Horse outward similarity is an unreliable measure of relatedness. Besides the horse, there are six other species of genus "Equus" in the Equidae family. These are the ass or donkey, "Equus asinus"; the mountain zebra, "Equus zebra"; plains zebra, "Equus quagga"; Grévy's zebra, "Equus grevyi"; the kiang, "Equus kiang"; and the onager, "Equus hemionus". Horses can crossbreed with other members of their genus. The most common hybrid is the mule, a cross between a "jack" (male donkey) and a mare. A related hybrid, a hinny, is a cross between a stallion and a jenny (female donkey). Other hybrids include the zorse,
A Donkey, 3 Rocks, and a Bird. facing one another. The donkey has a rock balanced on its back, while the bird is both standing on a rock and balancing one on its head. The donkey has surfaces decorations, including glyphs and figures, and is coated in polychrome bronze. The bird is coated in blue, green, orange, red and yellow. The sculpture measures approximately x x . Its base is made of exposed aggregate concrete and measures approximately x x . One plaque on the base reads, . Another reads, . Inscriptions near the donkey's crotch displays the artist's last name, a copyright symbol, and the year