is known as "candling" the eggs. You should candle the eggs about five to seven days after the parents begin sitting on them. Some birds start sitting on their eggs right away. Others start sitting only after some, or all, of the eggs have been laid. Watch to see how much time the parents spend in the nest. This will give you a good idea of whether anyone is sitting on the eggs. Ideally, the parents should have been sitting on the eggs for five days when you candle them. However, if you are trying to candle them at some other time, you can still learn something about what is going on inside the egg.

How To Candle Eggs

To candle your bird's eggs, you will need the following:

Something soft to carry the eggs in: a dish with a dishtowel folded in the bottom of it, perhaps.
A flashlight that shines a strong light.
Somewhere to put the parent birds: a pet carrier or spare cage, perhaps.
A room that is fairly dark.

Here is what you do:

Remove the parent birds into the pet carrier or spare cage.
Gently put the eggs in the dish or other egg carrier.
Take the eggs and flashlight to the dark room.
One by one, hold the eggs up to the light of the flashlight. Ideally, you should look at the egg with the flashlight behind it, so you see only the light that comes through the egg.
return the eggs to the nest and then return the parents.

Now you must interpret what you have seen.

Interpreting What You See

This is what you might see if you have a freshly laid egg. The egg has a small air space at the wide end. You may be able to make out the yolk, vaguely, as a yellow blur somewhere in the center. If the egg is over a week old and still looks like this, it is probably not fertile.

week-old fertile egg This is what you will see if your egg is fertile and is about 5 days old. Notice the fine lines, like red veins, that you can see when candling. They may be faint, but they are definitely there. This is the blood vessels of the developing chick. If you see this, congratulations! You have a fertile egg.

maybe fertile, maybe a bad egg An egg that is opaque like this one could mean a couple of different things. First off, it could mean the egg is fertile and the chick has developed to the extent that you can't see through the egg at all. A fertile egg that is over a week old starts to get opaque like this. Notice that there is still that little air space at the wide end. A day or two before hatching, the air space disappears altogether.
An egg that looks opaque like this one could also be an egg that is rotten inside, or an egg in which the baby has died. You can't tell, so leave the egg in the nest till it is far overdue for hatching!

old bad egg This egg is opaque, as the one we just discussed, but it has a large, off-center air pocket. It could contain a dead-in-shell baby, or it could be an old rotten egg.

old clear egg This egg is an old one that was never fertile. Nothing ever developed and so the egg stayed clear. The air pocket is too large and off-center.

So now what???

I recommend not throwing out any eggs that look like they have veins or that are opaque (provided the opaque ones have no large, off-center air pockets). Let them stay in the nest until after you think the hatch date has passed.

What If I Don't Want Baby Birds?

If you don't want babies to hatch from your birds' eggs, then you don't need to candle them. You need to addle them. Simply pick up the eggs and shake each one, hard, shortly after they are laid. This is like scrambling the egg in the shell. No baby will develop even if your birds are fertile and having sex. Once the parents have sat on the addled eggs for a few weeks, you can remove them

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Egg Candling: How to See If Your Birds' Eggs Are Fertile