Wild donkeys and horses dig wells that provide water for a host of desert species

A new study finds these equine wells attracted 59 other vertebrate species, boasting 64 percent more species than the surrounding landscape

by SMITHSONIAN MAGAZINE | 3 May 2021

Wild horses and donkeys are often considered a problem in the American West, but new research suggests their penchant for digging wells with their hooves offers benefits to the ecosystems they inhabit, reports Douglas Main for National Geographic.

The study, published this week in the journal Science, shows that when wild or feral horses and donkeys dig wells, they increase the availability of water for other species living in the parched desert landscape. These wells can be up to six feet deep and provide access to groundwater to species including badgers, mountain lions, deer and birds.

Donkeys and horses were introduced to North America roughly 500 years ago, and the Bureau of Land Management currently estimates there are more than 95,000 wild donkeys and horses roaming the West. That figure is more than triple what land managers say the landscape can sustain, and the growing population can “trample native vegetation, erode creek beds and outcompete native animals,” writes Jonathan Lambert for Science News.

In 2014, however, Erick Lundgren, a field ecologist at Aarhus University in Denmark, saw wild donkeys digging wells and wondered if other animals in the environment might use them in much the same way that animals from far and wide take advantage of elephant-dug watering holes in the African savannah, per Science News.

To investigate, Lundgren and his co-authors kept an eye on four dried-up streams in the Sonoran Desert of Arizona. The team monitored the streams during the summers of 2015, 2016 and 2018 and made note of any new wells dug by horses and donkeys.

Researchers found that the wells drew 59 other vertebrate species, 57 of which were seen drinking from the equine waters. Some wells even appeared to provide a boost to desert trees such as willows and cottonwoods, which researchers observed germinating from the moistened soil.

“These resources are in fact used by all other animals—there was a cacophony of organisms,” Lundgren tells Karina Shah of the New Scientist.

In fact, the team found that the average number of species around a horse or donkey well was 64 percent higher than in dry surrounding areas observed at the same time periods. Read more »

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Featured Image: © Petra Kaczensky