How can I tell if the eggs are fertile?

1) Wait until the birds have been sitting on the eggs for a about a week.

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2) Hold them (the eggs, not the birds!) against a bright light (like a light_x000D_
bulb).

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3) If they seem clear ("transparent"), then they are no good. If you see_x000D_
small veins, or the egg is dark, then the egg is probably fertile: put it back and wait._x000D_
If the egg has been dark for a longer time than the expected incubation period, the chick_x000D_
could have died in the egg or you could just have a rotten egg on your hands (so to_x000D_
speak), and you will have to discard the egg. It is best, however, to wait quite a while_x000D_
before doing so unless you have a lot of experience looking at eggs or are really certain_x000D_
of how long the birds have been sitting on the eggs. The normal incubation period of_x000D_
domesticated zebra finches is around 13 days. Zebra finches usually start roosting when_x000D_
the third egg is laid.
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