New tool models the future for wild horses on public lands

The U.S. Geological Survey and the Bureau of Land Management today announced the public release of a new modeling program designed to predict the potential outcomes of using various non-lethal methods to manage and protect wild horses roaming public lands. PopEquus provides realistic predictions that will help inform the use of various population-control methods to protect animal and land health from overpopulation.

“PopEquus is a ground-breaking new tool that will no doubt become invaluable to BLM field staff and managers as they compare different ways to manage and protect wild horses and their habitat on public lands, especially as drought and overpopulation continue to threaten animal- and land health,” said BLM Wild Horse and Burro Division Chief Holle Waddell. “The BLM is grateful for the hard work and determination that went into building PopEquus, and we look forward to continuing our collaborative partnership with the U.S. Geological Survey and other scientists and experts who share our goal of using the best-available science and technology to manage and protect healthy wild horses and burros on healthy public lands.”

“At the USGS, we sought to provide a science-based tool for wild horse and burro managers to inform their decision making,” said USGS Research Wildlife Biologist Kate Schoenecker, located at the USGS Fort Collins Science Center. “Being able to compare outcomes of various management actions and the financial costs of those actions can help managers consider and weigh trade-offs. We hope this tool will be educational for the public as well, as it shows the constraints and intricacies of managing wild horses and burros using real-life scenarios.”

PopEquus is open-source and uses peer-reviewed information to model expected outcomes for a given population of wild horses and the cost associated with that outcome. The model can project, for example, what the population size of a given wild horse herd will be after 10 years using a fertility-control vaccine to prevent pregnancy in a proportion of mares, as well as the expected cost. BLM managers can use this information to compare different possible management strategies.

The BLM manages and protects wild horses and burros on public lands as directed by the Wild Free-Roaming Horses and Burros Act. With few predators that can naturally control herd growth, wild horse populations on public lands can double in size every 4-5 years if not managed, which can quickly overwhelm available forage and water resources and damage the habitat for horses and other wildlife. As of March 1, 2022, the BLM estimated there were more than 82,000 wild horses and burros on public lands administered by the agency—more than three times what is sustainable.

The BLM is committed to using a variety of management tools to slow herd growth and reduce overpopulation across the West, including using more fertility-control methods to temporarily prevent pregnancy in a portion of a herd’s mares. PopEquus will provide additional analysis that will help BLM fulfill this commitment.

Visit for more information about PopEquus and the BLM’s efforts to use science and technology to improve management of wild horses and burros on public land

The Free Roaming Equid and Ecosystem Sustainability network will host a free public webinar April 5, 2023 to demonstrate PopEquus and answer questions about the model. The webinar will feature scientists from the USGS and BLM who helped develop the tool. To learn more about the webinar or to register to attend, visit the FREES website.

The USGS provides science support to Department of the Interior agencies to improve management of natural resources. Additional information about wild horse and burro population science can be found at: Wild Horse and Burro Population Management | U.S. Geological Survey ( or at: Search | U.S. Geological Survey (

To access the PopEquus user interface, go to the USGS web site: