Quirks & Quarks

Wild donkeys and horses dig wells in the desert, and create a refuge for plants and animals

The animals dug up to a metre and a half in order to access groundwater in the arid environment.

Researchers called the animals 'ecosystem engineers'

Wild donkeys in the process of digging a well in the Sonoran Desert in Arizona (Erick Lundgren)

Researchers have studied how wild horses and donkeys dig wells in the Sonoran Desert in the southwestern United States to provide themselves with water. In turn, the wells also provide for numerous other animal and plant species.

Erick Lundgren, a field ecologist at Aarhus University in Denmark, was one of the authors of the study.

There are an estimated 95,000 wild horses and donkeys in the western United States. Several thousand roam the Sonoran Desert of Arizon. In 2014 Lundgren first observed wild donkeys digging wells for themselves in the Arizona Sonoran, and wondered if other equally thirsty animals were taking advantage of the new-found water resource. 

Many animals, including these deer, reap the benefit of wells dug by donkeys and horses (Erick Lundgren)

Sniff, dig, drink

Donkeys and horses are surprisingly efficient at digging, and this activity has been observed around the world, but rarely studied. They use their front hooves as shovels to dig away at the desert's soft sand near dry creek beds, where there is a greater chance of finding water.

Sometimes they return to a site that yielded water in the past. But Lundgren has also observed donkeys and horses sniffing the ground for sources of water. Some of the wells observed for this study were a metre and a half deep, and there have been reports of wells as deep as two metres. 

Popular watering holes

Those wells were visited by a total of 57 different species. This included bobcats, wild sheep, wildcats, birds, and even a bear in one case. 

Plants and trees also benefit from these wells. Desert trees like willow and cottonwood grow in the newly moistened soil. In effect the donkeys and horses are creating multiple oases in the desert.

This tree grows in the soil made moist by a well dug by a wild horse or donkey in the Sonoran Desert (Michael Lundgren)

This well digging behaviour has also been observed in Africa, Australia, Brazil, and even among the wild horse population on Nova Scotia's Sable Island.

This bobcat was one of 57 different species to drink from a well dug by a donkey or horse (Erick Lundgren)



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