Audubon created 65 new images for the octavo edition, supplementing the original 435 in the double-elephant folio edition of 1827-1838. The resulting series of 500 chromolithographed plates constituted the most extensive American color-plate book produced up to that time. The Philadelphia printer J.T. Bowen reduced the double-elephant folio plates by camera lucida. The original configurations of the elephant folio were altered so that only one species is depicted per plate, and the resulting chromolithographs incorporated significant changes in the backgrounds and compositions. The text in the Ornithological biography was rearranged according to Audubon's A synopsis of the birds of North America (1839).  Digital facsimile from Biodiversity Heritage Library at this link.