Wild horses and donkeys digging wells increase water availability in desert areas, study finds
Wild equines (horses and donkeys) reintroduced to desert regions of southwestern North America routinely dig wells to expose groundwater, increasing water availability – and sometimes providing the only water available locally – for a wide variety of plant and animal species and ecosystem processes, according to new research from Sydney University of Technology and Aarhus University.
Well dug by wild donkeys (Equus africanus asinus) in the Sonoran Desert, United States. Image credit: Lundgren et al., doi: 10.1126 / science.abd6775.
“Water is the main limiting resource for dryland ecosystems. It determines species composition, food web structure and vegetation dynamics, ”said Dr Erick Lundgren of Sydney University of Technology and Aarhus University and colleagues.
“Yet the ability of animals to improve water availability by exposing groundwater has received little attention.”
“Wild donkeys (Equus africanus asinus) and horses (Equus ferus caballus), along with most other equines and all elephant species, regularly dig wells up to 2 m deep.
To assess well digging and its associated ecosystem effects, Dr Lundgren and colleagues studied four groundwater-fed streams in the Sonoran Desert every 2 to 4 weeks for three summers.
They observed the digging of wells by the region’s wild equines (horses and donkeys) and found that the wells designed by the equines increased the availability of water for a number of native desert species.
“The rivers were 7 to 32 km apart and were 300 to 1,800 m long,” they said.
“Like many desert streams, the hydrology of the site was highly variable, as was the relative contribution of equine wells.”
“Equine wells were particularly important for the water supply in mid-summer as temperatures rose and water tables receded.”
“In a totally intermittent stream that lost all bottom water, equine wells provided 100% of the surface water. “
“Even on sites that have remained perennial (bottom water retained at upstream sources), the wells provided up to 74% of surface water by accessing the water table in the dry sections.
“Likewise, equine wells increased water density relative to bottom water by an average of 332% and up to 1,450%.”
Well-dug megafauna contributes to the ability to buffer water availability in many drylands. Image credit: Lundgren et al., doi: 10.1126 / science.abd6775.
To understand whether equine wells are of value to other species, scientists set up camera traps at five sites in the Sonoran and Mojave deserts.
Overall, they detected 59 vertebrate species in equine wells, of which 57 were recorded drinking.
“Digging a well also influences the vegetation,” the authors added.
“On a perennial river in the Sonoran Desert, dyked, abandoned equine pits shelter numerous riparian trees, members of a small-seeded, fast-growing and flood-adapted functional group whose germination requires a moist substrate without vegetation. competing and whose conservation is considered a regional and global action. priority.”
“We show that wild equines can increase water availability in drylands, with associated effects on a variety of species and ecosystem processes,” they concluded.
“We suggest that digging wells by wild equines could replace a function lost with the extinctions of large vertebrates in the arid areas of the world.”
The to study was published in the journal Science.
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Erick J. Lundgren et al. 2021. Equids engineer desert water availability. Science 372 (6541): 491-495; doi: 10.1126 / science.abd6775