John James Audubon was a French American ornithologist, naturalist, and painter. He is known for his expansive studies to document all types of American birds and for his detailed illustrations that depicted the birds in their natural habitats. His major work, a color-plate book entitled The Birds of America (1827–1839), is considered one of the finest ornithological works ever completed. This monumental work consists of 435 hand-colored, life-size prints of 497 bird species, made from engraved copper plates of various sizes depending on the size of the image. Audubon developed his own methods for drawing birds. First, he killed them using fine shot. He then used wires to prop them into a natural position, unlike the common method of many ornithologists, who prepared and stuffed the specimens into a rigid pose. When working on a major specimen like an eagle, he would spend up to four 15-hour days, preparing, studying, and drawing it. His paintings of birds are set true-to-life in their natural habitat. He often portrayed them as if caught in motion, especially feeding or hunting, basing his paintings on his extensive field observations. Audubon's influence on ornithology and natural history was far reaching. Nearly all later ornithological works were inspired by his artistry and high standards. Charles Darwin quoted Audubon three times in On the Origin of Species and also in later works. Despite some errors in field observations, he made a significant contribution to the understanding of bird anatomy and behavior through his field notes. Birds of America is still considered one of the greatest examples of book art.