With no natural predators, wild burros can have a strong effect on the landscape of the Southwest United States. As of February 2012, there were an estimated 5,841 wild burros in the United States, nearly all of them in Arizona, California, and Nevada. These numbers are much smaller than the estimated 31,453 wild mustangs in the same regions, so the burros’ impact on the landscape of the Southwest is correspondingly less.
Type of impact
Wild burros graze on desert and semi-arid vegetation. In this capacity, they may compete with domestic cattle and sheep for the same land resources.
They also compete with the desert bighorn sheep (Ovis canadensis nelsoni) for vegetation and for water. However, the desert bighorn sheep is better adapted for extreme desert areas, such as Death Valley, and is no longer threatened by burros in these environments.
The hooves of wild burros can disrupt plant root systems. Where grazing is confined to limited areas, large numbers of burros can strip an area bare of vegetation.
Loss of vegetation leads to reduced vegetative mat. The soil in the area holds less moisture. Because burros do not preferentially eat shrubs, brush tends to replace succulent vegetation in that region. This can result in more severe fires, which further disrupt the local ecology.
Removal of root systems leaves the soil more exposed to erosion. Heavy rainfalls will wash away this soil, along with raised stream and river beds. This may eventually expose bare rock, which is incapable of supporting the same kinds of plant life.
In drought conditions, topsoil which is not held in place with a vegetative mat may be stripped by wind, which will permanently impoverish the soil and reduce agricultural yields. In extreme conditions, it may even lead to dust storms.
The wild population of burros in the Southwest is governed by the 1971 Wild and Free-Roaming Horses and Burros Act (WFRHBA), which declares them to be “living symbols of the historic and pioneer spirit of the West.” This Act protects them from branding, harrassment, or death, and tightly controls their capture.
The Bureau of Land Management (BLM) manages wild burros as part of the natural landscape and ecological balance. To this end, the BLM has identified Herd Areas (HAs) and Herd Management Areas (HMAs).
All regions which contained wild burros when the WFRHB was passed were originally HAs. HMAs are limited regions within HAs in which the GMA has decided external management of a wild burro population is necessary. After assessment of the region, each HMA is assigned a minimum and maximum burro population.
To reduce the wild burro population to sustainable levels, the BLM allocates a fixed number of burros for capture and taming every year. These burros can then be adopted by members of the public under the Adopt-A-Horse or Burro Program.