One factor that has a fairly significant influence, though less so than it is for historical prints, is the historic importance of the print or printmaker. Mark Catesby’s Natural History of Carolina, Florida and the Bahama Island was the first natural history of American flora and fauna and thus the prints by Catesby have considerable significance. These prints sell for a fairly high price for a number of reasons, but this is probably the most important. Prints by other major figures in history of natural science, such as those by Georg Ehret or Alexander Wilson, also have a fair bit of their value from their historic significance.
For most natural history prints, however, this is not that big a factor in determining their value. Much more important is their “decorative value.” This has a number of aspects, one of which is how “pretty” or visually appealing they are. Flower prints with lots of “petal power,” birds with bright colors, like cardinals or blue jays, or “cute” animals like rabbits all sell for a premium, while weedy looking plants, plain gray birds, or “nasty” animals like snakes or warthogs will sell for a discount compared to other prints.
There is more to the decorative value than simple visual appeal, for the quality and complexity of the design and printmaking also is a factor, and size too does matter. Smaller prints generally sell for less than bigger prints. Most flower prints are medium sized (in the range of about 10” x 16”), but lots of people want prints that have more impact, so larger botanicals like those by Basil Besler or Robert Thornton sell for a premium. There are very few natural history prints of really big size, so those that are sell for quite a bit more; examples are the Audubon imperial folio quadrupeds and even more the Audubon double-elephant folio bird prints.
In line with this is the negative “grossness” factor that turns up mostly with animals, but also in other natural history prints. As many naturalists tried to show their subjects in a natural setting, the scenes are sometimes such that many people find them off-putting. An example is the Audubon print of the Texas Lynx. Being from Texas, this print would generally be popular and the lynx is the type of animal many people find appealing. However, Audubon shows the lynx licking itself and this does not make this print dining room ready! Similarly, the wonderful print by Alexander Wilson of the black vultures standing over the body of a dead sheep. This is as important and colorful as any other Wilson print, but it definitely is the hardest to sell and sells for less than any other by Wilson.
One final factors in natural history prints is a “value ranking” for birds, animals and plants (similar to the value ranking of maps and views). Within each of these categories, some subjects are more popular than others and so will sell for more just for that reason. Cardinals are very popular and so are herons, woodpeckers and parrots. All of these sell for more than other birds (that is, a print in the same series of a cardinal will almost always sell for more than, say, a junco). Some of this is, of course, that these tend to be pretty birds, but it is more than that, for two prints can be just as attractive as each other, but if one is a woodpecker it will sell for more than a goshawk. With birds, one value ranking factor is whether the bird is extinct, for prints of extinct bird (Carolina parakeets and passenger pigeons) sell for more than birds that are not.
For animals much of the popularity comes from cuteness, but there are other factors as well. Some animals are just popular (bears, buffalo, moose) while others not so much so (skunks, wolverines, caribou). Flowers do tend to sell by “petal power,” but roses and especially tulips are by far the most popular, and thus expensive, selling for significantly more than daffodils or chrysanthemums. If you take a look at a price listing for prints from the same series—where they are all by the same process, with about the same amount of color, with the same historic significance, etc.—you will see these value rankings shape the prices. There are 435 different plates from Audubon’s folio Birds of America; the prints differ in terms of the size of the images, but within those prints that are of similar size image, the price is to a great extent determined by the bird's "value ranking."