Originally the Finch in the Galapagos Islands consisted of only one species. This finch was once used by charles darwin to develop his evolutionary theory, now proved to fit that theory.
Quote the medium-sized finch that Darwin studied, gradually shrinking its beak to obtain various types of grains. This change occurs after many larger birds come to become rivals for the finch, and compete for the same source of food.
What used to be just one type can now be of various species. Initially left large to small, some long-bred, initially feeding only one type into various grain eaters, insects.