Wild donkeys and horses engineer water holes that help other species
Often cast as invasive pests, the equids may actually benefit some ecosystems
![a kulan digging a hole in the ground](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2021/04/042921_jl_donkey_feat.jpg?fit=1030%2C580&ssl=1)
Donkeys and other equids are known to dig wells in dryland areas in search of water, like this kulan in central Asia. In the American southwest, new research suggests that wells dug by feral donkeys and horses can benefit the whole ecosystem by increasing water availability during dry times.
© Petra Kaczensky
Water drives the rhythms of desert life, but animals aren’t always helpless against the whims of weather.
In the American Southwest, wild donkeys and horses often dig into the dusty sediment to reach cool, crystal clear groundwater to quench their thirst. New research shows this equid ingenuity has far reaching benefits for the ecosystem.
Equid wells can act as desert oases, providing a major source of water during dry times that benefits a whole host of desert animals and keystone trees, researchers report in the April 30 Science.
Introduced to North America in the last 500 years or so, wild donkeys and horses are often cast as villains in the West. These species can trample native vegetation, erode creek beds and outcompete native animals. But when Erick Lundgren, a field ecologist at Aarhus University in Denmark, first observed wild donkeys digging wells in 2014, he wondered whether these holes might benefit ecosystems, similar to the way elephant-built water holes can sustain a community in the African savanna.
![a doe and fawn leaning down to drink water out of a hole in the ground](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2021/04/042921_jl_donkey_inline1.jpg?resize=680%2C383&ssl=1)
“Because of the way we value [feral] horses and donkeys, the orthodoxy tends to focus on how they harm ecosystems,” he says. “We wanted to see whether these holes provided a resource when water is scarce.”
First, Lundgren and his colleagues had to see whether these holes actually increase accessible water. Over the course of three summers from 2015 to 2018, they mapped out the surface area of water in wells and groundwater-fed streams at four sites in Arizona’s Sonoran Desert.