For those most accustomed to seeing horses and donkeys at a farm or zoo, the concept of these animals in the wild might seem a little strange. A new study published in the journal Science has proven their resourcefulness as independent animals, as it found that when faced with little to no water they can simply go digging for their own. As well as keeping themselves alive, the resulting wells are of great ecological value to many other species – to the extent that their existence can even increase the surrounding biodiversity.
The study focused on feral horses and donkeys in the Sonoran Desert in North America, where they monitored four separate streams. The precious resource would flow freely in the winter, but come summer, they would dry up. Surveys across the summers of 2015, 2016, and 2018 revealed that feral horses and donkeys were able to overcome this obstacle by essentially digging a well.
“It’s a very hot, dry desert and you’ll get these pretty magical spots where suddenly there is surface water,” said study author Erick Lundgren from Aarhus University in Denmark to New Scientist. “These resources are in fact used by all other animals – there was a cacophony of organisms.”
After establishing a well of around 2 meters (6.6 feet) in depth, the animals would take their fill and leave the lifeline open to whatever wildlife needed it. Across their observations, the researchers saw 57 vertebrates other than horses and donkeys drinking from their handiwork, including quails, squirrels, and even a black bear. Interestingly, it’s not just animals who benefit from the DIY watering holes.
By returning water to dryland ecosystems, these wells support plant ecosystem processes too. The result is an uptick in species richness and ecological activity around the well sites compared to nearby dry sites, and even sometimes acting as a nursery for native trees.
“Equid-dug wells increased water availability, were used by a large number of species, and decreased distance between water sources,” wrote the study authors. “Abandoned wells also led to increased germination in key riparian tree species. Such equid-dug wells improve water availability, perhaps replacing a lost megafaunal function.”
There are still questions to be answered as to whether these wells affect all wildlife equally, or if they lean in favor of native or non-native species. The answer to this becomes increasingly important if donkeys are horses were to be introduced into dryland areas (which are becoming more common due to climate change) as a means of giving ecosystems a boost in the increasingly hot summer months. While increasing biodiversity is considered to be instrumental in tackling the climate crisis, further evidence is needed to understand exactly what effect sending in teams of well-digging hoofed animals could yield.
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