Male and female society finches look pretty much the same. There's no real difference in size or coloring, so telling them apart can be problematic -- especially if you'd like a breeding pair. To determine the gender of your little birds, you must observe their behavior.
The Society Finch
Also known as the Bengalese finch, the society finch gets its name because of its friendly temperament when dealing with other birds. Like many finches, they aren't especially keen on people. These little birds bred easily and prolifically, so if you determine male from female and place them together, eggs and chicks should soon arrive.
Singing and Dancing
Male society finches sing, while female finches make little chirping sounds. Since males sing a great deal, it shouldn't take long for you to figure out the sex of a particular bird. While singing is a regular activity, males also perform a courtship dance for female finches. They bounce back and forth on a perch while ruffling their neck feathers and stretching their necks. The female, or hen, might make a warning sound if she's not interested in his affections.