Is My Egg Fertile? Candle the egg!
Use a flash light on an egg to look inside for embryonic development. If a you or a hen has been incubating an egg for a few days, you can candle an egg to see if it is fertile or not. Hold your egg up to a candle or strong light like an incubator light and observe what you see inside: A fertile egg will have clear signs of development such as networks of blood vessels present, an opaque shape of an embryo at the larger end of the egg, and even movement within the egg.
A fertile egg with an embryo that has stopped developing will have a blood ring or blood streaks observable in the egg. Since the embryo is no longer viable, the blood vessels that once supported it have pulled away from it.
An infertile egg or yolker will look fairly clear, with no blood streaks, rings, or vessels.
Observe if your eggs float. Floating eggs are often infertile as the volume inside of the egg is not large enough for it to sink. As embryos form, eggs become heavier. Check for floating eggs: [3]
Wait until your bird eggs are a few days old and all possible embryos have developed. In practice, it is best to only move possibly fertile eggs every once in a while and never too often. Taking an egg from its incubator too early can stunt development and taking an egg too late in its development can hurt the chick inside.
Get a bowl of warm water. Be sure to use warm water in case your bird egg is fertile.
Carefully place the eggs in the water. Be gentle, as some eggs are very fragile.
Observe if your eggs float or sink.
Return your fertile eggs back to the incubator as soon as possible
