The Nesting Box:
One of the key factors for a successful breeding cycle, is certainly the nest
box, and a perfect one should meet two important criteria..
1- Shape
2- Size
Shape:
Gouldians are cavity nesters, which means that they need a closed space to make a nest and raise a family. Most shapes are acceptable, but you should go with the simplest of designs like rectangular (horizontal and vertical) and cubic.
Some nests have entrance holes and others have a larger rectangular shaped entrance. I've found out that Gouldians don't have any preferences towards the shape of the entrance because if it is too big for their likings, they will close some of it with nesting material.
Try not to go for the wicker baskets you find in pet stores, because for once they make it hard to check on the breeding progress, whether it is for candling the eggs, banding chicks or any other task. Another problem with wicker baskets is that for most of them they are too small, which leads us to the second criteria.
Size:
I don't want to use the cliché here, but it does matter. Gouldians mate inside their nests, and a tight space would make it impossible for the male to properly "do his job", causing the hen to lay infertile eggs. If this hurdle was overcame by the parents, and they somehow managed to lay a fertile clutch, the space is too uncomfortable for the growing chicks to develop properly, and it is not uncommon for the breeder to find the younger chicks thrown out from the nest by their larger siblings.
Overly larger nest are no picnic either. I am pretty sure the male Gouldian trying to make the box welcoming for his mate and future babies, doesn't appreciate it either. The poor thing has to make a small concave area in a big space where the female has to lay and brood. Not all males are accomplished builders, and a lot of them won't finish properly the nest causing the eggs to end up scattered inside the box, or squeezed against the corners. Needless to say that they won't get enough incubating and won't hatch.
So what should you use? Easy: Go medium, and by medium I mean, try to use anything close to the boxes I have drawn below.
I know that some would contact me to tell me that they have used larger or smaller nests with success, but these are the types I got the best results in, the rest is up to you.
New design: