White-rumped Munia..Lonchura Striata....
Here is the ancestor of our Bengalese Finches, it looks and behaves in exactly the same way...Once settled they are willing breeders, a generation or two later they are as easy to bred as our Bengalese...
But it's difficult to find many fanciers who want your offspring, they are not colourful, not tuneful or have any outstanding traits, but once you keep a few they will always be around in your birdroom....
Get a pair or two, preferably from me............