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. A Donkey, 3 Rocks, and a Bird. A Donkey, 3 Rocks, and a Bird., also known as Donkey, Bird and Rocks and Donkey, Three Rocks, and a Bird, is an outdoor 1992 sculpture by Brad Rude, installed at Catlin Gabel School in West Haven-Sylvan, a census-designated place in Washington County and the Portland metropolitan area, in the U.S. state of Oregon. Brad Rude's "A Donkey, 3 Rocks, and a Bird." (1992), installed at Catlin Gabel School between the Lower School's science room and the Art Barn, is a cast bronze and stone sculpture depicting a life-size donkey and a bird