Aside from taking it to the vet and getting an x-ray (super cute image, but kinda expensive/time consuming if its not a specialized and/or exotic bird) one nifty trick people use is “candling” the egg.
This does necessarily mean using an actual candle to see through the shell–in fact an electric light would be much better. Its basically shining a light through the egg. But terms of brightness/intensity–think candlelight. Or just above candlelight. You want something clear/constant enough to see through the shell, but not insanely bright/hot.
There is a somewhat specific process you need to follow, though.
- Here’s one link to a site with some general information about it.
- Here’s another site on how to make a home made candler!
Please read the instructions and research it before doing it! Fertilized eggs are fairly delicate and easy to damage.
You can check after 3-7 days after being hatched.
If its a white shell it will be easier to see. Brown shells are thicker and harder to see through, so look later in the week.
What you should see: Fertilized bird eggs contain blood vessels OUTSIDE the bird embryos. As in, within the shell but outside (and connected to) the fetal birds body. Sounds creepy, but its actually pretty similar to our umbilical cord when we are in the womb.
**BTW, This is why people should NEVER try to crack a fertilized egg open if it’s not hatching on time!!! But that’s another story.
Anyway, if its fertilized but still very new, you will see said blood vessels throughout the egg, but no embryo yet, through the light. If it’s a little older, you will see the developing embryo in the center of the egg.
When candling, you can take the egg out for up to half an hour. Its a pretty safe process, just dont overheat, shake, or drop (!) the egg while doing it. The temp of a fertilized egg should be a few degrees below the normal 104 degrees F (40 degrees C) of the avian body temperature…so the ideal incubation temperature (for ,most eggs) is about human body temperature–98.6 degrees F. If you have an incubator it will be set to the exact temp.
So anyway do not remove it from the nest/mother/incubator for too long. But more importantly, don’t overheat it. While its ok–even healthy– for a egg to be a little below temperature for brief period of time, it should never be exposed to too much heat or humidity.
But besides that, its pretty easy, and you can do it every day! Take pics to record the size of the growing embryo. Its a fun, lovely process.