The Salt River horses need management. The current contract is up, and the Arizona Department of Agriculture has posted the “Request for Proposal” for all interested parties. Below you will find a copy of the Request. Of note are stipulations #2 & #3.
2. Humane Management Plan to reduce herd size to a level to maintain herd health, herd and public safety, genetic and age diversity, as prescribed by the overall range ecology. The management plan shall include a suggested herd size goal and the time frame for meeting the herd size goal. The herd is approximately 280 horses that currently reside in the area defined by the Tonto National Forest as the Salt River Horse Management Area (currently 19000 acres). Any herd size reduction shall be accomplished through natural attrition, humane adoption and a birth control program.
3. Create and administer an equine birth control program designed to reduce the population of the SRHH. Any natural increase in herd size shall require the removal of existing animals at a 3:1 ratio. For every foal born, 3 adult horses shall be removed within 180 days of foal birth confirmation. This reduction must be achieved through humane adoption verified by AZDA staff until the goal herd size is achieved.
The removal of three adults per foal born seemed extreme, so I decided to run some population projections in R-Studio. Using the SRWHMG’s end-of-2024 population (282), we calculated year by year how the population would be reduced if the three adults per one foal were implemented.
According to the SRWHMG Annual Report, there were 282 horses at the Salt River at the end of 2024. We added a modest amount (ten) to account for foals and possible reservation horses. Using this number, we will predict the population over the next ten years, accounting for average use PZP, supplemental feeding, migration of reservation horses, and drought conditions predicted for Arizona for the next ten years.
The Salt River horse population over the next 10 years, incorporating:
- Starting population: 292 horses (end of 2024)
- PZP efficacy: average (assume 75%)
- Foaling rate: 1 foal per fertile mare per year
- Mortality rate: 6% (slightly elevated to account for drought conditions despite supplemental feeding)
- Removals: 3 adult horses removed for every foal born
- Reproductive mares: 50% female × 70% of those of reproductive age = 35% of population
- Migrants: Neighboring Reservation Horses can move back and forth in and out of the Salt River territory. They must be accounted for, and we utilized random movement. We made calculations with and without migrants. For the purposes of this dataset, we will make the reservation horses non-breeding, although they may not be treated with PZP, and therefore fertile.
For the nerds amongst you… here is the R Code
In 2019, the Salt River Horse Collaborative was formed and the members sought to mange the horses in the Tonto National Forest. Special interest groups and government agents were included.
The Salt River Horse Collaborative was established to develop a long-term management plan for the Salt River wild horses in Arizona’s Tonto National Forest. Facilitated by the U.S. Institute for Environmental Conflict Resolution and CONCUR, Inc., the Collaborative included a range of stakeholders:
Wild Horse Advocacy Groups: Such as the Salt River Wild Horse Management Group (SRWHMG) and the American Wild Horse Campaign (AWHC), both of which emphasised humane, non-lethal management strategies
Federal, State, and Local Agencies: Notably, the U.S. Forest Service and the Arizona Department of Agriculture.
Neighbouring Tribes: Tribal representatives from adjacent communities.
Conservation Organizations: Including the Center for Biological Diversity, which advocated for significant reductions in the horse population to protect native ecosystems.
Ranching and Hunting Interests: Groups concerned about land use and resource competition.
According to the report from the Salt River Horse Collaborative Meeting, the land can only support 28-44 horses. However, the majority of the parties involved agreed that 100 horses were sustainable. Please read the full report in the download below. However, none of this effort has been put into practice yet.
Revisiting this graphic below, we find that the horses, assuming no reservation horses ever set foot on the Salt River, would be at the recommended 100 horses by approximately 2028. The RFP states that if a horse leaves the management area, it will be removed upon its return to the Salt River. It also includes fence maintenance which neatly solves the issue of reservation horses
“9. If a horse leaves the herd containment area it shall no longer be considered part of the SRHH and shall be removed from the management area upon their return. Respondents shall propose a method for tracking horses that leave the containment area and return.
8. Maintenance of the fence forming the perimeter of the herd management area“
This is tenable, without a mass round-up, although the current management group is protesting this fiercely as would be expected. Given current estimates indicating that the Salt River horse population far exceeds the area’s ecological carrying capacity, implementing science-based management strategies—such as fertility control, active population monitoring, and controlled removals—is essential to preserve the long-term health of the ecosystem. Lower horse numbers are more sustainable for the degraded rangeland and promote healthier horses, reducing disease risk, starvation, and resource conflict. Responsible management ensures that future visitors can still enjoy observing wild horses in a more balanced and thriving landscape. Collaborative efforts among stakeholders are critical to achieving this equilibrium between conservation, animal welfare, and public interest.
Dr. Meredith Hudes-Lowder
May 5, 2025
