America's Wild Horses and Burros: Research for Management

In 1971, the U.S. Congress passed The Wild Free-Roaming Horses and Burros Act of 1971 in an effort to protect, manage, and control wild horses and burros on public lands. This legislation declared these wild animal populations to be "living symbols of the historic and pioneer spirit of the West." It vested the U.S. Bureau of Land Management (BLM)1 and the USDA Forest Service with responsibility for their management and directed these agencies to manage wild horses and burros for a “thriving natural ecological balance.”

Management of America’s wild horses and burros is a daunting task. Through its national National Wild Horse and Burro Program, the BLM manages about 33,000 wild horses and 5,500 wild burros roaming in 179 herd management areas, comprising almost 32 million acres in 10 western states. Management issues range from the effects of rapid population growth on habitat to ensuring healthy populations for the future. Largely unchecked by natural predators, wild horse populations often grow at rates of 18–25 percent per year. This unregulated growth can overtax vegetation and affect herd health as well as native wildlife populations.

Wild Horse History

The wild horses that roam the West are feral descendents of domestic animals that either escaped from or were intentionally released by early European explorers and later settlers. As a result of both origin and contemporary management, the Spanish or Iberian influence remains strong in some wild horse populations (e.g., the Kiger, Pryor Mountain, and Sulfur Mountain herds). In other populations, escaped or released military, saddle, and draft horses dominated by the Thoroughbred, Morgan, Quarter Horse, and draft breeds have formed broad zones of introgression (intermixing), sometimes with Spanish bloodlines. These populations of mixed ancestry increased to inhabit large areas of U.S. western rangelands.

Historically, the primary means of dealing with excess animals has been periodic “gathers.” Most herds are gathered (rounded up) every 3–5 years. Excess animals that are 10 years of age or younger are offered for public adoption; older animals are offered for sale to good homes. Excess animals that are not adopted or sold are maintained in long-term (pasture) holding facilities for the remainder of their natural lives.

In the late 1990s, the BLM entered into a partnership with the U.S. Geological Survey, Fort Collins Science Center (FORT) to design and implement a research program that would investigate alternative approaches for dealing with rapid population growth as well as other management challenges faced by BLM. A series of expert panels was convened to discuss the subjects of health and handling, fertility control, population estimation, genetics, and habitat assessment. Based on reports produced by these expert panels and information from a variety of other sources, BLM, FORT, and U.S. Department of Agriculture Animal and Plant Health Inspection Service staff prepared a Strategic Research Plan for wild horse and burro management. The plan initially focused on fertility control and population estimation, which FORT undertook as research projects.

Wild Horses and Burros Research
Arial photo of the Peaks Herd during a gather.

FORT projects directly or indirectly address BLM challenges in the areas of herd size and population management. As FORT researchers develop more accurate population estimation techniques and investigate the efficacy and impact of fertility control measures on herd behavior, the resulting findings and products will continue to provide BLM with the science necessary to guide decisions at the individual, herd, and landscape levels.

1We focus here on management by the BLM, our primary research partner.

Collaborators: 

Albert J. Kane, DVM, MPVM, PhD, USDA Animal and Plant Health Inspection Service

Dean Bolstad, Bureau of Land ManagementNational Wild Horse and Burro Program

Bruce Lubow, Ph.D., Natural Resource Ecology LaboratoryWarner College of Natural ResourcesColorado State University