As larger animals with a less efficient digestive system, burros (small donkeys) consume more vegetation than native bighorn sheep and mule deer. Damage to desert foliage can be extensive as they congregate near water during dry spells.
In the late 1800s, miners brought burros to the desert to carry supplies when they came searching for gold and other riches. When a miner died or moved away, often his burros wandered off and became adapted to surviving in the harsh desert environment. In summer, burros often devour leaves and branches as high as they can reach before stripping bark and perhaps killing the tree. Recently, we assisted Refuge biologists as they documented damage this invasive species has inflicted on desert vegetation at Imperial National Wildlife Refuge 40 miles north of Yuma, Arizona.
Beginning
When we set out, the December morning was cool enough to require jackets, but soon we shed the outerwear and endured temperatures escalating into the 80s. While Chuck placed flags to mark our direction and distance, I recorded statistics called out by zone biologist Brenda Zaun as she examined each designated bush or tree on one side of the flags. Bureau of Land Management (BLM) burro specialist John Hall and intern Allie Clifford checked vegetation on the opposite side. Imperial NWR biologist Joe Barnett assisted in the damage assessment.
Fresh tracks affirmed numerous burros in the area. Flies surrounded fresh burro droppings (scat) and puddles of fresh burro urine dampened the desert floor. We could smell them. We could hear them. But we never saw them. Shy and cautious, the burros vanished as we approached. We were the only humans for miles, the only threat to their security.
But we hadn’t come to view burros. Instead we concentrated on the harm they inflicted to the surroundings.
Damage
“Here’s some fresh bark stripping,” John called out. I handed Brenda the clipboard, pulled the camera from my pocket, and headed toward John to photograph the devastation he pointed out on one palo verde tree.
Frayed and broken limbs revealed more burro activity. The animals’ large incisors had ripped the tips from stems and stripped bark from branches. The biologists assessed damage by determining the percentage of branches affected on each tree or bush.
As we progressed along the washes, it became apparent that much of the vegetation was affected. Because burros are protected under the Wild Horse and Burro Act, hunting or harming them in any way is forbidden. Rounding them up and adopting them out remains the only viable alternative to reducing their numbers.
Until the next roundup, however, their numbers continue to increase, and the burros continue munching desert flora.
The Burros:
Burro Tracks:
Burro Droppings:
Burro Trail:
Chuck on McAllister Wash:
Biologist Brenda Zaun examining frayed branches:
Frayed Branch from Burro Damage:
Bark Stripping by Burros:
McAllister Wash:
Betty recording data; Chuck positioning flags:
John found a Deer Rack:
We worked up to the Yuma Proving Ground boundary:
