Introduction

Craig Downer’s article, “Protect the Wild, Pure Horses of the Salt River: End the Slaughter and Imprisonment of America’s Wild Horses,” is not a scientific study of the wild horses of the Salt River; it is an advocacy essay written with performative scientific jargon to create an impression of expertise. The article does not include any population-viability studies, any genetic information or studies, any estimate of the effective population size (Ne), any quantified studies of the effects of tourism, or any habitat-capacity studies to support his claims regarding the need to reduce the current free-roaming wild-horse population from approximately 125 horses to whatever number would be “sustainable” in his professional opinion. In his essay, Downer states that 125 horses would be “genetically nonviable” in his professional opinion (Downer, 2026). Link to Mr Downer’s essay at the ‘Friends of the Salt River Wild Horses’

125 Horses – Are They Genetically Nonviable?

The size of the census population does not in itself indicate whether a population is genetically viable or not. A number of factors can affect the effective population size (Ne). For example: the number of mares and stallions that actually breed in the population; whether or not there is unequal breeding success by the stallions; whether or not there are related animals breeding in the population; the age and sex distribution of the population; the degree to which different family lines are represented in the breeding stock; whether or not the population has previously experienced a bottleneck; whether or not there is migration into the population of unrelated animals; and whether or not there is implementation of fertility control, and if so, how is it distributed throughout the population.

• The number of mares and stallions that actually reproduce (for example, only a fraction of stallions may get to breed mares.
• Unequal reproductive success among stallions
• Relatedness among breeding animals;
• Age and sex structure;
• Representation of different family lines;
• Previous population bottlenecks;
• Migration or introduction of unrelated animals; and
• How fertility control is distributed across the population.

Downer does not present any data on measures of genetic diversity such as heterozygosity, allelic richness, inbreeding coefficients, Ne, a pedigree for the horses, or an estimate for the amount of genetic decline that will occur as the population size declines to 125 horses. Downer claims that approximately 125 horses would be ‘insufficient’ before he would conduct an analysis to answer this question (Downer, 2026).

The number of individuals used to determine whether a population is genetically viable (e.g., Ne) is typically much smaller than the total number of animals counted in a population census (Frankham et al., 2014). For the purposes of species conservation, two key guidelines have been put forth. The first is that the effective population size (Ne) must be greater than or equal to 100 to prevent a high amount of inbreeding over the short term. The second is that the effective population size must be greater than or equal to 1,000 to allow for a population’s long-term evolutionary potential (Frankham 2010).

These numbers are minimum numbers to keep immediate inbreeding to a minimum and do not mean that all populations less than these numbers will go extinct in the long term. There are many factors that must be taken into account when creating a management plan for threatened and endangered species and a threatened and endangered status assessment for a species. All of the critical errors in Downer’s misapplication of genetics to the horses of the Salt River aside from the incorrect assumptions about the horses, there are many more critical errors including but not limited to: management objectives, historical biology, habitat, ecology, physiology, past management practices, politics, etc. that must be taken into account in a threatened and endangered status assessment for a species.

In summary, Downer did not provide any data to support or assess the conservation value of the Salt River horses, and therefore he did not provide any data to support or assess a minimum number of horses that would be considered to be genetically viable. In other words, he did not provide any data to support or assess 125 horses as being genetically viable, but he also did not provide any data to support or assess a number of horses less than 125 as being genetically non-viable. Only with a Salt River-specific analysis of genetic data and demographic data can we assess the target number of horses and determine if that number is (1) adequate, (2) marginal, or (3) not viable.

Downer minimises the more immediate limitation: forage capacity

Rather than accurately portraying the existing Salt River horses to be a healthy, sustainable free-roaming population, after the population has been reduced in size, “intensive management” of them would begin. The information on the Salt River horses available on the Internet supports the opposite view of Mr Downer.

The U.S. Forest Service presented information on potential carrying capacity on the Lower Salt River in 2019. One of the methods for estimating forage production on the Lower Salt River was provided by the University of Arizona. Using that information, the University estimated ‘accessible production and allowable use’, which was determined to support a carrying capacity of approximately 20 horses on the Lower Salt River (Dyess, 2019).

Habitat Assessment for Native Plants Along the Lower Salt River. This assessment, conducted by the University of Arizona in April 2025, found the average forage production for native plants along the Lower Salt River to be 54.6 pounds of dry forage per acre of pasture. This amount of forage does not support the current number of horses allowed along the Lower Salt River on natural forage alone. The assessment also found evidence of hedging of several species, including jojoba, mesquite, and wolfberry, along the Lower Salt River. The assessment did find sites that were horse-accessible and sites that were horse-excluded and described those sites in detail. The assessment also described probable negative impacts of continuous grazing by horses on perennial plants along the Lower Salt River during an extreme drought.

Again, the numbers provided in the assessment would not serve as a maximum or even recommended census size for the horses in the Salt River herd. They do, however, disprove a crucial premise of the assessment – that the horses are currently existing naturally healthy and self-sustaining at their current numbers. A managed herd of free-roaming horses, already an intensively managed animal population (supplementally fed, contraception implemented, monitored and managed by humans, individual horses medicated as needed, and pastures fenced), does not need to be reduced in numbers to become a healthy, managed, and self-sustaining animal population. Rather, issues with their current management would need to be addressed and ameliorated in order to ensure the health and welfare of this unique equid population.

“Returned native species” is an advocacy term, not a term with any ecological definition or legitimacy in this context.

Returned native species: Mr Downer (2026) calls the modern free-roaming horses a “returned native species” because the genus Equus evolved originally in North America. Although the genus Equus originally evolved in North America, all native North American equids became extinct at the end of the last Ice Age. Free-roaming horses in the Americas today are descended from domesticated stock introduced to the New World by people, long after the horses originally native to North America had gone extinct (Brischke et al., 2024).

While the genus Equus is native to North America (Downer, 2026), the Equus species currently found as free-roaming feral horses in the Americas are all descendants of introduced domesticated Equus species and thus are considered feral, not native. In addition, the horses were absent from the Americas for thousands of years and were introduced back to the continent at a time when native ecosystems had undergone major changes in climate, plant and animal communities, herb and tree formation, etc.

Distant evolutionary ancestors of today’s horses once roamed this continent. That is not enough to designate free-roaming horses as “returned native species”. Like other introduced species that have long since naturally distributed themselves to wild areas of the world, many are considered to be ‘wild’, but that does not make them members of the native species inventory. They are feral animals, descendants of introduced domestic horses. So while horses of this type may be very special, are very valuable to human culture, and therefore worthy of our protection in a historical, aesthetic, or even humanitarian sense, that is quite different from saying they should be considered members of the native species inventory.

On the other hand, those who appreciate these horses of domesticated ancestry and manage and protect them because of cultural, historical, humanitarian, and aesthetic values need to have a separate policy issue developed and not to be confused with this badly labelled and misguided advocacy term “returned native species”.

The Ecosystem-Benefit Argument Examines Processes But Does Not Examine The Net Ecological Effects Resulting From Them.

A variety of processes take place in an ecosystem occupied by free-roaming horses and other large herbivores such as deer. In the case of horses, seeds are dispersed, nutrients are moved, manure is deposited, and the soil is enriched by their presence. All large herbivores, for example, move nutrients around, deposit manure, and can even act as seed dispersers. However, the presence of these processes does not automatically mean that the net effect of free-roaming horses on the ecosystem is positive.

Does it matter that horses move nutrients, deposit manure, and act as seed dispersers for plants, whether native or non-native? Similar processes occur in large numbers of other large herbivores. The question is whether the presence of free-roaming horses has a net positive or negative effect on ecosystems.

• Which plant species are being dispersed?
• Are they native or invasive?
• How much vegetation is being removed?
• Are plants able to recover?
• Is soil being protected or exposed?
• Are riparian areas being degraded?
• Are native animals being displaced?
• Is grazing pressure compatible with long-term plant productivity?

Seeds of viable plants, including non-native species, can pass through a horse’s digestive system and thus be dispersed (Quinn et al., 2008). In western Colorado, for example, cheatgrass seeds germinated from the faecal samples of horses as well as from those of other domestic and wild species of herbivores. Thus, the seeds of non-native plants are dispersed by a variety of animals and management of invasive species such as cheatgrass should include all animals in an area.

Reviews of scientific research studies and reports dealing with a host of environmental topics affected by the presence of free-roaming horses on rangelands across North America revealed that at excessive numbers, free-roaming horses cause a decrease in plant Community-Type cover and increases in measures of bare ground, soil compaction, erosion potential, destruction of habitats near water sources and increased competitive pressures upon limited water on rangelands. Although author Downer (2026) recognises the potential of very large numbers of free-roaming horses to cause very serious harm to habitats and species, he does not provide any information or calculations regarding what numbers of horses would be considered ‘excessive’ on the Salt River and its associated plant communities.

That information would be crucial in order to determine the extent to which current use of this habitat is in excess of its sustainable use. The presence of other environmental stressors impacting the habitat (i.e. cattle) does not equate to an environmental impact caused by free-roaming horses being insignificant and thus ignored. He agrees that one must compare the impact of horses against other pressures such as livestock grazing, recreation, human development, water diversion, and vehicle use on natural resources (Downer, 2026).

Assessments of environmental impacts most often evaluate the ecological effects of all environmental stresses at a site, including those attributed to animals, humans, water, and plants. Thus, the ecological effects of free-roaming horses should be evaluated within the context of all other environmental stresses at the study site. However, the impacts of the horses do not disappear because other environmental pressures such as cattle grazing, tourism, development, water diversion, and vehicle tracking also impact the Salt River landscape. Thus, Downer is correct to urge an assessment of all the human uses of the Salt River landscape. But each of the various environmental pressures (i.e., horse impacts, livestock grazing, recreation, development, water diversion, vehicle tracking) must be addressed in sound management according to the data or evidence.

The sound management of resources in the face of a variety of environmental stressors involves the management of each stressor as a fact, given such information as: 1) livestock numbers and their season and length of stay; 2) horse numbers and distribution; 3) levels of recreation and vehicle access; 4) water use and management activities

• livestock numbers, timing and duration
• horse numbers and distribution
• recreation and vehicle access
• water management
• development
• drought and climate conditions.

“Nobody should single out the horses” is not a valid response to quantified data that demonstrates the impacts of a measured amount of horse grazing. It is a political ploy that attempts to shift the blame for adverse impacts from non-native livestock to the horses.

The tourism argument is asserted rather than quantified

The Salt River horses have obvious cultural, recreational, photographic and aesthetic value to people visiting this area of Arizona. Many people visit here hoping to see feral horses. Businesses in the surrounding area are supported by “horse lovers” touring the Salt River in search of horses. The Salt River horses unquestionably have cultural, recreational, photographic and aesthetic value and thus draw tourists to the general area where they reside. Potential economic benefits to local businesses from this type of tourism would need a formal economic evaluation and data (from visitor surveys, their expenditures, tax revenue analyses, comparisons with other potential uses, etc.) which Mr Downer does not provide for any number of horses (125, 200 and approximately 275 estimated to currently exist).

The value that people assign to viewing horses in the wild does not necessarily translate to the greatest sustainable economic benefits when as large as possible. In fact, a smaller number of horses could be as visible as the current horses and even more visible under the correct viewing circumstances and with proper visitor management. On the other hand, viewing access to the horses and visitor management could be even better with a smaller number of horses (the focus of all this is to view a symbol of protected wildlife, after all!). In contrast, negatively impacted habitat, horse concentrate browsing, artificially fed horses, conflict with other user groups, and negative impacts to the horses themselves would have a severe, very negative impact upon all of the experiences and conditions that Mr Downer described, which he would obviously be working to protect for future generations.

Mr Downer performed no formal economic analysis of potential tourism with horses of various populations. He acknowledged the horses had value to people visiting the area and that potential existed for tourism with the horses but performed no investigation to compare various populations for potential for greatest sustainable economic benefit.

“Reserve design” lacks analysis for implementation.

Mr Downer suggests that the horses should be allowed to graze in the surrounding Sonoran Desert hills and mountains. This would give them a much larger area of habitat to distribute the grazing pressure in a more natural manner. Increased habitat area would allow the horses to distribute grazing pressure over a larger area than if they were confined to a small area of Salt River bottom land. But Mr Downer needs to have:

• habitat-suitability map
• forage inventory for the proposed expansion
• water-source assessment
• land-ownership or jurisdictional analysis
• native-wildlife conflict assessment
• road-safety analysis
• fencing plan
• legal mechanism
• budget
• projected horse-distribution model
• whether horses would actually move from the river.

Spreading the grazing pressure from current stock numbers across the proposed reserve for threatened species habitat would extend the impacts of horses on native plants and animals to new areas. Rather than a simple spread of impact, the effects of horses on native species would extend to new areas. The stock would also focus on new water sources, creating a concentration point for increased use by stock and increasing impacts and requirements along stock routes, crossing points, and paddock boundaries. Additional fencing and human intervention would also increase in these areas.

Reserve design is a real conservation discipline and should not be used as a euphemism to grant favoured species more space. The discipline of reserve design requires quantified assessments of habitat suitability, clear and quantifiable ecosystem objectives, and a thorough feasibility study.

What is reasonable?

Several general principles in the essay are reasonable:

• A single census number does not in itself determine whether a population is genetically and demographically viable for conservation.
• Genetic, demographic and habitat evidence should be transparent.
• Cultural, recreational and economic values should be considered.
• Management and removals should be humane.
• Population targets should be monitored, and where evidence indicates targets need to change, then management practices also need to change.
• Comparing the impacts of horses to other impacts on the environment.

However, the mentioned principles do not prove that 125 horses would be “genetically compromised” to form a “display population”.

As Mr Downer states in his essay, no single number can establish whether a population is or is not sustainable. Mr Downer failed to provide his readers with pertinent information regarding the genetics and demographics of a reserve population, which is surprising given the preceding information provided in his essay and the principles for the evaluation of equid populations for reserve that he developed (Downer, 2026). The fact that Mr Downer developed principles for evaluating equid populations for reserve lends credence to the fact that he believes reserve design is a legitimate form of conservation, yet he does not use those same principles to support his assertions about 125 horses being genetically compromised as a ‘display population’ of 125 horses.

Conclusion

Mr Downer starts with the preconceived notion that the best management of wild horses would be to allow and even encourage a much larger population of horses than what is currently allowed to exist in the wild. Thus, he selects the portions of the many scientific studies on wild horses that support his views of wild horse management.

He fails to provide a scientifically reasonable conclusion for the size of the stable population in this essay. In other words, 125 horses are either safe or too many for the stable population in this case.

• Treats census size as though it directly determines genetic viability
• Offers no Salt River–specific genetic analysis
• Downplays the data presented on available forage and the fact that the current population size cannot be supported by the habitat
• Treats ancient evolutionary ancestry as proof of modern native status
• Lists potential benefits to animals of including them in measurement of ecosystem services but does not try to determine if there are any positive effects that would result from including wild horses in such measurements
• Invokes tourism without an economic study; and
  proposes habitat expansion without a feasibility assessment.

Final words

A scientifically sound population size goal would need to consider several data points: 1) the amount of forage and water naturally available in the study area and how that could support a current or proposed population size of horses, and the welfare of the horses; 2) the protection of native species and their habitats; 3) the breeding structure among horses in the study area; 4) the effective population size and a plan for long term genetic monitoring; and 5) clear management goals for the study area. Simply relying on personal conviction and images of tourism, as well as the horses’ ancient evolutionary ancestry and use of the term “native”, does not constitute data to be used in place of information addressing these parameters.

Dr Meredith Hudes-Lowder, Biostatistician, DNP
August 5, 2026

References

Beever, E. A., Huntsinger, L., & Petersen, S. L. (2018). Conservation challenges emerging from free-roaming horse management: A vexing social–ecological mismatch. Biological Conservation, 226, 321–328.

A.S. Brischke, E. Greene and J.D. Hennig, Unintended consequences of the Wild Free-Roaming Horses and Burros Act (AZ2099-2024), University of Arizona Cooperative Extension, 2024.

Davies KW, & Boyd CS (2019) Ecological effects of free-roaming horses in North American rangelands. BioScience 69(7): 558–565.

Downer, C. C. (2026). Protecting the Salt River wild horses is an investment in Arizona’s natural heritage and eco-tourism. Trend Report: Tourism and Hospitality, August 2026.

Dyess, J. Estimating capacity for horses in the Lower Salt River area. U.S. Department of Agriculture, Forest Service, Southwestern Region. USDA, Forest Service, Southwestern Region, August 19, 2019. online PDF.

B. Fernald (ed.), Genetics in Conservation. Cambridge: Harvard University Press. pp. 365-391.

S.R.B. King, K.A. Schoenecker and D.J. Manier. Potential spread of cheatgrass (Bromus tectorum) and other invasive species by feral horses (Equus ferus caballus) in western Colorado. Rangeland Ecology & Management, 72, 2019.

Quinn, L. D., Kolipinski, M., Coelho, V. R., Davis, B., Vianney, J.-M., Batjargal, O., Alas, M., & Ghosh, S. (2008). Germination of invasive plant seeds after digestion by horses in California. Natural Areas Journal, 28(4), 356–362.

University of Arizona Cooperative Extension. ( 2025). Vegetation assessment in the Salt River Horse Management Area, April 2025. Gila County Cooperative Extension.