To rearrange my aviaries, I need to put my gouldian and firetail finches in with my zebra finches. They won't breed with each other will they? What are the chances that they will, and what kind of mutant offspring would they have if they did? In other words, how concerned should I be about mixed breeding? Not all the gouldians have a mate.
They shouldn't as long as you have an equal ration of hens to cocks. My friend had this problem where the hen's outnumbered the zeb cocks and she ended up with a chicks from a Zeb (H) x Bicheno (C) & Zeb (H) x Gouldian (C).
Just something to think about....however, this is the only time I've heard of it happening and mine have never even attempted it so you should be fine