When I first got my finches the books said, "If you do not wish your pairs to mate, simply do not supply nest boxes, without them they will not mate."
Seemed simple enough - no nest boxes, no eggs. So in my large flight cage my dear birds were given a myriad of perches, three different bathing dishes, two fresh drinking water bowls, and multiple trays, dishes, and feeders each filled with fresh food. I made sure they had everything their little finch hearts desired - or maybe not.
One day I noticed that my female Cut Throat sitting in one of the food dishes and getting most upset when any other bird came near. It did not take long to realize that she was sitting on an egg. By that evening the male Cut Throat was brooding the nest (ie sitting on the egg). The next morning the hen was back and we had two eggs. This continued and soon we had three eggs. The only issue was this was not in a nest box. This was not a soft nest made with straw and leaves. This was a hard plastic dish.
Knowing they were new parents I waited until they were both out of the nest and put some alfalfa on the eggs. When they returned they quickly went to work arranged the hay into a nice nest. And they took turns brooding, with mainly the cock (the male) sitting on the nest. They were constantly being pestered by my Gouldians. In just a matter of days, the Gouldians had raided the nest and broken all the eggs.
Realizing that the birds were going to nest no matter what I bit the bullet and installed nests in the cage. Within 24 hours one pair of Gouldians had picked out a nest and started making it homey with alfalfa hay. It a matter of days we had eggs. They lay them a day at the time. The cock sat on them religiously. The hen would relieve him and take her turn. Often you would find both of them in the nest box. If any other bird attempted to get anywhere near the nest, the Gouldians fought them off.
(The pair of Gouldians in their nest)
(The male Gouldian)
Meanwhile the poor chickless Cut Throats were going in and out of the other nest boxes as if they were searching for a home. Finally they found one and started adding alfalfa to it, albeit a weak attempt.
(Cut Throat checks out new nest box)
So now I have a Gouldian pair brooding, I know, 3 eggs (maybe 4) and doing a very good job, a pair of Cut Throats making a second attempt, and the pair of Cordon Blues and Golden Breasteds are watching from afar with little interest.
Stay tuned. I keep reminding myself I did not want to get into the finch breeding business. But, as usual, I must remind myself, my life is out of my control.