Wild horses dig wells in deserts, providing vital water sources for other animals and plants, research reveals

While not as famous as beavers in terms of their ‘ecosystem engineering’, horses are now known to play an important role in some arid areas, writes Harry Cockburn

Wild horses in Arizona. Desert-dwelling wild and feral populations of horses and donkeys increase water availability for many other animals (Getty )

Horses are not well known for their engineering prowess, but maybe they deserve more credit, as new research suggests desert environments can be transformed by wild horses and donkeys’ ability to dig wells which also provide water for other wildlife.

A research team which studied populations of wild horses and donkeys in North America say the animals’ “ecosystem engineering” capabilities had been largely overlooked.

The authors said the animals were routinely found to hollow out wells up to two metres in depth, creating new oases in dryland ecosystems which were sometimes the only water sources locally available.

The researchers, led by Erick Lundgren, a postdoctoral researcher at Aarhus University in Denmark, said even those animals which are reintroduced to such environments, or were feral, can increase water availability in dryland environments.

The well-digging was found not only to provide vital water sources for animals including black bears, american badgers, rare birds and insects, but also for plants.

“Equid wells became nurseries for riparian trees,” the authors said, and suggested that horses and donkeys’ well building activities could even help these harsh environments become more resilient to ongoing human-caused aridification.

The researchers surveyed several sites in the Sonoran Desert in Arizona where there are already populations of feral horses and donkeys.

They found that as temperatures rose, the horse-dug wells played an increasingly important role in the ecosystem, and that overall they increased the density and reduced the isolation of water features in the landscape.

The wells provided up to 74 per cent of surface water by accessing the water table in dry reaches, and they increased water density relative to background water by an average of 332 per cent and by as much as 1,450 per cent.

In total 57 species were recorded coming to the wells to drink, including birds of prey, deer and bighorn sheep.

“We show that feral equids (horses and donkeys) can increase water availability in drylands, with associated effects on a variety of species and ecosystem processes,” the authors said.

“We suggest that well digging by feral equids may replace a function lost with the extinctions of large vertebrates across the world’s drylands.”

Large terrestrial herbivores such as horses “play crucial roles in their environments”, the scientists said, but since the late Pleistocene, megafauna have experienced drastic declines in abundance worldwide, which has led to the loss of many of their ecosystem functions.

Although megafauna declines have been linked to the formation of closed forests, increased wildfires and reduced plant seed dispersal in modern temperate and tropical environments, their impact on dryland ecosystems has been much less closely studied and understood.

The research is published in the Proceedings of the National Academy of Sciences of the United States of America.