Donkeys and Burros and Asses

Wild donkeys are Riverside's most charismatic animals. Also, at more than 4 feet tall and weighing over 400 pounds, burros are certainly Riverside's largest animals. Whether you see a few ambling along a roadside, a drove creating a traffic jam on Reche Canyon Road, an individual wandering along train tracks, a family nibbling on a neighbor's landscaping, a couple grazing on your lawn, or one pleadingly looking into the passenger-side window for a treat, the donkeys of the mountains and surrounding neighborhoods of Riverside, Colton, Moreno Valley, Loma Linda and Redlands evoke wonder and curiosity. They even have at least one Instagram site, @donkeysatucr.

Who are these guys?

First things first, are they donkeys, burros, or asses? Their English name is "donkey," and their Spanish/Portuguese name is "burro." Donkey and burro are synonymous. A burrito is a taco wrapped in a giant tortilla or a donkey foal. Donkeys/burros are part of a larger group of species known as "asses." Thus, it is not inappropriate to call a donkey an ass, especially one that is blocking the roadway.

That leads to the next question. How are our donkeys related to other asses and horses? The similarity of donkeys to horses is obvious. Nonetheless, they are separate species. In the eye of the beholder, donkeys could be characterized as "cute"; horses, "beautiful." Burros contrast with horses with long, jackrabbit-like ears, a long face, minimal mane, and a short, cow-like tail. Horses have much shorter, dainty ears, sporting a luxuriant mane and tail.

Horses and burros can hybridize up to a point. If a male burro (a.k.a. "jackass") mates with a female horse ("mare"), the resulting hybrid is called a "mule." Mules have legendary strength and endurance. They are also well known for their nearly absolute sexual sterility because their parents have different numbers of chromosomes preventing the production of functional sperm or eggs. From an evolutionary perspective, mules offer a Darwinian lesson. Despite the fact that mules are "fitter" in stamina, size, and performance than either donkeys or horses, the reality of their sterility means that they are evolutionary dead-ends.

For the other cross, when a male horse ("stallion") mates with a female donkey ("jenny"), their issue is called a "hinny." Like mules, hinnies are about as sterile as a brick. Thus, horses and donkeys are related enough to successfully mate but distantly so that co-mixing of the species is impossible.

Here's what the fossil record and DNA say. Four million years ago, the lineage that gave rise to modern horses, zebras, and asses (that is, the genus Equus = Latin for "horse") first appeared in the New World. The lineage spread around the world and gave rise to a LOT of species. First, true horses diverged from asses, and eventually, zebras evolved in sub-Saharan Africa. By the end of the Ice Ages, every continent except Antarctica had some Equus species, including horses in North America. About 12,000 years ago, the New World horses mysteriously went extinct (about 11000 years before they were reintroduced by the Spanish).

Jump halfway to the present. About 7000 years ago, the donkey (Equus africanus subspecies asinus) was domesticated from the Nubian wild ass (Equus africanus subspecies africanus) in northeastern Africa to be used as a beast of burden. The domesticated horse (Equus ferus subspecies caballus) was domesticated at about the same time as the wild horse (Equus ferus subspecies ferus), which was thousands of miles away in Central Asia. Interestingly, the numerous attempts to domesticate zebras have failed.

Presently, there are about seven extant Equus species: one horse, three asses, and three zebras. The species that contains donkeys includes two wild subspecies, the aforementioned Nubian wild ass and the Somali wild ass (Equus africanus subspecies somaliensis). These wild subspecies are highly endangered. In 2015, the total population of both subspecies was thought to not exceed 600 individuals, with a maximum of 200 adults. The two other ass species are also wild but not endangered: the onager (Equus hemionus) of Asian deserts and the kiang (Equus kiang) of the Tibetan Plateau. Both species are occasionally referred to as "half-asses". (No, I do not make this stuff up.)

To summarize, donkeys share a common, but distant, ancestor with horses. Both were domesticated millenia ago in the Old World. And both domesticated lineages were spread by humans around the world as useful animals. Both horses and donkeys have established free-living populations. Free-living, self-sustaining populations descended from domesticates are considered "feral".

Feral donkeys occur in Europe, North America, and Australia. Australia is home to about five million free-living donkeys, which are considered pests, destroying natural vegetation. However, in Europe and North America, they are protected. Feral burro herds occur in several states, and in California, they occur in several locations (including Death Valley and Big Bear), but only in the Inland Empire do they occur on private land.

How did they get here?

How donkeys came to the Inland Empire is controversial. Some contend that Gold Rush era miners brought them to the region, only to set them free when our local mountains proved fruitless for valuable ore. Another hypothesis is that a local rancher or ranchers rounded up some donkeys from the large free-living population near Death Valley and purposefully introduced them here in the 1950s. San Diego Zoo Wildlife Alliance's expert on the topic (and UCR graduate), Dr. Oliver Ryder, opines that donkeys would have been too valuable for miners to abandon; miners would have cashed them in. In his eyes, the intentional introduction 70-some years ago seems more likely.

Current status

Regardless of the specific circumstances that brought our burros to the Box Springs Mountains, here's what we do know for sure. Approximately 1000 donkeys live in the region now. That's more than the total number of their endangered progenitors surviving in Africa. These guys are no longer domesticated. They have lived and reproduced for several generations into a self-sustaining population.

For all practical purposes, these feral burros are wild and deserve respect. Although the burros are cute, they are neither pets nor are they the domesticated animals that were their ancestors. These are wild animals that have done damage to humans and vehicles. I have already heard a story of someone being bitten. Likewise, humans and vehicles have harmed burros. At the same time, even though burros are not native to the United States, they are protected by California law.

So give them some space. Drive carefully through the donkey habitat. Wildlife experts advise against feeding them so that they do not become overly comfortable with humans or (especially) with cars.

Do you want to do something to help our local burros? You should be aware of DonkeyLand Rescue (see Resources). Donkeyland is a volunteer non-profit charitable organization that rescues and rehabilitates sick, hurt, orphaned local wild burros and abused domesticated donkeys. If possible, they release the feral donkeys back into the wild. At the moment, DonkeyLand is focusing on their work. They don't have a visitor center or allow access to the public. Their website supplies information about their activities and provides an opportunity for donations.

How do we best enjoy our burros? They are fun to watch. Take pictures. Appreciate them as part of Riverside's natural diversity.

Many thanks to evolutionary geneticist and Kleberg Director of Conservation Genetics at the San Diego Zoo, Dr. Oliver Ryder, for directing me to the scientific literature on donkey evolution.