Egg Fertility 1

There are a few ways to check if eggs that are laid are fertile one of the easiest methods to use, works best when there are some eggs fertile and some not that can be compared against each other. Once you have more of an eye for it it would be easier again.
Basically as an egg reaches maturity leading up to two weeks old an infertile egg which in Australia is often called a "Clear" egg, looks just like that. It has a kind of yellowy translucent look where the fertile eggs look significantly more solid and have a grey/blue tinge.

Above you can see the Three infertile eggs (clear Yellow) across the top and Two fertile eggs (solid grey/blue) across the bottom.

Sexing Bengalese 3

In this clip you can hear the Female Bengalese Finch (in the carry box) has a multi-syllable trill distance call and the male (off screen) has a single syllable call. The other sounds in the background are baby Bengalese. This is a good way to tell the difference between a Male and a Female Bengalese Finch (Society Finch) particularly if you have had a group of birds together for a period and they know each other you can separate one and depending on the type of distance call to its friends you can tell if it is a male or female.