For thousands of years, horses and donkeys have been among the most important partners of humans. A new study released Thursday shows they are also a great help to desert animals and plants, digging deep wells that provide them with a vital water source, especially during peak summer.
Biologist Erick Lundgren, lead author of this research published in the prestigious journal Science, told AFP that he first noticed this phenomenon when he was working in the western US state of Arizona, where at the time he was studying the network of rivers.
“People didn’t think it was worthy of scientific attention,” says the researcher, who now works at Sydney University of Technology.
He had previously read about African elephants digging wells, which sometimes turn out to be the only source of water for other animals during the dry season. And he wanted to know if equines could play a similar role in America.
An intriguing idea, “because donkeys and horses are considered agents harming biodiversity”, not being species native to the region, he says.
For three summers, he and his team observed several sites in the Sonoran Desert, which stretches from Arizona to California.
They compared the contribution of wells dug by equines compared to the water available on the surface for the animals, which comes from sources that are sometimes permanent, sometimes intermittent depending on the season.
They also installed cameras to observe how other animals were using them.
– Two meters deep –
Their results show that these wells, which are up to two meters deep, have increased the amount of water available for many species native to the desert, and reduced the distance between large water points during dry periods.
During the hottest times of summer, they even proved to be the only source of water at some sites.
According to Erick Lundgren, equines thus serve as a “buffer” reducing the extreme variability of water sources from one year to the next.
The wells “were used by almost any species you can imagine, including some surprising ones like black bears, which you wouldn’t expect to see in the desert,” he explained.
Also seen drinking: lynxes, species of birds or wild pigs.
Some tree species have sometimes started to grow in abandoned wells, which shows that they also have a beneficial effect on the flora.
– “Invasion” –
Horses and donkeys were brought to America by Europeans to help colonize the continent, but many were later abandoned with the advancement of combustion engines.
Since then, they have been studied under the biological concept of “invasion”, explains the researcher, that is to say that they are not considered to be part of the local fauna.
But this reasoning is too closed-minded and has prevented scientists from having a more nuanced understanding of their effects on the ecosystem, he considers.
He says these wells will become even more important over time, as human activity and global warming reduce the number of perennial water sources in these regions.
Moreover, this behavior in horses and donkeys could have a “precedent” in history, according to Erick Lundgren.
Equines, elephants and other large animals that once roamed North America, until a mysterious extinction 12,000 years ago, may have played a similar role.