Audubon was a keen naturalist, but he had no formal scientific instruction and little art education, though some training in taxidermy, when he became deeply engaged in developing his skill at drawing birds in the 1820s. After he completed the 435 studies for his Birds of America, large folios of color aquatints published from 1826 to 1838, Audubon began work on watercolor studies for The Viviparous Quadrupeds of North America, a three volume folio of lithographs. For this project, he embarked on an extensive journey along the Missouri River into a region later known as the Dakota Territory to observe animals in their natural habitats and collect and inspect specimens, some of which he shipped live to his studio in New York. Audubon's drawings of small four-legged animals, such as this squirrel, are among the most beautiful of his watercolors from this project. The squirrel's alert black eyes, wiry brown hair and whiskers, and extended claws grasping the bark of the implied tree trunk exemplify Audubon's insistence on accuracy in depicting an animal's movement and appearance in a natural habitat.