The difficulty many finch breeders or hobbyists have is choosing which species to keep. There are very few people that will keep one species of finch and even those people that do, usually pick a species that has different color mutations. There can be problems with maintaining too many different species, however, if you have mixed colonies, not all species will co-exist in harmony. This sometimes takes some trial and error and a few plucked birds to figure out. Even if they do coexist, they will often interfere with each others breeding activities. Even mixing multiple pairs of like species can be trouble. Territorial species will sometimes fight to the death in the small area of an aviary. Unless you have unlimited cage space, the more species you add to your collection, the fewer numbers of each you can house and maintain. This can severely limit your ability to develop and sustain a line of birds. Yet, with all these disadvantages, few things are rewarding as having a mixed flight of birds coexist and produce their young in such a setting.