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Earth Notes: Well-Digging Wild Burros

Bureau of Land Management

Wild donkeys, also known as burros, first arrived in Arizona with early Spanish colonists, with many more imported by miners in the 1800s. They evolved from a North African variety and have tough digestive systems, allowing them to thrive in Arizona’s arid environment.


These burros can double their numbers every four years, so overpopulation eventually led to overgrazing of the landscape and predation by mountain lions and other animals, including humans.

It wasn’t until 1971 that Congress passed the Free-Roaming Wild Horses and Burros Act, aimed at protecting them as symbols of the American West.

These hardy animals have a unique skill that benefits other desert animals and plants: they can dig wells. Burros are known to dig down as far as six feet to find groundwater, creating an oasis for other animals. Researchers call this “contributing ecosystem services.”

A paper published last month in the journal Science cites a 3-year study of wild burros in several Southwestern desert locations, including western Arizona. It revealed that burros are frequent well-diggers. Many other animals were observed coming for a drink at these wells, including mule deer, big horn sheep, mountain lions, and several species of resident and migratory birds. Colorado toads also visited the burro wells.

Their populations continue to be managed by the Bureau of Land Management; the agency reduces  burros on public lands by the thousands each year by way of sterilization, helicopter removal, bait traps and adoption. Federal law prohibits euthanizing healthy unadopted animals.