Almost all Society Finches are suitable as foster parents for exotic finches. The large European Society Finches are not suitable for this task at all, so forget it. They are reluctant breeders and often not good parents and would be totally unsuitable for consideration as foster parents for any exotic. However both American and Japanese Society Finches are quite the opposite, they are superb foster parents and they are also some of the best quality Society Finches you could ever own. The Japanese Selfs are fantastic birds, great markings and excellent breeders. I will not claim the are better foster parents than regular American Society Finches, but many have a nicer appearance in color and size, to me that makes them better choices for fostering.
I don't plan to write a thesis on the do's and dont's of fostering as that is not my interest or intent, but I will tell you what I believe. If you plan to foster exotics such as Gouldian Finches under Society Finches, well consider this. The timing of egg laying must be synchronized. That is to say the Gouldians and the Society Finches must lay their eggs at nearly the same time, so that when you replace the Society Finches eggs with Gouldian eggs they will hatch at the proper time. You cannot simply give Society Finches some eggs and expect them to start sitting on them. You cannot give Society Finches eggs that are ready to hatch if their eggs were newly laid. You cannot give Society Finches eggs that are newly laid if their eggs are ready to hatch. The timing is critical to success in fostering. The eggs you give the Society Finches must be the same age as the eggs you are removing from them. Trick to success at fostering, is to have minimally 3-4 pair of Society Finches for each pair of exotics you have need to foster. Now reasonably if you have 4 pair of Gouldians you might be able to get away with less than 16 pair of Society Finches, but the key is, you DO NEED, several pair of Society Finches breeding in hopes that one pair will be closely synchronized with the Society Finches.
I do recommend either American or Japanese Societies, especially the Chocolate Selfs as foster parents, you will have great looking Society Finches that are in demand, and superb breeders and foster parents. What more could you ask for.
Need to contact me, Email: Garrie@zebrafinch.com