The Secret Lives of Well-Digging Burros
“Far-West Texas burros are eradicated by state and federal parks & land managers based on the belief that they “compete” with other wildlife for water. In reality – as this Arizona study explains – “it appears that burros are significantly increasing water availability in the desert.” Be sure and watch the video.
NOTE: this article was initially posted to Horsetalk.co.nz on June 5, 2016.
A researcher in the Arizona desert is unearthing hitherto unknown secrets about the remarkable well-digging exploits of wild burros.
Erick Lundgren, a PhD student in the biology program at Arizona State University, has used motion detecting game cameras in his research to learn more about the ability of burros to dig for water, and has also chronicled many other species taking advantage of the burros’ wells.
Lundgren, who has worked as a field technician in projects involving birds, mammals, and rivers over the last nine years, has focused his efforts on Arizona’s desert, where burros can dig wells more than a meter deep.
“Many species use these wells for drinking water,” Lundgren told Horsetalk.
“This behavior has never been described in the literature, likely due to prevailing negative attitudes towards introduced species.”
He explains how he first became involved in researching the water-finding prowess of burros, which is part of what he calls the unseen ecology of the species.
“Four years ago I was camping on a beautiful river in the Sonoran desert of Arizona,” he says.
“This river winds through a brutally gorgeous landscape that looks like melted wax; old multicolored volcanic debris, steep canyons, saguaros and cottonwoods.
“As a field biologist, I was becoming interested in how ecologists understand and describe invasive species.
“I was beginning to realize that to demonize a species because it doesn’t belong may prevent us from seeing what it actually does.
“It was on this trip that I began seeing, after years of working and camping on this river without noticing, these strange features – wells.”
What is a burro? In the Iberian Peninsula and the Americas, a burro is a small donkey. Burro is the Spanish and Portuguese word for donkey. In the United States, “burro” is used as a loan word by English speakers to describe any small donkey used primarily as a pack animal, as well as to describe the wild donkeys that live in Arizona, California, Oregon, Utah,Texas and Nevada.
Three years later, he had successfully documented the origin of these wells, and confirmed his suspicions: They were dug by burros.
“Burro well-digging has never been described in the scientific literature,” he says.
Lundgren says he is now doing his PhD research on this phenomena, which connects to a growing body of scientific thought that is shifting opinions on introduced species.
“From my preliminary data, it appears that burros are significantly increasing water availability in the desert.
“I have found sites that are very arid, with limited and intermittent surface water, where burro-wells maintain access to subterranean water throughout the year.”
He found that, in certain contexts, these burro-wells appeared to function as vegetation nurseries. He found that significantly more cottonwood and willow seedlings germinated in abandoned burro-wells than in adjacent riverbank zones.
Lundgren said a small grant from Arizona State University had enabled him to buy several trail cameras for his research. That enabled him to document 13 species using these wells, including bighorn sheep.
“I am surely missing many smaller-bodied species. In fact, javelina and cattle appear to use these wells at a greater frequency than even burros.”
Lundgren said his research was revealing a more nuanced understanding of burros.
“Not only is this relevant to the management of wild burros, but also to the paradigms which shape our understandings of ecological communities in general.”
Lundgren has faced challenges in carrying out his work.
Last year he launched a crowdfunding campaign on the Indiegogo platform to fund his ongoing work.
He raised $US4640 – well above his original target – which had enabled him to buy 12 game cameras and fund a crew of undergraduates to join him in conducting preliminary research through the summer of 2016.
Looking ahead, he says if he can raise another $US8000 he would be able to conduct the research full-time through the winter and summer of 2017 – work which he said would allow him to robustly answer the key questions around the burros’ water-finding activities and how they interact with their local ecosystems.
“I could,” he says, “use a million dollars on this research, but I’d be able to do a ton more with just $8000, as I would be able to collect data full-time, instead of just on weekends.
“Primarily, I need to map the distribution of this behavior, of these well-features, across the larger southwestern landscape to understand how common this phenomena is, and to what extent it influences the availability and persistence of water.”
Lundgren says he is currently in the midst of the field season for his burro research, as well as working a full-time field job which he took because he did not raise enough money to fund his living expenses over the summer.
“This summer I’m trying to understand the extent of this behavior – the digging of wells, and gain a better understanding of its importance,” he says.
He had seven sites he was visiting with the team of undergraduate volunteers three times this summer.
“We are quantifying the availability of water of different forms in these canyons – both natural sources and burro-well water.
“As the summer progresses, and surface water dries up, we are interested in quantifying how important burro-wells become in maintaining access to this limiting resource.
“We are also installing camera traps at each of these sites – on burro-wells, on natural water features, and on adjacent dry areas as natural controls.
“We are hoping then to be able to quantify how other animals use these burro-dug features relative to other spaces and resources.”
The team would also conduct experiments at each site to test how the availability of water through the burro-wells may alter food web dynamics.
“Many desert species can tolerate the absence of surface water because they can extract water from their food,” Lundgren explains.
“However, this leads to escalations in interactions – predators consume more prey, herbivores consume more green herbage versus senescent [older] brown herbage.”
This escalation in interaction strength, as ecologists term it, can lead to unstable population dynamics in both the consumed and the consumer, and to population collapses.
“To test how burros, by digging wells, influence this, we are conducting a ‘cafeteria’ experiment – offering invertebrate herbivores fresh leaves (high in water) and dry leaves in areas around burro-wells and in areas without surface water.
“The herbivores’ choice will indicate how water is driving their consumption decisions.”
Should he get enough funding to allow full-time research next summer, he hoped to employ a drone, instead of surveying on foot, to measure the availability of water through the entire season.
“I would then have the time to answer more nuanced questions – how do burro-wells influence the movement patterns of other desert species? How do communities of arthropods and rodents differ between areas with burro-wells and areas where burros are not present?
“Unfortunately, these questions cannot be answered without treating this research as a full-time job.”
Lundgren notes that burros, as an introduced species, were commonly described by the scientific community as “scourges”.
“Nearly all primary scientific effect-studies about them focus on how burros overgraze and outcompete native species,” he says.
He said these studies had failed to yield generalizable understandings because of weak methodologies and their failure to consider the ecological context of apex predator control.
Lundgren would welcome any further contributions via his crowdfunding page to help with future research into the well-digging and what he calls the unseen ecology of the wild burro.