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Invasive Wild Donkeys Are More Helpful Than Previously Thought

Donkeys are not usually thought of as invasive species, but, in the American Southwest, feral donkeys have become a nuisance and drain on the local environment. New research has found, however, that wild donkeys and equids of the American Southwest may not be as harmful to their surroundings as once thought. Wells dug by these creatures have come to be a much-needed source of water to local plants and animals alike.

Feral burros in Red Rock Canyon, western US ©Ecirphr/Wikimedia Commons
Feral burros in Red Rock Canyon, located in the western United States. ©Ecirphr/Wikimedia Commons

The Donkey Invasion Takes Hold in the Southwest

Although not native to North America, donkeys are found naturally in the deserts and savannahs of northern Africa, the Arabian Peninsula, and the Middle East. They were first introduced to North America by Spanish colonists in the 1400s as domestic donkeys bred from African wild ass. It was not until later on that donkeys brought to the American Southwest during the 1800s Gold Rush got loose or were abandoned by their owners and became feral.

Since wild donkeys naturally thrive in dry, arid areas, they adjusted well to life in the Southwest. These feral donkeys bred, and, as the population grew, they became an environmental problem, as invasive species tend to do. They ate up grasses meant for livestock and stole resources from native species.

To combat the damage being caused, the wild donkeys were then hunted nearly to extinction. For example, in Death Valley National Park, California, donkeys competed with bighorn sheep for the limited food and water in the area, almost wiping out the sheep population. In response, National Park Service Rangers shot around 400 wild donkeys between 1987 and 1995 as part of the park’s "Direct Reduction" policy.

After the slaughter of wild donkeys led to massive declines in their numbers, Congress passed the Wild Free-Roaming Horses and Burros Act of 1971. The act stated, “Wild free-roaming horses and burros shall be protected from capture, branding, harassment, or death, and, to accomplish this, they are to be considered in the area where presently found as an integral part of the natural system of the public lands.”

Once protected, populations began to grow again. Currently, the donkey population has reached levels that many consider to be out of control and even dangerous.

Growing Numbers of Feral Donkeys Lead to More Accidents and Environmental Damage

There are currently more than 95,000 wild donkeys and horses in the western United States. Each of these donkeys consumes around 6,000 pounds of forage a year. There is already minimal vegetation in the western US, so this amount of foraging significantly impacts the availability of food for native ground species. They also eat plant seeds, which means less food for birds.

Beyond nibbling up food meant for livestock and native species, donkeys can also be a danger to humans. In Arizona, the booming donkey population has led to thirty-six car wrecks in three years.

The herds have also impacted the geography of where they live. Compacted soil and trampled plants from hooves lead to increased erosion. Donkeys also destroy crops and tear down fences.

Fearless donkeys foraging for unconventional food. ©Elljay/Pixabay
Fearless donkeys foraging for unconventional food. ©Elljay/Pixabay

New Study Finds Wild Donkeys Build Wells, Helping Ecosystems

While feral donkeys have been getting a bad rap for decades, it turns out that they may not be as harmful to their environment as once thought. An early 2021 paper published in Science sheds some light on how donkeys create a better environment for the species they share a home with.

A researcher and co-author of the paper became interested in African elephants that dig wells to find water in dry areas where they live. These wells not only become a life source for the elephants and their herd but also for other species. The researcher, Erick Lundgren, a biologist at the University of Technology Sydney, wondered about the impact of donkey wells after noticing donkeys digging wells in 2012.

Curiosity led to observing wild horses and donkeys in the dried riverbeds of the Sonoran Desert in Arizona and California for three summers between 2015 and 2018. What Lundgren and colleagues found was similar behavior to those African elephants. The donkeys dug wells up to six feet in depth. They supplied a significant amount of water to local species (including black bears, badgers, Woodhouse's scrub jay, mule deer, mountain lions, and javelinas) throughout the area during dry periods.

In fact, during the driest part of the season, the wells dug by the donkeys and horses were the only water source. The wells increased the local surface water by fourteen times and became a boon to local wildlife. Areas with wells had sixty-four percent more species than other areas nearby, including 59 species other than donkeys. Most of those species took advantage of drinking from the wells.

Not only animals benefited from the new water sources. Surprisingly, many of the wells stayed intact for long periods of time, allowing river trees like willows and cottonwoods to sprout from the moisture.

Deeper Discussions Are Needed to Decide the Fate of Wild Donkeys

These findings have opened discussions about how ancient wild horses and donkeys may have helped other species before their extinction in North America more than 12,000 years ago. They have also challenged the conventional thinking that all invasive species are 100% detrimental to their new environments.

Others in the scientific community urge that the paper’s findings do not negate the harm that donkeys cause to ecosystems, overall. For instance, donkeys have been found to prevent other animals from drinking at watering holes. The herds have also lessened plant diversity, even if their wells act as growing areas for some species of plants.

One thing has become clear. If we are to make informed decisions on how to handle feral donkey populations adequately, more research is needed to determine the environmental benefits and detriments that feral donkeys bring to the western landscape.


*Alina Bradford has been a published writer for more than two decades and has contributed her insights to SafeWise, CBS, MTV, Life Science, and many others.


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