If you have talked with experienced breeders or even spent a little time on the Internet you've probably heard the term "candling" used when revering to checking a clutch of eggs for fertility.
Candling quite literally means: "to examine by holding between the eye and a light; especially: to test (eggs) in this way for staleness, blood clots, fertility, and growth"
You don't need any fancy equipment to candle your finch eggs. All you really need is a somewhat dark area, clean hands (very important), and a small flashlight or penlight. Simply put the light up against the shell. With the light source against the shell it lights up everything inside. If you are in a darkened area or room you should be able to see whether or not the egg is fertile with only a seconds glance before moving on to the next eggs. Sometimes you can do this with the eggs still inside the nest, other times you need to remove the eggs for a clear view.
Accessing the Eggs:
If you have a nest box that allows easy access to the eggs you can candle them inside the nest. This is the easiest way to candle them and it causes the least stress on the parents. If you use a covered bamboo or grass nest you will probably need to get the eggs out before you can candle them.
Some people use a small plastic spoon to scoop the eggs out; others gently roll the eggs out on to a tissue. Once candled the eggs can be returned to the nest in the same manor. Please remember that if the eggs are kept away from the parents to long they will get cold and die. Also note that once the eggs and nest are returned to the parents they may not jump back in to the nest readily.
Candling: when and what to look for.
Normally candling is done after 5 days of incubation. That is the best time to look for embryo development. The first few days don't work well because you wont see much. It takes time for the 2 cells to multiply in to something visible to the naked eye.
Around 5 days you should see small red veins, a little brownish blob and a tiny pulsing read dot in side the brownish blob. What you are actually seeing is the development of blood vessels from the chick to shell to allow oxygen in and carbon dioxide out. The vessels run to the chick (the brownish blob) and the tiny red dot is the newly formed heart already hard at work pumping blood. My crude animation to the right is a larger version of what you should see.
If you see only yellow yolk material you can wait a few days and try again. If there is still no development you know the egg is infertile.
If you'd rather not candle the eggs in the early stage of development you can wait until day 10. If they are still alive they should appear nearly solid and dark as the chick now fills most of the egg. If the area towards the bottom of the egg is dark and you see a large clear area above the chick has most likely died in the shell.
A word of warning:
Candling isn't without its risks. I do not recommend you candle the eggs of any finch pair that has yet to raise a clutch of chicks together. The first clutch is very stressful on the parents and you need to be out of the way as much as possible.
Risk #1: Nest abandonment. Not all finch pairs will want you to mess with the nest. For them it's an instinctive response to abandon the clutch once a predator (you) has found the nest. It is also very important that you always return the nest to the exact spot in the cage from where you took it.
Risk #2: The eggs get too cold. If you are messing around with the eggs and nest for more than 3 minutes, stop and return everything to the cage. If the eggs become to cold they will die. Candling should take only about 1-2 minutes from the moment to shoo the parents from the nest until you walk away.
Risk #3: Damaging an egg. This is always accidental but it does happen. Even the slightly hit or drop on to a hard surface can jar the embryo too much and kill it. A crack in the egg is instantly fatal for the embryo. Jarring the egg so much that the veins tear free from the shell will also kill the embryo but it'll take a day or two for the embryo to die.
Risk #4: Dirty hands. Even if your hands look clean they aren't. Your skin is always secreting a little oil and salt from your pours. This oil and salt can clog the tiny pours on the eggshell making it impossible for the chick to breath. Always wash and dry your hands before touching an egg and even then keep contact to a minimum.
When will they hatch:Each species will have slightly different incubation periods. If the eggs are fertile, not damaged and if the embryo survives; it will hatch in approximately 12-15 days. To narrow that estimate down a bit I will list the incubation for some of the more commonly kept species.
|Zebra ||13 days
|Gouldian ||15 days
|Java ||14 days
|Orange Cheek Waxbill ||12 days
|Red-Cheeks Cordon Blue ||12 days
|Red-Eared Waxbill ||12 days
|Society (Bengalese) ||12 days
|Tri-Colored Nun ||12 days
|Paradise Whydah ||14 days
|Orange Weaver ||14 days
|Blue-Headed Parrot Finch ||14 days
|Green Singer ||14 days