I'd like to take a moment to talk about eggs. Finch eggs to be more exact although most of this information can be applied to all bird eggs. I receive questions about eggs in general as well as questions about finch behavior regarding their eggs frequently. I'd like to dispel some of the myths and clear up some of the facts here.
For starters, all shelled (This includes birds and reptiles) eggs are fertilized inside the females' body. If you want to know how they are fertilized please go to my 'Finch Sex - Mating' article. I don't know where the idea started that the female laid the eggs then the male comes over to fertilize them. That's what fish do, and we don't have fish, we have finches.
To put a little common sense into the mix lets think about an eggshell; it's quite hard. It's not air tight, but there is still no way any sperm is going to get though that shell. The egg must be fertilized before the shell is formed and the shell is formed as soon as the eggs surface touches the open air.
The shell acts as a protective layer around the growing embryo until it's ready to hatch. The protection that the shell provides to the tiny growing finch is really quite amazing, It's strong and secure and helps to keep the embryo warm while the parents are away.
The shell also allows the embryo to breathe, not in the sense that you or I breathe, at least not at first. Air is allowed to in and out of the shell so the developing chick can grow. The simple fact that the embryo needs to breathe leads us to our second most common myth.
If you touch the egg the parents will smell you and abandon the baby. That's not what happens. First we must realize that seed eating finches really don't have a very highly developed sense of smell. They don't need to smell their seed dinner; they need to see it. Now if you were handling vulture eggs, then yes the parents would probably smell you, but not to many people keep vultures.
The truth to the egg handling is that the oils and salt from our hands clog up the tiny holes in the shell in which the embryo is relying on to breathe. If the baby can't breathe, it'll die, and if it dies finches have been known to toss the dead eggs or simply abandon the whole clutch. If the eggs aren't handled much the baby may survive, but it's also very possible that the oils you did leave on the shell will begin to grow bacteria. The bacteria can then spread to the baby inside the egg, to the other eggs, and even to the parent birds causing illness and death all the way around.
If you do need to handle your eggs, and even I do on occasion, please wash and dry your hands before touching the eggs or nest.
Now you come home and find an egg of the floor of your cage. More often than not the egg is no good. If it was laid on the floor because your finches have no nest, you can pitch the egg. Saving it for when the pair does build a nest is just silly. The female will lay more. That's what they do. All female finches lay eggs with or without a male. Granted if there is no male around the eggs are never going to be fertile now are they. ;)
If you do have a nest and the pair had been sitting on eggs for a few days, then you come home to find one had been tossed, pitch it. It really doesn't do much good to put it back in the nest, especially if it fell more than 12 inches. Even if they don't look cracked or damaged they rarely survive the fall. Too much trauma is caused to the embryo and the shell itself that the chick will rarely ever survive. It's honestly easier to just throw the egg away.
Often, first time finch parents won't sit on their egg right away; don't panic, it's ok. Many species of finch won't even start incubating their eggs until the entire clutch is laid. This is normal. As long as the incubation hasn't started the eggs can remain dormant at room temperature for a week or more and still survive. Even if they don't survive the parent finches do need these learning experiences.
Now a brief section on the nest itself. A nest isn't a home without nesting material. It really doesn't take a lot of nesting material to build a proper nest. In fact many finches will over fill their nests with material if you let them. Once the first egg is laid you need to stop their supply of material or they may continue to build and bury the eggs, and a buried egg will not hatch.
The same applies to too little nesting material. If there is too little or no material in the nest to protect the eggs the parents will find it nearly impossible to keep the eggs at the correct temperature and the embryos will simply never develop.
If your finches are building too much or too little and are still laying eggs, it's best to remove the eggs and nest for about a month then let them start over. Their breeding, nesting, laying, and incubation cycles are quite dependant on their hormone levels and these cycles need time to stop and start again slowly or your finch will start to show signs of stress and possibly illness.
I've also received many e-mails from those who have a clutch of abandoned eggs which they want to save. If the eggs had been incubated and for some reason the clutch was abandoned, not incubated during the night, then the eggs are already dead. Throw them away. Once they have cooled off that much they die and there is nothing you can do about it. The parent finches can try again later.
If the eggs had never been incubated you can keep them at room temperature for a few days and place them under some foster finches if you have any. Not everyone has foster finches and they want to try to hatch to eggs themselves. To that I say simply, are you nuts? Granted if you have an incubator which rolls the eggs, keeps the temperature and humidity controlled you may actually get some to hatch. If you do, then you will be stuck hand raising these finches. Most attempts at hand raising finches fail.
You don't have a fancy incubator and still want to know if you can incubate the eggs yourself. The answer I always give is no. I do know a few people have done it, but it's rare. The eggs must be in the temperature and humidity controlled environment and then rolled several times a day without you touching them. Not an easy task. It's best to leave this job to the finches; they know what to do.
Eggs are a remarkable example of diverse evolution. Birds have been evolving right along with their means of reproduction (eggs) for a long time and the birds are one hundred times better suited to deal with the eggs than we are. The egg is wonderfully simple in its complexity. Be nice to it.