Animal artworks have led to a reliable source of income for zoos. Like true museum pieces, often copies are made of the originals, which may be stored.
Paintings by rare animals, like Tian Tian the giant panda, can be quite valuable.
"Painting provides great mental exercise," McKnight said. "If an animal doesn't want to participate, it's their choice. Among wolverines, for example, some want to paint while others don't."