Size of cage

Question
First I appreciate your answers to the many questions mentioned on the page... now mine....
I already have two pairs in a cage of 50cm wide x 90 x 60cm high and they have been breeding very well... is it large enough for me to add another pair

Answer
I would hold off on adding more birds yet.  Each pair can have up to 6 babies, so your cage could become crowded quickly!  Imagine going from 4 birds to 16!  I have a cage about that size that I use for breeding pairs; it's about the size you'd want for one breeding pair.  Keep in mind, for each pair, you should have 2 nest boxes.  That could be tricky to do.  Most people if they want to breed more than 2 pairs, use either a much larger cage, or sometimes an aviary.