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: 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.

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

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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.

Do Wild Horses Reduce Wildfire Risk? An Assessment of the Scientific Evidence

One of the most widely promoted arguments for keeping or expanding wild horse populations is that they reduce wildfire risk. A concept presently gaining popularity in its application to wild horses for wildfire mitigation on public lands is that proposed by Captain William E. Simpson II (Simpson, n.d.), a retired U.S. Merchant Marine and commercial airline pilot who resides on the California–Oregon border. Simpson has years of observation of a free-roaming band of wild horses that reside on his property and has developed a proposal called the ‘Wild Horse Fire Brigade‘ (Simpson, n.d.). Simpson’s fire-controlling concept lacks academic research backing in fields such as ecology, wildlife management, rangeland ecology and management, silviculture and fire ecology. Even though an interesting concept, it lacks substantial data from replicated studies that have been subject to peer review, published in credible scientific journals, and applicable in the North American context (O’Neill, 2022).

While transferring thousands of wild horses from BLM holding facilities to spread across wildland fires on remote Federal Forests and Wilderness Areas for year-round grazing on the very fuels that the horses are to consume to reduce future wildland fires on public and private lands. This idea may garner the attention of the public and the enthusiasm of wild horse advocates as a management hypothesis; there is no study or data that support the use of free-roaming feral horses for the purpose of reducing the frequency and total area burned of individual wildfires, as well as the costs of fire suppression in North America.

In evaluating evidence for the role of wild horses in reducing fuels and fire, the great majority of scientific work has focused on horses in managed grazing systems (as contrasted with unmanaged feral horses) across a variety of Mediterranean ecosystems. These studies find that, under certain conditions and with management of key factors such as stocking rate, horses can reduce grass height and, on the ground surface, consume fine fuels. But they also find that horses have relatively little impact on woody plants of any kind and that the effect of horses in reducing fuels to reduce fire is site-specific, depending greatly on the intensity of horse grazing and the number of horses present on the ground. Finally, these studies of horses in Mediterranean-type ecosystems with managed grazing note that, in no case, do horses alone provide sufficient fuel reduction to mitigate wildfire. Horses must be part of a combination of grazing animals, including cattle and browsers, along with prescribed fire and mechanical fuel treatment (Rigueiro-Rodríguez et al. 2012; Janeiro-Otero et al. 2024; Ribeiro et al. 2025; Gort-Esteve et al. 2025).

In studies in Mediterranean regions, such as Galicia and Portugal, horses of all categories (feral, semi-domesticated and domestic) are managed as part of a landscape, within fenced areas such as gorse heathland with scrub and grasses. In contrast, fuels in wildland fires in western North America consist mainly of drought-stressed shrubs and trees such as sagebrush, pinyon-juniper, and other woody species, as well as perennial and annual grasses, including cheatgrass, and many other fuel types. Such large, long-duration wildland fires are influenced by a complex array of factors, including drought, wind, the persistence of continuous fuels, topography, and weather over extended periods. Such fires cannot be managed by a single variable, such as wild horses grazing.

The largest fires in recent years have burned in the very same HMAs where wild horses reside. After the 285,000-acre 2015 Soda Fire burned the entire Hardtrigger and Sand Wash Basin HMAs and portions of the Black Mountain HMA, BLM staff spent months gathering wild horses from the Hardtrigger HMA to manage them in holding facilities for emergencies, as the forage in that huge area had been burned to the ground. In 2024, the Jump Fire burned much of the Sands Basin and Four Mile HMAs, and an emergency gather was conducted for the thousands of wild horses dispersed across those burned areas to reestablish a stable, healthy wild horse population with suitable forage. Similarly, after the 2012 Jakes Fire burned a huge section of the Snowstorm Mountain and Little Humboldt HMAs, the wild horses from those HMAs were managed from the holding facilities for several years as the forage that existed in that area was severely reduced and burned to the ground, and it took many years to reestablish. This same management has occurred following other major fires in the Fox and Lake Range, Three Fingers, and Centennial HMAs.

In addition, the use of the Salt River horses in Arizona as an example of wild horses performing natural fire control has been debunked by fires within the horses’ home range and beyond that required fire suppression by agencies. Examples of these fires include the 2017 Cactus Fire, the 2020 Dome Fire, the 2020 Christmas Fire, and the 2024 SR-87 Fire.

While horses do impact the landscape and specific fuels within it, the extent to which they might affect potential wildfire and resulting behaviour is typically localised. The extent of that impact would be significantly influenced by various management factors, including the availability of forage for the horses.

In summary, there is no scientific basis to support the use of free-roaming feral horses as a meaningful component of the landscape for mitigating wildfire. Additional well-designed studies are needed to determine specific reductions in fuel use, resulting changes in fire behaviour, and subsequent impacts on the number and size of individual wildfires in climates, environments, and ecologies similar to those of the American West. Until such time, the Wild Horse Fire Brigade remains an untested fire management hypothesis.

References

Bureau of Land Management. (2015). Soda Fire Wild Horse Gather.

Bureau of Land Management. (2016). Three Fingers Emergency Wild Horse Gather.

Bureau of Land Management. (2020). Centennial Herd Management Area Gather.

Bureau of Land Management. (2023). Fox and Lake Range Emergency Wild Horse Gather.

Bureau of Land Management. (2024). Sands Basin and Four Mile Emergency Wild Horse Gather.

Bureau of Land Management. (2026). Jakes Fire Emergency Wild Horse Gather.

Gort-Esteve, A., Bartolomé Filella, J., Roselló Molinero, X., Torra Burgués, A., Riera, J. L., & Nieto-Espinet, A. (2025). Dietary strategies of feral and domestic horses under varying grazing pressures: Insights for Mediterranean forest management. Agroforestry Systems, 99, 208.

Janeiro-Otero, A., Álvarez, X., & Dormann, C. F. (2024). Application of remote sensing to understand the role of Galician feral horses in the biomass reduction of a shrub-grassland-dominated landscape. BMC Ecology and Evolution, 24, 89.

O’Neill, S. (2022, October 23). Meet the man who says wild horses could help prevent the next wildfire. NPR.

Ribeiro, I., Aliácar, S., Domingos, T., McCracken, D., & Proença, V. (2025). Semi-wild horse grazing as a rewilding strategy: Assessing effects on vegetation structure and composition in the Côa Valley, Portugal. Frontiers in Ecology and Evolution, 13, 1596560.

Rigueiro-Rodríguez, A., Mouhbi, R., Santiago-Freijanes, J. J., González-Hernández, M. P., & Mosquera-Losada, M. R. (2012). Horse grazing systems: Understory biomass and plant biodiversity of a Pinus radiata stand. Scientia Agricola, 69(1), 38–46.

Simpson, W. E., II. (n.d.). Wild Horse Fire Brigade advocacy materials.

Introduction

In recent years, the question of whether horses persisted in North America throughout the Holocene, rather than going extinct at the end of the Pleistocene and being reintroduced by Europeans, has gained traction in some advocacy and public history circles. This idea was articulated in the 2017 doctoral dissertation by Dr Yvette Running Horse Collin, which argued that horses should be considered continuously native to the Americas. That dissertation and related claims circulated widely on social media and cultural blogs, prompting detailed public criticism.

One such response is the 2019 analysis on A Hot Cup of Joe titled “Pseudoarchaeological claims of horses in the Americas,” which systematically examines the evidentiary basis of post-Pleistocene survival claims and highlights methodological problems in the sources and interpretations used to support them (Feagans, 2019, https://ahotcupofjoe.net/2019/07/pseudoarchaeological-claims-of-horses-in-the-americas/). While that blog post effectively identifies many problematic assertions, it does so within the broader genre of public archaeology commentary. A comprehensive scientific evaluation requires engagement with the full body of archaeological, paleontological, radiometric, and genomic evidence, assessed according to standard disciplinary criteria.

The following analysis synthesises key lines of evidence, radiocarbon chronology, stratigraphic control, paleogenomic continuity, extinction modelling, and species distribution data to evaluate the continuous-Holocene survival hypothesis on strictly scientific grounds. It situates the public critique represented by A Hot Cup of Joe within a more formal framework of empirical support and methodological rigour, clarifying why the mainstream extinction-and-reintroduction model remains the most parsimonious explanation in the current scientific record.

The hypothesis that horses survived continuously in North America throughout the Holocene, as proposed in the 2017 dissertation by Dr Yvette Running Horse Collin, warrants evaluation according to established standards in Quaternary palaeontology, archaeology, radiocarbon chronology, and paleogenomics. Although the evolutionary origin of the genus Equus in North America is well documented, the central issue concerns the continuity of ecological conditions across the terminal Pleistocene boundary. Current scientific evidence convincingly supports a Late Pleistocene extinction of North American horses, followed by the 16th-century reintroduction of domesticated Eurasian lineages.

1. Radiocarbon Chronology and the Extinction Boundary

The North American Equus fossil record is extensive and geographically widespread during the Late Pleistocene. Thousands of specimens have been identified, with radiocarbon dates clustering between approximately 10,000 and 11,000 years before present (BP), which coincides with the terminal Pleistocene megafaunal extinction event (Faith & Surovell, 2009; Guthrie, 2006). After this extinction boundary, securely dated horse remains are consistently absent until the historic period.

Large-scale faunal occurrence databases, such as FAUNMAP II, which compile stratigraphically vetted mammalian records across North America, demonstrate a pattern of terminal Pleistocene disappearance for Equus without documented Holocene continuity (Graham & Lundelius, 2010). The extinction boundary for Equus is temporally aligned with other megafaunal losses, including mammoths and mastodons, and corresponds with wider ecological restructuring at the end of the last glacial period (Lorenzen et al., 2011).

To overturn this extinction model, one would require:

1. Securely stratified Holocene Equus remains

2. Direct radiocarbon dates on uncontaminated collagen

3. Replication across independent sites

To date, no reproducible dataset that meets these criteria has been published in the peer-reviewed literature.

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2. Stratigraphic Standards and Archaeological Control

In Quaternary archaeology, contextual integrity is fundamental. Surface finds, redeposited material, or specimens lacking documented excavation records cannot establish species continuity. Claims of Holocene survival that rely on:

* Uncontrolled provenience

* Mixed sediment layers

* Artefact association without direct dating

do not meet accepted archaeological standards. The presence of a single intrusive specimen in a disturbed context cannot overturn a continent-wide extinction pattern supported by evidence from hundreds of stratified sites.

If Holocene horses had persisted at ecologically meaningful population sizes, we would expect:

* Hunting assemblages

* Butchery marks

* Distributed osteological remains across occupation layers

Such material evidence has not been identified in securely dated Holocene archaeological contexts to date.

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3. Paleogenomic Evidence and Lineage Discontinuity

Ancient DNA analysis delivers an independent line of evidence. Sequencing of Middle and Late Pleistocene North American horses reveals distinct lineages that disappear from the record at the end of the Pleistocene (Orlando et al., 2013). Subsequent genomic analyses confirm that modern horses derive from domesticated Eurasian populations rather than from surviving endemic North American Pleistocene stock (Orlando, 2020; Bailey & Brooks, 2013).

Importantly, no ancient Holocene North American Equus specimen has yielded genomic data demonstrating continuity with pre-extinction lineages. In extinction biology, the combination of lineage discontinuity and stratigraphic absence strongly supports true extinction rather than a demographic bottleneck.

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4. Extinction Modeling and Ecological Parsimony

Late Pleistocene megafaunal extinctions are widely attributed to interacting pressures, including climatic warming, vegetational shifts, and human expansion (Barnosky et al., 2004; Lorenzen et al., 2011). Regardless of whether anthropogenic overkill, climate forcing, or synergistic mechanisms predominated, the extinction of Equus is consistent with a wider continental extinction event that affected multiple taxa simultaneously.

From a population ecology standpoint, a continent-wide species persisting undetected for 10,000 years would require:

* Viable breeding populations

* Stable habitat occupancy

* Sufficient demographic size to avoid genetic collapse

Such persistence would be expected to produce a detectable osteological and genetic signature. The absence of this evidence argues against the survival of Equus in the Holocene.

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5. Iconography and Effigy Claims

Rock art, figurines, and symbolic representations cannot independently establish species survival. Quadrupedal depictions are often morphologically ambiguous, and direct dating of petroglyphs presents methodological challenges. Even if such imagery were conclusive, cultural representation does not demonstrate biological continuity. Archaeological science requires physical, datable remains to confirm the presence of taxa.

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6. Oral Traditions and Evidentiary Categories

Oral traditions possess cultural authority and historical meaning. However, scientific reconstruction of species chronology relies on a distinct evidentiary framework. In the absence of corroborating physical remains, oral accounts cannot substitute for radiometrically dated material evidence. This distinction is methodological instead of a reflection of cultural value.

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7. Evolutionary Origin vs. Ecological Nativeness

Horses originated in North America millions of years ago and subsequently dispersed into Eurasia (MacFadden, 1992). This evolutionary origin is undisputed. However, ecological nativeness is defined by uninterrupted historical presence within a timeframe relevant to management and conservation science.

A species that becomes extinct and is later reintroduced, regardless of its ancient ancestry, does not meet the criteria for continuous ecological nativeness under standard biological frameworks.

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Conclusion

The continuous-Holocene survival hypothesis currently lacks:

* Securely dated Holocene Equus remains

* Demonstrated genetic continuity

* Stratigraphically controlled archaeological evidence linking the extinction boundary

In contrast, the extinction-and-reintroduction model is supported by radiocarbon chronology, paleogenomic analysis, faunal distribution databases, and extinction ecology theory. Unless reproducible, directly dated Holocene specimens are produced and independently validated, the terminal Pleistocene extinction of North American horses remains the most scientifically robust explanation.

Dr Meredith Hudes-Lowder ©2026

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References

Bailey, E., & Brooks, S. A. (2013). Horse genetics (2nd ed.). CABI.

Barnosky, A. D., Koch, P. L., Feranec, R. S., Wing, S. L., & Shabel, A. B. (2004). Assessing the causes of Late Pleistocene extinctions on the continents. Science, 306(5693), 70–75. https://doi.org/10.1126/science.1101476

Faith, J. T., & Surovell, T. A. (2009). Synchronous extinction of North America’s Pleistocene mammals. Proceedings of the National Academy of Sciences, 106(49), 20641–20645. https://doi.org/10.1073/pnas.0908153106

Graham, R. W., & Lundelius, E. L., Jr. (2010). FAUNMAP II: New data for North America with a temporal extension for the Blancan, Irvingtonian and early Rancholabrean (FAUNMAP II Database, Version 1.0) [Data set]. University of California Museum of Paleontology.

Guthrie, R. D. (2006). New carbon dates link climatic change with human colonization and Pleistocene extinctions. Nature, 441, 207–209. https://doi.org/10.1038/nature04604

Lorenzen, E. D., et al. (2011). Species-specific responses of Late Quaternary megafauna to climate and humans. Nature, 479, 359–364. https://doi.org/10.1038/nature10574

MacFadden, B. J. (1992). Fossil horses: Systematics, paleobiology, and evolution of the family Equidae. Cambridge University Press.

Orlando, L., et al. (2013). Recalibrating Equus evolution using the genome sequence of an early Middle Pleistocene horse. Nature, 499, 74–78. https://doi.org/10.1038/nature12323

Orlando, L. (2020). The evolutionary and historical foundation of the modern horse: Lessons from ancient genomics. Annual Review of Genetics, 54, 563–581. https://doi.org/10.1146/annurev-genet-021920-011805

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Presented below is a blog post in its entirety by Carl Feagans, an archaeologist who refutes Dr Yvette Running Horse Collin’s dissertation claims.

The blog post is located here: https://ahotcupofjoe.net/2019/07/pseudoarchaeological-claims-of-horses-in-the-americas/

“Pseudoarchaeological claims of Horses in the Americas“

July 16, 2019 Carl Feagans Archaeology 32

“Pseudoarchaeological claims of horses present in the Americas isn’t all that new. Recently, however, a new story started making the rounds on Facebook with a slightly different twist. Instead of trying to prove the introduction of the horse by the “lost tribe of Israel” or “the Philistines” as they settled the Americas a few thousand years ago, this story introduces something more plausible. Contrary to the current scientific consensus, horses, so the claim goes, didn’t go extinct in the Pleistocene and were not re-introduced post-contact. There are a lot of horse-lovers out there that get angry at people, like some cattle ranchers, who consider wild horses to be invasive species and want herds destroyed rather than compete with their cattle on public grazing lands. So I expect this fuels some of this claim.

The claim itself isn’t necessarily crazy. I find the general notion that one or more species of Equus might have survived the Pleistocene to be an interesting scientific question. But that’s not the way Yvette Collin seems to approach the issue. In fact, her PhD dissertation (Collin, 2017) from the University of Alaska Fairbanks takes a decidedly pseudoscientific approach to addressing it.

In her dissertation, Collin’s stated purpose is to “deconstruct the history of the horse in the Americas and its relationship with the Indigenous Peoples.” She seems to begin with a conclusion—that there is a “Western science” seeking to “disregard, purposefully exclude, and reconfigure” the traditional knowledge of Native Americans. Ultimately, she’d like to “reconstruct the history of the horse in the Americas in a way that is unbiased and accurate.”

Toward this endeavor, she fails.

Let’s begin with the literature review

Collin seems to miss the point of the literature review. She describes non-written forms of information transmission by Native Americans (oral tradition, wampum belts, rituals, etc.) then goes on about how Natives were persecuted and oppressed until 1978 when Carter signed the Freedom of Religion act, etc.

She mentions how historians record the introduction of horses to the Indians in the 1690s but there are Spanish records that document Indians using horses as early as 1521 in Georgia and the Carolinas. It turns out she’s citing Richard Thornton who is citing Pietro Martire (Peter Martyr) d’ Anghiera’s De Orbo Novo [The New World] (Martyr D’ Anghiera, 1912)?, written in 1530.

One immediately wonders why she didn’t cite the original source. If she had, she might’ve noticed that Thornton, a pseudoarchaeologist, tells it like he wants it known. While Thornton mentions that one of Martyr’s key informants, a captured Native American named Francisco Chicorana, could “not confirm or deny the presence of horses,” he fails to mention that Martyr also wrote of the Americas having lions and tigers and a strange elephant-like beast that we would later understand be a tapir. While it would be easy to conflate a jaguar or puma with a lion or tiger seeing one for the first time, Martyr’s mentions of the horse and Chicorana’s inability to confirm or deny their presence in Duhare (modern Geogia/Carolinas area) isn’t as Thornton misleads one to believe. Martyr writes:

In place of horses, the king is carried on the shoulders of strong young men, who run with him to the different places he wishes to visit. At this point, I must confess, that the different accounts cause me to hesitate. The Dean and Ayllon do not agree ; for what one asserts concerning these young men acting as horses, the other denies. The Dean said: “I have never spoken to anybody who has seen these horses,” to which Ayllon answered, “I have heard it told by many people,” while Francisco Chicorana, although he was present, was unable to settle this dispute. Could I act as arbitrator, I would say that, according to the investigations I have made, these people were too barbarous and uncivilised to have horses.

Collin quotes Martyr directly only to include that last line which denigrates the Native American as inferior to the white Europeans.

To further explain why a proper literature review wasn’t possible, she goes on to describe how Native oral traditions are “precise” and “convey depth and detail in a way that modern-day languages and records are unable” (Collin, 2017, p.30). Collin points out that Native American languages often have many words for concepts like rain, snow, wind, etc., implying that this is what maintains fidelity of a concept being transmitted from one generation to the next.

She omits any agenda by individuals or groups to propagandize, elaborate, embellish or change stories to keep them relevant—all present in human cultures throughout the globe in both historic and prehistoric (i.e. pre-written) periods. Though Collin does provide many 16th century accounts of early visitors to the New World recording and documenting the horses that they spotted. How do we determine which of these are accounts of horses lost by previous expeditions (escaped after being brought off ship or from ships that sunk hitting reefs or rocks) and which of these are partial or pure embellishment meant to entice European benefactors into funding additional expeditions? The horse, after all, was a resource.

What she noticeably omits in this literature review are biological, paleontological, and genetic sources of information. If one has a hypothesis regarding the existence of a mammalian species, one expects these in the literature review. No doubt Collin would have us believe that Native American oral tradition is trustworthy because cultural tradition and linguistic style was guaranteed to ensure fidelity and preclude embellishment or omission of facts inconvenient to the narrative.

Physical evidence

So what physical evidence does Collin present? Within the literature review section of her dissertation, Collin describes a 3-inch clay horse figurine that was “found on Roods Creek about 2 miles from the Chattahoochee River.” Collin also describes a small stone horse effigy that “was found in a 1974 dig ‘near the Yuchi Creek near Fort Benning, Georgia.’”

As physical evidence goes, these items are pretty much useless. First, the source she’s citing is a pseudoarchaeological book on pre-Columbian visits to the Americas by white Europeans (Farley, 1993)?. Moreover, neither of these objects are with any context that can be dated or effectively described. The first was alleged to be found by a Catholic friar; the second was by a pair of boys digging in the bank of a creek (Farley, p. 342) (Collin, p. 47).

Read Collins’ account carefully:

…and that “Manford Metcalf of Columbus, Georgia, put into my hand a small stone effigy which resembled a horse head,” which was found in a 1974 dig “near the Yuchi Creek near Fort Benning, Georgia.”

And now Farley’s original passage:

At the same 1979 symposium, Manford Metcalf of Columbus, Georgia, put into my hand a small stone effigy which resembled a horse head. He explained that his boys had found it in 1974 while digging in the side of a hill near the Yuchi Creek near Fort Benning, Georgia.”

As an archaeologist, I can tell you there’s a definite distinction between “a 1974 dig” and “boys digging in the side of a hill in 1974.” This is a blatant mischaracterization—a borderline lie—by Collins.

Rock art and geoglyphs

Collin is correct when she says rock art motifs with a horse are considered as post-contact period motifs. But it isn’t because of a “dominant Western culture” or a refusal to date the rock art in other ways. It’s because this is an effective method of dating: use of motifs. Dating rock art is hard. Not just complicated or involved hard, but really hard. Sometimes it just cannot be done. The most effective methods are relative association of a motif or stylistic element with an event or period. Often the best dates that can be had are large ranges. Occasionally, a fairly well dated element will be of a pigment that overlaps or underlays another pigment in a consistent fashion, allowing the archaeologist recording the rock art to make some basic, relative assumptions about the dates.

While it is possible to do radiocarbon analysis on rock art, it’s an extremely involved and destructive process. Pigment has to be scraped from the rock art itself. Usually, the archaeologist looks for a recent spall for a sample candidate. Then the pigment has to be separated. There’s often a binder and an emulsifier along with the pigment material itself. If the archaeologist is very lucky, she’ll have sufficient quantities of one of these elements that happens to be from a formerly living organism and will, thus, have carbon 14 isotopes within it to test.

Very often, however, no viable sample is found and no one wants to go chipping away at the rock art willy-nilly. And, then, when a sample is successfully analyzed, there’s a crazy chance of error. But this is pigment-based rock art. Petroglyphs are a whole other problem. There really isn’t any effective way to date these. It’s possible to date the patina or lichens that begin to build up in the underlying strata after the cortex of the rock is removed by pecking. But this is a pretty rare thing.

One of the ways a patina can form is through a natural process of desert varnish, which is essentially the result of a bacteria that consume manganese and iron dust. Desert varnish (DV) takes thousands of years to form, but it is possible to measure the amount of minerals (Mn, Fe, and Pb) in a petroglyph that is slowly developing that patina of desert varnish again. Using a handheld, x-ray fluorescence device one can measure the pecked portion and the unpecked portions of rock, do some math, then look the age up on a calibration curve. The downside is that the technique is still a bit experimental and requires that the minerals above be present in the natural geology of the area.

One of the rock art examples that Collin cites is from 48th Unnamed Cave in Eastern Tennessee and dates to about 6000 years BP. Captions of the image simply say, “quadruped animal,” but she assumes this is a horse. A direct date was obtained using accelerated mass spectrometry (AMS) on a sample of charcoal pigment. But the date says nothing about the species of the animal. Visually, it’s a quadruped. Instead of citing the primary source (Simek, Cressler, Herrmann, & Sherwood, 2013)? directly, Collin curiously cites an internet news source (Smith, 2013)? and criticizes that writer’s characterization of cave art in the region of East Tennessee as including “otherworldly characters, supernatural serpents and dogs…” by saying “this interpretation of the pictographs illustrating large quadrupeds accompanying people makes little sense culturally,” as if she knew what people 6000 years ago were thinking.

Had she looked at the original source, Collin would have read that the inclusion of canids (dogs, wolves, coyotes) in the local cave art was far from uncommon. And she would have seen an image that was clearly of a group of canines as example. But this might not be her actual complaint since she also says, “no dogs near the dimensional size illustrated in these pictographs were known to exist…” Collin is clearly under the mistaken belief that rock art will only include imagery that is to scale.

Another rock art example Collin uses as evidence that horses were in the Americas in pre-contact times is a pictograph element at Alto de Pitis in Peru. The description (van Hoek, 2013)? as a horse with rider dating to after 1540 is refuted by Collin based on a blog post from NephiCode.com (DowDell, 2016)?, which she agrees with. She derides van Hoek for not bothering to date the rock art without bothering to describe what dating method would possibly be appropriate for this panel. I honestly don’t know if Alto de Pitris would be a good candidate for XRF dating or not, but van Hoek did, indeed, date this element of the panel, but with relative dating based on the understood existence of the horse in Peru.

Also, among the physical evidence Collin presents for pre-contact horses are the Blythe Intaglios, a set of geoglyphs near Blythe, California in the Colorado Desert. Two of these are of quadrupeds that are generally accepted to be mountain lions. They certainly don’t resemble horses other than being quadruped. While the Blythe Intaglios are often said to be at least 1,000 years old, their actual date is unknown, mainly due to the “lack of associated time-sensitive artifacts and charcoal-bearing features” (Gilreath, 2007 p. 289).

With the geoglyphs, Collin also leans on the words of Craig Downer, who advocates for wild horses and burros to not be seen as invasive. Reviewing his bibliography for the work Collin cited, we see the familiar pattern of going to pseudoscientific sources like the magazine Ancient American—another entity, like NephiCode, with an agenda for arguing that Mormons and Jews were the ancestors of Native Americans.

Downer writes of his own discovery of alleged horse petroglyphs that he personally dated to over 1,000 years old. The method of dating? He visually compared the patina hues (Downer, 2014)?. No XRF device. No long-term study of patination and the associated color hues and patterns. No indication at all of what comprised the patina. So it is not at all surprising, Downer’s article was published in the American Journal of Life Sciences, which is listed on Beal’s List of Predatory Journals (http://bealslist.weebly.com).

Skeletal Remains

Collin continues citing fringe and pseudoarchaeological sources in her PhD dissertation to the point that it just becomes hard to trust any of her sources. There’s a variety of post-contact Equus remains that she describes and the occasional discovery that is alleged to be pre-contact. Such as the Pratt Cave excavations by Ernie Lundelius. Collin now cites another fringe writer (S. E. Jones, 2012)? who spoke of Pratt Cave, where two horse bones were recovered (a metapodial and a portion of a phalanx), both on the surface of the cave interior.

Radiocarbon dating of samples at strata below the surface revealed the oldest date in the cave to be 2820 +/- 180 years BP (Lundelius, E. L., 1979)?. That didn’t keep Jones from stating that there was a date range of 6020 to 5890 BCE for bones deposited on the surface after the samples below that dated to a maximum of about 870 BCE! Ludelius states in his paper on Pratt Cave that the surface bones were from a “small form about the size of an ass” and, although he couldn’t be sure if it was domestic or feral, it was certainly modern and likely introduced to the cave by a predator. It would seem that Jones is pulling data from thin air since he offers no citation that explains the extreme age he claims. Lundelius certainly didn’t use that age and confirmed as much in personal correspondence with me.

Not without a single surprise, Jones’ article was published first in Ancient American magazine a fringe, hyper-diffusionist periodical that features many articles about how ancient peoples in the Americas had contact and help from smarter, more technologically advanced, white people from places like Europe well before Columbus arrived. Collin also cites another set of excavated horse bones that Jones also discussed in that same article. In doing so, she cites the original publication directly but leaves out a critical observation that points to their conclusion: cut marks on the bone from a steel tool. Eckles and his colleagues acknowledge that bone occasionally produces young results (this is because of younger material clinging to buried bone) but agree that the upper limit of their obtained radiocarbon dates (after the mid 17th century) is realistic and that this is an early historic site in Wyoming (Eckles, Lockewood, Kumar, Wedel, & Walker, 1994)?.

Conclusion

Collin begins her dissertation with a clear chip on her shoulder for so-called “mainstream academia” and “Western science.” There is no “western” science. There is science. The methods of which work regardless of where you are geographically or what your ethnicity is. That’s the wonderful and marvelous thing about science is that it can be wielded by even the most oppressed or marginalized among us if its methods are adhered to. The only real trick is to observe the universe in a logical fashion and record data in a manner reasoned enough that it will provide consistent results.

While Collin rightfully pointed out the presence of bias among non-indigenous or non-Native researchers, she also pledged to overcome any bias of her own. She failed. From the outset. Her abstract revealed a conclusion that she began with and proclaimed the data she would find. No serious attempt was shown in her work to falsify her hypothesis, indeed, her null hypothesis was unclear: what would show her to be wrong as she gathered data?

The importance of having indigenous researchers and scientists around the world answering questions and exploring the heritage of their own people cannot be overstated. This is all the more reason why such an endeavor should be undertaken in a manner that places the work in a position that is as close to being beyond reproach as possible. Indeed, this should be a goal of any legitimate research endeavor.

Reliance on sources so questionable as to be considered pseudoscientific, pseudoarchaeological, and pseudohistoric, however, has the effect of diminishing any research endeavor to the fringes of science at best. It places doubt on any future work the researcher produces. And it taints the reputations of those that academically validate it. But more importantly, when it comes to advancing indigenous or historically marginalized people, such works become obstacles to those that deserve that advancement.

Collin’s dissertation cites Ancient Origins, Richard Thornton, and Dell Dowdell, and each of these sources variously or indirectly promote ideas about Native Americans which can be considered racist. Dowdell, the creator of nephicode.com, actively promotes the notion that Native Americans are the descendants of white Mormons and he believes the Earth is only as old as one of the cave paintings mentioned earlier in this article. Conspiracy theorist Richard Thornton publishes pseudoarchaeological claims of Maya settlements in Georgia. And Ancient Origins is a website that traffics in all manner of fake, fraudulent, and fantastic archaeological news, books, and media for profit. Authors they promote range from racists to general conspiracy theorists.

Coming across any one of these in a dissertation for a PhD should be enough to put all that dissertation’s sources in question. There were, perhaps, a dozen or more questionable sources of this caliber.

I’m certainly not categorically opposed to the idea that Equus may have survived the Pleistocene extinction and continues even today. This, I think is a perfectly valid, scientific hypothesis. But it’s one that should be tested using science. Not “Western science.” Not through the lens of non-indigenous academia. It should simply be tested with science, a set of methods available to anyone willing to use them regardless of geographic origin, cultural affiliation, or ethnic heritage.”

References and Further Reading

https://newsmaven.io/indiancountrytoday/news/yes-world-there-were-horses-in-native-culture-before-the-settlers-came-JGqPrqLmZk-3ka-IBqNWiQ

Collin, Y. R. H. (2017). The Relationship Between the Indigenous Peoples of the Americas and the Horse: Deconstructing a Eurocentric Myth (University of Alaska Fairbanks). Retrieved from https://search.proquest.com/docview/1895090520?accountid=6180%5Cnhttp://dw2zn6fm9z.search.serialssolution.com?ctx_ver=Z39.88-2004&ctx_enc=info:ofi/enc:UTF-8&rfr_id=info:sid/ProQuest+Dissertations+%26+Theses+Global&rft_val_fmt=info:ofi/fmt:kev:mtx:disserta

DowDell, D. (2016). The Horseman of Alto de Pitis – Part III. Retrieved from NephiCode.com website: http://nephicode.blogspot.com/2016/05/the-horseman-of-alto-de-pitis-part-iii.html

Downer, C. C. (2014). The Horse and Burro as Positively Contributing Returned Natives in North America. American Journal of Life Sciences, 2(1), 5. https://doi.org/10.11648/j.ajls.20140201.12

Eckles, D., Lockewood, J., Kumar, R., Wedel, D., & Walker, D. N. (1994). An Early Historic Period Horse Skeleton from Southwestern Wyoming. The Wyoming Archaeologist, 38(3–4), 55–68.

Farley, G. (1993). In Plain Sight: Old World Records in Anceint America. Columbus, GA: ISAC Press.

Gilreath, A. J. (2007). California Prehistory: Rock Art in the Golden State. In T. L. Jones & K. A. Klar (Eds.), Colonization, Culture, and Complexity (pp. 273–290). Lanham, MD: Rowman Altamira.

Jones, S. E. (2012, January). Were There Horses in the Americas Before Columbus? Ancient American, 5–6.

Lundelius, E. L., J. (1979). Post-Pleistocene mammals from Pratt Cave and their environmentalsignificance. In H. H. Genoways & R. J. Baker (Eds.), Biological Investigations in the Guadalupe Mountains, National Park, Texas (pp. 239–258). Washington D. C.: National Park Service, Proc.

Martyr D’ Anghiera, P. (1912). De Orbe Novo (F. (trans. . MacNutt, Ed.). Project Gutenberg reproduction ed.

Simek, J. F., Cressler, A., Herrmann, N. P., & Sherwood, S. C. (2013). Sacred landscapes of the south-eastern USA: Prehistoric rock and cave art in Tennessee. Antiquity, 87(336), 430–446. https://doi.org/10.1017/S0003598X00049048

Smith, M. (2013). Ancient Tennessee Cave Paintings Show Deep Thinking by Natives. CNN Online, June 23(Sunday). Retrieved from https://www.cnn.com/2013/06/20/us/tennessee-cave-art

van Hoek, M. (2013). The Horseman of Alto de Pitis, Peru: A Post-Columbian Outsider in a Pre-Columbian Landscape. Retrieved from https://www.academia.edu/22684628/VAN_HOEK_M._2013._The_Horseman_of_Alto_de_Pitis_Peru_A_Post-Columbian_Outsider_in_a_Pre-Columbian_Landscape._Andean_Rock_Art_Papers_-_Part_1_-_Paper_1

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A foal disappeared recently at the Salt River. There are many theories as to the cause of presumed death on line, including a mountain lion attack, posited by the Salt River Wild Horse Management Group. Despite exhaustive searches, the foal could not be found, suggesting scavenger activity. The following presents the causes of foal mortality in free-roaming horses. Given the overpopulation of the horses, reduced resources, and photographs and first-hand accounts of stallions harassing mares/foals at the river and behind the SRWHMG compound, it is possible the foal died from stallion aggression. Infanticide in wild equids, though relatively rare, is a reproductive strategy rather than an act of aggression without purpose. When a foal is killed, the mare often returns to estrus sooner than she would have if she were nursing. Normally, lactational anestrus, the period when a mare does not cycle while nursing, suppresses ovulation through elevated prolactin and reduced gonadotropin (FSH and LH) levels. Once the foal is lost, these hormonal constraints diminish, and the mare can enter estrus within days to weeks, allowing the infanticidal stallion or another bachelor a mating opportunity that would otherwise have been delayed for months.

The death rate of foals in free-roaming horse populations depends on multiple factors, which include seasonal predator attacks, population density, and fertility management systems. The most noticeable natural cause of death in free-roaming horses occurs through cougar (Puma concolor) attacks. Yet, demographic pressure from excessive population density, food scarcity, and birth control side effects leads to social changes that increase foal mortality rates.

Seasonal Cougar Predation and Sex-Specific Hunting Patterns

The MPWHT located at the California–Nevada border shows that cougars kill 70% of their foal victims before they reach three months of age, while half of all foal deaths happen before July starts. The predator did not target any adult horses during its attacks. The predation period occurred between May and June, which coincided with foal birth, while mule deer became the primary prey during the winter months (Turner JW Jr et al., 1992).

Research on kill sites showed that female cougars who had dependent kittens chose to hunt foals during this specific time, while male cougars occasionally killed adult or subadult horses but mainly focused on foals when they were abundant (Andreasen AM et al., 2021). The study in Alberta showed that female cougars primarily hunted newborns, whereas male cougars killed only adult horses in their nine recorded prey encounters (Knopff KH et al., 2010). According to the Salt River Wild Horse Management Group, a few foals have been attacked/killed by mountain lions. https://www.facebook.com/profile/100064860303576/search/?q=mountain%20lion

The same patterns of predator-prey interactions have been documented in Argentina since pumas returned to their natural habitat. The Ernesto Tornquist Provincial Park shows that 74% of foal deaths occurred during spring through summer, while 54% of the deaths involved foals under six months old and 53% showed evidence of puma predation (Bostal F et al., 2025).

The combination of excessive population numbers with insufficient food resources makes foals more vulnerable to predators.

Behind the SRWHMG’s property along the Bee-Line Highway, horses gather for food (hay and alfalfa) and water. There can be as many as 100+ horses on any given day, several of which may be pregnant or lactating. There are a few water troughs holding 100 gallons of water. Lactating mares have substantially higher water requirements due to the fluid demands of milk production—typically 50–70 litres (13–18 gallons) per day, compared with 25–45 litres (6–12 gallons) for non-lactating horses. The fact that the foal was observed at the river infrequently suggests the dam may have had limited access to water and could have been dehydrated. Insufficient water intake can reduce milk production, compromising the foal’s hydration and nutrition. In herd settings, restricted or hierarchical access to water sources—especially where dominant stallions drink first—may further disadvantage mares with foals, increasing the risk of dehydration and related stress in both dam and offspring.

Additionally, one member of the Management Group was ordered to direct horses away from Rainna, the new foal. This is incredibly dangerous because the dam is potentially in post-partum oestrus. Do not approach wild horses this closely under ANY circumstances, particularly horses that have lost their fear of humans.

Behind Salt River Management Compound along the Beeline Highway, horses have access to several (5+/-) 100-gallon water troughs. The table shows the water requirements for horses, and while they can go to the river a few miles away, most remain.

Herd size	Stallions	Non-lactating mares	Lactating mares	Foals	Gallons/day (baseline)	100 gal troughs containers needed (baseline)	Extra refills needed	Gallons/day (hot)	100 gal	Extra refills needed beyond 5 (hot)
25	11	12	1	1	253	3	0	375	4	0
30	14	12	2	2	306	4	0	450	5	0
35	16	15	2	2	356	4	0	525	6	1
40	18	18	2	2	406	5	0	600	6	1
45	20	21	2	2	456	5	0	675	7	2
50	22	24	2	2	506	6	1	750	8	3
55	25	24	3	3	559	6	1	825	9	4
60	27	27	3	3	609	7	2	900	9	4
65	29	30	3	3	659	7	2	975	10	5
70	32	30	4	4	712	8	3	1050	11	6
75	34	33	4	4	762	8	3	1125	12	7
80	36	36	4	4	812	9	4	1200	12	7
85	38	39	4	4	862	9	4	1275	13	8
90	40	42	4	4	912	10	5	1350	14	9
95	43	42	5	5	965	10	5	1425	15	10
100	45	45	5	5	1015	11	6	1500	15	10

Perinatal, Disease, and Environmental Mortality

The death of foals occurs through multiple causes, which include dystocia, trauma, failure of passive transfer, septicemia, and environmental exposure (Greger PD and Romney EM, 1999; Roelle JE et al., 2010). The combination of long-distance mare migrations to water sources leads to increased risk of foal abandonment and death from starvation and heat exhaustion. The Nevada herds experienced foal deaths when stallions attacked their young during harem conflicts, demonstrating how population density can drive social aggression that affects reproductive timing.

Bachelor Stallion Aggression and Infanticide

The excess of male horses in the population creates an unbalanced sex ratio, leading to increased aggression among stallions (Berger, 1986; Ransom, J.I., and Cade, 2009). The prolonged battles between bachelor stallions lead to band takeovers and mares experience harassment, which results in foal injuries or deaths through trampling and targeted attacks during harem disruptions (Roelle JE et al., 2010; Greger PD and Romney EM, 1999). The behaviour of killing unrelated foals by new males is an adaptive yet destructive practice observed in other equid species.

Stallions become more aggressive because they have limited access to mares, and their poor nutritional state creates social instability in overpopulated systems. The prolonged stress from harassment causes mares to develop elevated cortisol levels, which leads to reproductive suppression and breaks down social bonds between band members, thus worsening demographic outcomes (Ransom JI et al., 2014).

The video below demonstrates bachelor aggression towards a young foal. It may upset some viewers; however, the foal was fine.
The entire post is here

Fertility Control: PZP Versus GonaCon and Behavioural Implications

The implementation of fertility control measures for non-lethal herd management affects social structures and death rates.

The PZP fertility control method used in free-roaming horse populations stops fertilisation but creates delays in conception and disrupts foaling synchronisation. The extended predation period results from delayed foaling times because PZP contraception leads to more miniature foals who become vulnerable to cougar attacks (Boyce PN and McLoughlin PD, 2021). The GnRH immunocontraceptive GonaCon functions as a reproductive hormone suppressor, affecting both male and female animals to prevent estrus and delay or stop reproductive cycles. The effectiveness of GonaCon in reducing foaling rates leads to different social changes than PZP does. The suppression of reproductive hormones by GonaCon creates stable band behaviour because it eliminates sexual cues, which reduces stallion competition and decreases the chances of aggression and infanticide. The extended period of reproductive behaviour suppression induced by GonaCon treatment might cause stallions to leave their non-receptive mares, as they lose their natural bonding signals.

Research findings on these vaccines remain scarce, but observations indicate that GonaCon-treated horse populations exhibit less aggressive behaviour than PZP-treated populations during the breeding season (Ransom JI et al., 2014). The high population density creates extreme competition between animals, which leads to foal injuries and deaths even when using different contraception methods. The combination of hormonal suppression with GonaCon treatment helps control foal deaths from infanticide and injuries, but does not stop them from occurring when animals face extreme population pressure.

Integrated Interpretation

The combination of seasonal predator attacks, density-related food scarcity, and reproductive social patterns leads to the death of foals in free-ranging horse populations. The Salt River’s overpopulation creates conditions where female cougars can predictably hunt foals. At the same time, male aggression and competition for resources lead to additional foal deaths through social conflicts and physical harm. The selection of fertility control methods affects social dynamics because PZP prolongs foal exposure to danger through delayed births, but GonaCon decreases aggressive and infanticidal conduct by blocking oestrous cycles. Successful population management requires three essential components: reducing population density, selecting fertility control methods based on behavioural effects, and conducting ongoing assessments of both population statistics and animal well-being.

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Summary of Relative Mortality Causes (Most to Least Significant)

1. Predation by cougars, concentrated in late spring–early summer, accounts for the majority of documented foal deaths (<3 months).
2. Nutritional limitation and dehydration from overpopulation, drought, and poor forage quality, leading to starvation and higher predation vulnerability.
3. Social aggression and infanticide, amplified by overpopulation and foal heat estrus, with added risk under PZP contraception.
4. Perinatal complications, including dystocia, birth trauma, and maternal exhaustion.
5. Environmental exposure, accidental injury, and infectious disease are often secondary to other stressors.

Management Implications:

• Reduce herd density toward ecological carrying capacity (100–200 animals for Salt River).
• Prioritise GonaCon over PZP in high-density, aggression-prone herds to suppress foal heat and reduce infanticide.
• Coordinate fertility control with habitat restoration, water management, and behavioural monitoring.
• Recognise that effective management must balance population control, social stability, and foal welfare across ecological and behavioural dimensions.

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In summary:
Foal mortality in overpopulated free-roaming herds arises primarily from predation, followed by nutritional stress, social aggression and foal heat–related infanticide, perinatal complications, and environmental or infectious factors. Overpopulation magnifies all mortality pathways. Management strategies emphasising density reduction, behaviorally informed fertility control (GonaCon), and habitat restoration offer the best prospects for improving foal survival and ecological balance.

The Salt River herd experiences higher foal death rates because of its dense population, which creates multiple factors that lead to increased mortality. The competition for resources between horses and their environment leads to poor mare body condition, which weakens foal health and raises their risk of dying early. Research on free-roaming horses shows that population density and restricted habitats lead to lower foal survival rates.

The Salt River Wild Horse Management Group reports that Salt River foal survival rates reach only 70% during their first year of life. Salt River Wild Horse Management Group. The Salt River Wild Horse Management Group observes that foal deaths occur because of social conflicts between bachelor stallions, which become more severe when band numbers increase in densely populated areas. (https://saltriverwildhorsemanagementgroup.org/on-this-foal-friday-we-have-good-news-and-bad-news/?)

The combination of high animal numbers at water sources creates conditions that increase foal dehydration and trauma risks, according to research on feral horses and ungulates, which shows density affects juvenile survival through maternal health, resource competition, and environmental stress.
The current evidence indicates that Salt River herd overpopulation leads to higher foal mortality rates, making density management essential to protect foal survival and maintain herd health.

References

1. Turner JW Jr, Wolfe ML, Kirkpatrick JF. Seasonal mountain lion predation on a feral horse population. Can J Zool. 1992;70:929-934.
2. Andreasen AM, Stewart KM, Longland WS, Beckmann JP. Prey specialization by cougars on feral horses in a desert environment. J Wildl Manag. 2021;85:1104-1120.
3. Knopff KH, Knopff AA, Kortello A, Boyce MS. Cougar kill rate and prey composition in a multiprey system. J Wildl Manag. 2010;74:1435-1447.
4. Bostal F, Scorolli AL, Zalba SM. The comeback of a top predator and its effects on a population of feral horses. Perspect Ecol Conserv. 2025;23:121-129.
5. Arizona Department of Agriculture. Salt River Horse Management Plan. Phoenix, AZ: AZDA; 2025.
6. Greger PD, Romney EM. High foal mortality limits growth of a desert feral horse population in Nevada. Great Basin Nat. 1999;59:374-379.
7. Roelle JE, Singer FJ, Zeigenfuss LC, Ransom JI, Coates-Markle L, Schoenecker KA. Demography of the Pryor Mountain Wild Horses, 1993–2007. US Geol Surv Sci Invest Rep. 2010-5125.
8. Berger J. Wild Horses of the Great Basin: Social Competition and Population Size. Chicago, IL: University of Chicago Press; 1986.
9. Ransom JI, Cade BS. Quantifying equid social behavior: a review of current research and future directions. Appl Anim Behav Sci. 2009;120:1-11.
10. Ransom JI, Kaczensky P, Lubow BC, et al. Influence of demography and social stress on feral horse reproduction. J Wildl Manag. 2014;78:916-925.
11. Kirkpatrick JF, Turner JW Jr. Achieving population goals in wild horses with fertility control: science and social context. Wildl Soc Bull. 2011;35:102-110.

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Comparative Analysis of Quadrupedal Gallop and Gait Studies: The rotary gallop

Galloping in quadrupeds has been extensively studied to understand the mechanics, energetics, and evolutionary adaptations of various species. The selected studies examine the differences between transverse and rotary gallops, the role of body morphology, such as centre of mass offset, in mechanical models of locomotion, and the application of gait analysis in horses and other cursorial mammals. The rotary gallop is more commonly observed in animals with flexible backbones, such as cats (including cheetahs) and certain dogs such as greyhounds and whippets. We examined thousands of our photos and found two mustangs using a rotary gallop.

Bertram and Gutmann examined the fundamental mechanics of gallop and identified a crucial difference between transverse and rotary forms. Horses epitomize the transverse gallop, where the hindlimbs initiate the center of mass directional transition, a dynamic compared to a skipping stone. Cheetahs use a rotary gallop, with the forelimbs starting the motion like in human running.  This distinction highlights how each gallop type optimizes momentum transfer and energy efficiency in relation to species-specific
morphology and performance requirements¹.

Yamada et al. further investigated gallop selection through a modeling study focused on horses. Their work demonstrated that the anterior offset of the horse’s center of mass enhances stability and makes the transverse gallop more effective at high speeds. Simulations confirmed that transverse gallop is mechanically optimal given the horse’s morphology. This supports the idea that body structure, particularly center of mass placement, constrains and dictates gait choice across species².

Parra et al. compared two leg dynamic models—MMS (Mass-Moment-Spring) and SLIP (Spring Loaded Inverted Pendulum)—in the context of galloping quadrupeds. Their results showed that rotary gallop species, such as cheetahs and greyhounds, exhibited higher bending moments and greater capacity for elastic energy storage, enabling rapid acceleration. Conversely, transverse gallop species, including horses and alpacas, produced greater maximum bending moment at forelimb initiation, emphasizing stability and endurance. Importantly, the MMS model, which accounts for leg mass, provided more accurate representations of trunk mechanics than the SLIP model³.

Barrey reviewed the methods, applications, and limitations of equine gait analysis, focusing on the use of kinetic, kinematic, and accelerometric approaches. Gait analysis was shown to be essential in quantifying lameness and evaluating training effects, with stride length and frequency strongly correlated to physiological responses. While laboratory-based tools such as force plates and accelerometry provided detailed insights into gait asymmetry, the translation of these advanced techniques into practical field applications remained limited. Nonetheless, the study emphasized that equine biomechanics has matured into a discipline with important clinical and performance applications⁴.

Together, these studies highlight that gallop type is closely linked to limb initiation strategy and body morphology. Horses, with an anterior centre of mass, favour the transverse gallop for stability and endurance, while cheetahs employ the rotary gallop for speed and agility. Comparative modeling demonstrates how mechanical structures drive these differences, and gait analysis provides practical tools for applying biomechanical insights in veterinary medicine and performance training.

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Below a stallion gallops across Sand Wash Basin in 2015 utilizing a rotary gallop. In photo 4, you can see the rotary stride.

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The bay stallion below from Little Book Cliffs, demonstrates the extended stride of a rotary gallop.

In the image below, the stallion could either be jumping over an obstical, or about to extend both forelegs in a rotary stride.

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Prevalence in horses

Breed

• Most horses use the transverse gallop almost exclusively.
• Rotary gallop is typical of extreme speed specialists like greyhounds and cheetahs. In horses, it shows up rarely, usually at maximal effort.
• Some anecdotal reports suggest Thoroughbreds (racehorses) are more likely to show a rotary sequence when pushed to top racing speed, but formal kinematic studies show the transverse gallop dominates across equine breeds (including Thoroughbreds, Arabians, Standardbreds, and Quarter Horses).

Age

• Foals sometimes experiment with rotary sequences in play, since they try out a variety of limb coordination patterns before settling into the adult repertoire.
• Adults overwhelmingly use transverse gallop, unless pushed into unusual conditions (fatigue, uneven terrain, or sprinting).

Gender (Sex)

• No evidence that mares, geldings, or stallions differ in gait type. The mechanics are biomechanical, not gender-related.

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References

1. Bertram JEA, Gutmann A. Motions of the running horse and cheetah revisited: fundamental mechanics of the transverse and rotary gallop. J R Soc Interface. 2008;6(35):549-559. doi:10.1098/rsif.2008.0328.
2. Yamada T, Aoi S, Adachi M, Kamimura T, Higurashi Y, Wada N, Tsuchiya K, Matsuno F. Center of mass offset enhances the selection of transverse gallop in high-speed running by horses: a modeling study. Front Bioeng Biotechnol. 2022;10:825157. doi:10.3389/fbioe.2022.825157.
3. Parra EA, García-Díaz V, Díaz-Rodríguez M, Quintero JE. Comparison of leg dynamic models for quadrupedal running: MMS vs. SLIP. Sci Rep. 2022;12:14579. doi:10.1038/s41598-022-18536-7.
4. Barrey E. Methods, applications and limitations of gait analysis in horses. Vet J. 1999;157(1):7-22. doi:10.1053/tvjl.1998.0301.

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Pre-domestication (Wild Horses, 35,000–10,000 years ago)

The Early Domestication period at Botai

The Early Domestication period at Botai spanned from 3500 BCE to 3000 BCE. The three primary coat colours of bay, black, and chestnut spread widely while dun remained present but became less common (Outram et al., 2009).

The Bronze Age spanned from 3000 BCE until 1000 BCE.

The domestic horse population started to develop new genetic traits, which included the cream dilution (CR) responsible for palomino and buckskin colours and the silver dilution (Z) that lightens black pigmentation and creates flaxen manes and tails (Reissmann & Ludwig, 2013). The presence of pinto spotting (tobiano/overo) in horses from Hungary and Siberia became evident through ancient DNA analysis during the time period between 2500 BCE and 2000 BCE (Ludwig et al., 2009). The research of Wutke et al. (2016) discovered tobiano spotting in horses from Botai, Kazakhstan, and Germany, which dates back to 3600–3300 BCE and 3300 BCE, respectively, showing that tobiano existed during the first domestication period. The first appearance of polygenic white markings, which include stars, blazes, socks, and stockings, occurred in Bronze Age genomes as evidence of early selection for decorative traits (Pruvost et al., 2011).

The Iron Age and Antiquity (1000 BCE to 500 CE)

The STX17 duplication, known as the grey mutation, emerged between 200 BCE and 200 CE, and then spread quickly because people valued its visual appeal and symbolic meaning (Royo et al., 2008). The grey horse colouration emerges at birth but develops depigmentation as the animal ages, which distinguishes it from previous stable genetic mutations. The frequency of sabino and tobiano spotting patterns rose significantly during the Late Bronze and Iron Ages until tobiano reached its peak at 19% in Iron Age horses (Wutke et al., 2016). The depiction of pinto and leopard-spotted horses in Scythian, Celtic, and Roman art from ancient times demonstrates that patterned horse coats became widespread throughout Eurasia (Ludwig et al., 2009).

The Early Modern Period (500 CE to 1500 CE).

The research by Wutke et al. (2016) demonstrates that the occurrence of spotted and diluted coat patterns decreased dramatically throughout the Middle Ages, while solid coat colours, particularly chestnut, became more prevalent. The Roman Empire’s collapse and subsequent decline in breeding practices reduced the need for horse identification. Additionally, possible religious and cultural meanings associated with apocalyptic riders and church art may have contributed to this colour shift. The pearl dilution allele first appeared in medieval Iberian, German, and Slovakian horses, according to Wutke et al. (2016), but its presence remained limited to Iberian regions. The Iberian and baroque breeds maintained their preference for grey horses while Spanish-introduced leopard-spotted horses evolved into the contemporary Appaloosa breed (Wutke et al., 2016). The period between 1500 CE and the present day marks the beginning of the Post-Medieval to Modern era.

The roan pattern emerged as a result of the KIT allele, but scientists discovered it through European draft breeds before it spread to American stock horses (Holl et al. 2019). The KIT gene mutation SB1 leads to irregular white markings on legs and face with roaned edges, which scientists discovered in Clydesdales and Tennessee Walkers during the domestication period (Haase et al. 2007). The genetic basis of Rabicano remains unknown; however, scientists agree it developed during the domestication period because it affects Arabians and Thoroughbreds (Imsland et al. 2015). The genetic basis of flaxen remains unknown because it lightens chestnut manes and tails through multiple genetic factors. At the same time, sooty creates dark hair patterns on the topline, which scientists first documented during modern times (Holl et al. 2019). The mushroom dilution mutation in Shetland ponies results from a recessive MFSD12 mutation, which produces a sepia-colored chestnut coat with lightened mane and tail, and scientists believe it emerged recently (Ishida et al. 2015). The champagne dilution mutation in SLC36A1 occurred within the past few hundred years and now affects many American stock and gaited breeds (Cook et al. 2008). The pearl gene functions as a recessive dilution factor, which comes from Iberian origins and produces pale coat colours when horses have two copies of the gene or when they carry the cream gene (Wutke et al. 2016). The Dominant White alleles represent the newest group of mutations, which include more than 30 independent KIT mutations that result in white or nearly white foals at birth, and these mutations emerged during the last few centuries from specific founder horses in Thoroughbreds, Arabians, and Quarter Horses (Haase et al. 2009).

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Chronological Order of Horse Coat Colors

Pre-domestication (Pleistocene / Ice Age Horses, >30,000 years ago)
Bay (wild-type) — ancestral color.
Dun (primitive dilution with dorsal stripe, leg barring).
Black (MC1R mutation).
Chestnut (MC1R e/e mutation).
Leopard complex (Appaloosa spotting, LP) — confirmed ~25,000 years ago (Pech-Merle cave horses).
Pangaré (mealy shading, light muzzle/belly, primitive modifier).
Sooty (countershading/black hairs through coat).

Early Domestication (Botai ~3500–3000 BCE)
Polygenic white markings (stars, blazes, socks, stockings).
Tobiano spotting — detected in Eneolithic/Copper Age horses (~3600–3300 BCE; Botai and Germany)

Bronze Age (3000–1000 BCE)
Cream dilution (CR) — palomino, buckskin.
Silver dilution (Z) — dilutes black, light mane/tail.
Sabino-1 (SB1, KIT) — introduced after domestication; confirmed in Bronze Age samples.

Iron Age / Antiquity (1000 BCE–500 CE)
Grey (STX17 duplication) — appears ~200 BCE–200 CE.

Medieval (500–1500 CE)
Pearl dilution (prl, MATP gene) — first detected in medieval Iberian and European horses

Post-Medieval to Modern (1500 CE–present)
Roan (KIT allele) — absent in ancient DNA, appears in European draft breeds, later in stock breeds.
Rabicano — flank/tailhead roaning, genetic basis unknown, only in domestic horses.
Flaxen — light mane/tail on chestnut; polygenic modifier.
Mushroom (MFSD12 mutation) — sepia chestnut, Shetland ponies.
Champagne (SLC36A1 mutation) — American stock and gaited breeds.
Dominant White (multiple KIT mutations, W1–W30+ ) — independent, breed-specific, recent mutations.

Summary
Oldest: Bay, dun, black, chestnut, leopard complex (Ice Age horses).
Early domestication (~3500 BCE): white markings, tobiano.
Bronze Age: cream, silver, sabino.
Iron Age (~200 BCE): grey.
Medieval (~500–1500 CE): pearl.
Modern (1500 CE–present): roan, rabicano, flaxen, mushroom, champagne, dominant white.(Palomino, Buckskin, Smokey Black),

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Dr. Meredith Hudes-Lowder
September 13, 2025

References

• Cook, D., Brooks, S., Bellone, R., & Bailey, E. (2008). Missense mutation in exon 2 of SLC36A1 responsible for champagne dilution in horses. Genomics, 92(2), 93–98.
• Haase, B., Brooks, S. A., Schlumbaum, A., Azor, P. J., Bailey, E., Alaeddine, F., … Poncet, P. A. (2007). Allelic heterogeneity at the equine KIT locus in dominant white (W) horses. PLoS Genetics, 3(11), e195.
• Haase, B., Rieder, S., Tozaki, T., & Brooks, S. A. (2009). Five novel KIT mutations in horses with white coat colour phenotypes. Animal Genetics, 40(5), 623–629. https://
• Holl, H. M., Brooks, S. A., Bailey, E., & Mack, M. (2019). Equine coat color genetics. In T. R. Famula, E. Cothran, & M. Bowling (Eds.), Equine Genetics (2nd ed., pp. 83–104). Wiley.
• Imsland, F., Reissmann, M., & Andersson, L. (2015). Epistatic and pleiotropic effects of coat colour genes in horses. Animal Genetics, 46(5), 407–417.
• Ishida, N., Hasegawa, T., Takeda, K., Sakagami, M., Onuki, A., Inoue-Murayama, M., … Mukoyama, H. (2015). A frameshift mutation in the MFSD12 gene is associated with the mushroom coat color dilution in Shetland ponies. BMC Genetics, 16, 101.
• Ludwig, A., Pruvost, M., Reissmann, M., Benecke, N., Brockmann, G. A., Castaños, P., … Hofreiter, M. (2009). Coat color variation at the beginning of horse domestication. Science, 324(5926), 485.
• Outram, A. K., Stear, N. A., Bendrey, R., Olsen, S., Kasparov, A., Zaibert, V., Thorpe, N., & Evershed, R. P. (2009). The earliest horse harnessing and milking. Science, 323(5919), 1332–1335.
• Pruvost, M., Bellone, R., Benecke, N., Sandoval-Castellanos, E., Cieslak, M., Kuznetsova, T., … Ludwig, A. (2011). Genotypes of predomestic horses match phenotypes painted in Paleolithic cave art. Proceedings of the National Academy of Sciences, 108(46), 18626–18630.
• Royo, L. J., Álvarez, I., Beja-Pereira, A., Molina, A., Fernández, I., Jordana, J., Gómez, E., Goyache, F., & Cañón, J. (2008). The origins of the grey phenotype in horses. Nature Genetics, 40(8), 1004–1007.
• Reissmann, M., & Ludwig, A. (2013). Pleiotropic effects of coat colour-associated mutations in humans, mice and other mammals. Seminars in Cell & Developmental Biology, 24(6–7), 576–586.
• Wutke, S., Benecke, N., Sandoval-Castellanos, E. et al. Spotted phenotypes in horses lost attractiveness in the Middle Ages. Sci Rep 6, 38548 (2016). https://doi.org/10.1038/srep38548

Dr Meredith Hudes-Lowder: Biostatistician

Historical perspective

Free-roaming horse herds in the West are combinations of domestic lineages, not unique taxa. Peer-reviewed studies and federal reports indicate that U.S. free-roaming herds are formed from various breeds and sources, including ranch stock and tribal herds. For instance, a genetic analysis of Theodore Roosevelt National Park, a well-documented example, reveals that Western rangelands have historically received horses from diverse origins and breeds (Thomas, 2024). Horses in the park likely originated from multiple sources, a typical pattern for U.S. feral herds.

The National Academies’ review of BLM genetics lists a few herds with evidence of old Spanish bloodlines, such as those in the Cerbat Mountains of Arizona, the Pryor Mountains of Montana, and Sulphur in Utah. Salt River is not on this list, highlighting that it is not a distinct genetic population that needs specific preservation. National Park Service sites consistently describe free-roaming horses as non-native, feral descendants of domestic stock, not as a separate wildlife species.

“Extinction” is not the right term; the real risk is local extirpation. By definition, extinction refers to the worldwide loss of a species, whereas extirpation denotes the disappearance of a species from a particular area, even as it continues to exist elsewhere. If a local herd disappears, that means it has been extirpated, not extinct. Looking at horses: the domestic species Equus caballus is plentiful, with about 6.65 million domestic horses in the U.S. (2023 American Horse Council) and around 73,000 free-roaming horses and burros on BLM lands (2025). A local decline at Salt River cannot result in species-level “extinction.”

If genetic health is the concern, it can be addressed without exaggerating census numbers. Standard conservation practice for feral herds involves monitoring diversity and, if necessary, introducing outside genetic stock. This is precisely what peer-reviewed studies suggest when diversity is low, such as in TRNP. In other words, genetic viability is managed through breeding contributions and gene flow, not by claiming a unique lineage at Salt River.

In summary, the Salt River herd is a historical grouping of formerly domestic horses, not a unique taxon. Federal reports recognize only a few Spanish-lineage herds elsewhere. Using accurate terminology, the worst-case biological outcome is local extirpation, not extinction. Even local genetic risks are manageable with standard tools, such as monitoring and, if needed, introductions.

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Introduction: The genetic problem we’re solving

The Salt River Herd’s long-term health depends on maintaining enough genetic diversity to adapt to drought, disease, and habitat change. The single best indicator of how fast diversity erodes is adequate population size (Ne)—the number of animals that actually pass genes to foals—rather than the raw headcount (N) (Waples et al., 2013; Nunney, 1993). In free-ranging, polygynous horses, Ne is usually lower than N because a few stallions sire a disproportionate share of foals, and age/sex structure is uneven (Waples et al., 2013; Nunney, 1993). Modern conservation guidance therefore manages to set Ne targets explicitly—keep Ne ≳ 50 to limit short-term inbreeding and push higher when possible for long-term adaptability—rather than working to census alone (Frankham et al., 2014a, 2014b). We will treat genetic diversity as a routine management outcome and show it on the same dashboard as foaling rate and habitat metrics (Hoban et al., 2021; Andersson et al., 2022).

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What determines genetic viability (and why headcount isn’t enough)

Who breeds matters more than who is present. A manager-friendly relation explains why male monopolies depress Ne:

Here, Nm and Nf are the numbers of breeding stallions and mares, respectively (Waples et al., 2013; Nunney, 1993). If only a few stallions dominate paternity, Ne stays low no matter how many mares are on the landscape. Genetic drift then chips away at diversity every generation, which is why holding Ne near or above ~50 measurably slows loss across horse-length timeframes (Frankham et al., 2014a). Conversely, spreading reproduction across more stallions and enough mares lifts Ne at the same census size. For example, moving from roughly 12 breeding stallions/35 breeding mares (Ne ≈ 36) to ~20 breeding stallions/40 breeding mares (Ne ≈ 53) crosses the short-term safety threshold without increasing total herd size—purely by broadening who contributes (Waples et al., 2013).

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What can we do to maintain the genetic health of the Salt River?

Measure smart, noninvasively. We will establish a genetic baseline using fecal DNA (fresh, air-dried in paper bags), then re-sample every two years. Labs will pre-screen extracts by qPCR, use replicate genotyping, and track error rates to ensure reliability (King et al., 2018; Hausknecht et al., 2010). Routine outputs: Ne (linkage-disequilibrium estimators), heterozygosity, allelic richness, and—when blood/tissue SNPs are available—runs of homozygosity (ROH) to detect recent inbreeding (Colpitts et al., 2022; Andersson et al., 2022).

Manage breeding probabilities (without assigning mates).

Broaden stallion contribution: use contraception and removal priorities to prevent a few males from monopolizing paternity; the goal is ~18–22 effective breeding stallions alongside ~35–40 breeding mares, which typically yields Ne ≈ 50–55 at N ≈ 100 (Waples et al., 2013; Nunney, 1993).

Rotate contraception by lineage: keep contraception on standard lines; off for 1–2 seasons for under-represented lines so their foals enter the crop (Nuñez et al., 2017).

Pick the right tool, measure the tradeoffs: PZP often extends receptive behavior and increases mare band-switching (lower mare fidelity), reshuffling who breeds (Nuñez et al., 2009; Nuñez et al., 2010; Madosky et al., 2010; Jones & Nuñez, 2019). GnRH immunocontraception (e.g., GonaCon-type) can suppress fertility with no deleterious breeding-season behavioral effects when implemented carefully (Ransom et al., 2014). We will track mare band-change rates and the number of effective breeding stallions alongside genetic metrics to adjust dosing in real-time (King et al., 2021; Nuñez et al., 2017; Jones et al., 2020).

Avoid genetically biased removals: when removals/adoptions are required, retain animals carrying rare alleles or representing under-sampled lines. Use pedigree-aware tools such as PMx where pedigrees exist, or molecular kinship rules where they do not (Lacy et al., 2011; Putnam & Ivy, 2014).

Use “natural” gene flow when available: occasional 5–10% cross-boundary inflow from neighboring jurisdictions (e.g., Fort McDowell Yavapai Nation; Salt River Pima–Maricopa Indian Community) is not guaranteed but has occurred; when newcomers appear, document immediately, pause contraception on immigrant mares, and avoid removing immigrant stallions until they’ve contributed foals—this raises NmN_mNm​ and lowers variance in family size, boosting Ne (King et al., 2018; Waples et al., 2013; Nunney, 1993).

If trends still slip: implement small, screened genetic rescue (a few unrelated immigrants over several years) using standard outbreeding-risk safeguards (Frankham et al., 2011; Frankham et al., 2014a, 2014b).

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Refuting the “low numbers = extinction” claim “

Too few horses means inevitable extinction” is incorrect because extinction risk is not determined by census size alone. What matters genetically is Ne, which we can measure and manage. A herd of ~100 can maintain a population of 50 or more when reproduction is spread across around 20 stallions and 35–40 mares (Waples et al., 2013; Nunney, 1993). Ongoing noninvasive monitoring lets us detect drift or inbreeding early and adjust contraception/removals accordingly (King et al., 2018; Andersson et al., 2022). If needed, even small gene flow—natural cross-boundary movement or a carefully screened introduction—has repeatedly improved diversity and fitness in small populations (Frankham et al., 2011; Frankham et al., 2014a, 2014b). The cautionary case is closed, isolated systems like Sable Island, which persist at modest size but accumulate ROH and inbreeding over time—underscoring that management plus occasional gene flow, not inflated census, is the remedy (Plante et al., 2007; Colpitts et al., 2022; Colpitts, 2024). In short: a well-managed, moderately sized Salt River Herd can remain genetically viable without overshooting ecological limits, provided we monitor Ne and act on the results. Why genetics matter. 

Genetic diversity is crucial for a free-roaming herd’s ability to adapt to internal and external forces. It helps maintain options when weather, disease, or habitat conditions change. The most useful measure for tracking how quickly this capacity declines is effective population size (Ne). This number represents the animals that actually pass genes to foals. In free-ranging horses, Ne is often lower than the total number of horses. This occurs because a few stallions sire many foals and there is an uneven distribution of age and sex classes (Waples et al., 2013; Nunney, 1993). Modern recommendations set clear Ne targets. Keep Ne at or above 50 to reduce short-term inbreeding and increase it when possible for long-term adaptation. Genetic diversity should be a routine management goal, not an afterthought (Frankham et al., 2014a, 2014b; Hoban et al., 2021; Andersson et al., 2022).

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What drives Ne, the number of reproducing horses?

Ne relies on who breeds, not just who is present. There is a practical connection between Ne and the number of breeding males and females. This highlights the negative impact of male monopolies: 

So, if only a few stallions (Nm) dominate offspring production, Ne remains low regardless of how many mares (Nf) foal (Waples et al., 2013; Nunney, 1993). Genetic drift reduces variation with each generation. Keeping Ne at or above about 50 significantly slows this decline across generations (Frankham et al., 2014a). The expected decrease in heterozygosity due to drift is given by:

 

Short-term bottlenecks have a significant impact because the harmonic mean influences long-term Ne: 

Variance in family size, such as a few stallions producing many foals, further lowers Ne like this: 

(Nunney, 1993; Waples et al., 2013).   

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How to measure all of this without roundups. 

Fresh fecal pellets contain enough sloughed cells for individual identification and population-genetic studies. Air-drying these pellets in paper bags often yields better results than using ethanol for PCR, especially in arid areas (King et al., 2018). Accuracy improves if labs pre-screen DNA extracts using qPCR to filter out low-quality samples and implement replicate genotyping with negatives to minimize errors (Hausknecht et al., 2010). Aside from classic measures such as heterozygosity and allelic richness, it can also include user-friendly indicators on dashboards to keep non-genetic audiences informed about progress (Andersson et al., 2022; Hoban et al., 2021). We plan to include this in our Salt River Horse Registry Database^tm or other similar monitoring programs at other management areas. When blood or tissue samples are available, genome-wide SNPs allow for the calculation of runs of homozygosity (ROH) and a genomic inbreeding fraction: 

This is sensitive to recent inbreeding and small Ne (Colpitts et al., 2022). Cases from Sable Island illustrate this pattern. Early microsatellite studies described diversity within a closed herd. Later ROH mapping showed significant genomic markers of drift and inbreeding. A recent dissertation links those genomic trends to demographics and ecology, with clear implications for management (Plante et al., 2007; Colpitts et al., 2022; Colpitts, 2024). Small and isolated herds on Greek islands demonstrate how geography and history can rapidly lead herds to different genetic baselines. This means that goals and strategies should consider the local context (Katsoulakou et al., 2023).  

Total round costs of Genetic Analysis

Two ready-to-use budgeting scenarios

A grant could be obtained for the studies

A) Baseline genetics (Salt River–style), n = 80 fecal samples

• Extraction (80× $16) ≈ $1,280. fees.oregonstate.edu
• qPCR prescreen (plate-based; modest line item). PMC
• Microsat PCR + fragment analysis + scoring (assume $60–$120 per successful sample) → $4,800–$9,600. The University of Alabama at Birmingham and Texas A&M University-Corpus Christi
• Baseline lab subtotal ≈ $6.1k–$11.0k (add reporting/PI time as needed).
  (If you outsource end-to-end to a wildlife genetics provider, expect a single per-sample quote that folds these in.)

B) Monitoring cycle, n = 50 fecal samples

• Extraction ≈ $800. fees.oregonstate.edu
• Microsat + scoring (assume $60–$120 each) → $3,000–$6,000. The University of Alabama at BirminghamTexas and A&M University-Corpus Christi
• Monitoring lab subtotal ≈ $3.8k–$6.8k.

If you add hair/blood SNP arrays on a handled subset, reagent list prices start at $35 per array (processing extra) and require high-quality DNA; plan $100–$200+ per sample all-in for service providers. Use arrays to map relatedness/ROH, but rely on microsats for routine fecal rounds. Neogen and Thermo Fisher Scientific

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Contraception, social structure, and genetics. 

Contraception can support genetic goals, but different methods can affect social structure, which impacts the equations above through Nm and Vk. PZP prevents fertilization and is associated with more extended periods of receptivity and increased band-switching (lower mare fidelity). This reshuffle mating opportunities and often increases male competition (Nuñez et al., 2009; Nuñez et al., 2010; Madosky et al., 2010; Jones & Nuñez, 2019; Jones et al., 2020). GnRH immunocontraception, like GonaCon-type programs, acts higher up the endocrine pathway. Field studies indicate reliable fertility suppression without adverse behavioral effects during the breeding season when applied carefully. However, any handling or culling can still change behavior and should be monitored (Ransom et al., 2014). Recent research also shows how habitat and social conditions influence actual breeding (King et al., 2025) and how social instability may increase female aggression, altering breeding opportunities (Nunez & Adelman, 2025). In practice, select a mix of contraception that aligns with dart access and desired group stability. Monitor mare band-change rates and the number of effective breeding stallions while tracking genetic metrics to allow for adjustments (Nuñez et al., 2017; King et al., 2021).  

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Potential cross-boundary inflow (Fort McDowell Yavapai Nation; Salt River Pima–Maricopa Indian Community). 

Occasional inflows of 5–10% new horses from nearby areas can happen, but they are not guaranteed. These inflows should be considered opportunistic, natural genetic rescue—a benefit to plan for but not rely on. Even a small number of newcomers can reduce drift and refresh rare alleles if those animals breed (Waples et al., 2013; Nunney, 1993; Frankham et al., 2014a). When and if newcomers are identified, follow these steps:

(1)   Document immediately with photo IDs and microchips if possible. Collect fecal DNA within 24–48 hours (King et al., 2018; Hausknecht et al., 2010);

(2)   Let them breed by pausing contraception on immigrant mares for one or two seasons and avoiding removal of immigrant stallions while proceeding with other removals. This increases Nm and lowers Vk, raising Ne;

(3)   Maintain contraception on well-represented resident lines to favor under-represented (including immigrant) lineages in producing foals (Frankham et al., 2014a; Nuñez et al., 2017);

(4)   Follow regular biosecurity and welfare checks

(5)   Re-estimate your metrics (Ne, heterozygosity, allelic richness, ROH; plus mare band-switching if PZP is utilized) in the next cycle (King et al., 2018; King et al., 2021).

Because space use influences gene flow, maintaining corridors and functional band ranges increases the chances that rare movements will occur and impact genetic diversity (King et al., 2021; King et al., 2025). Use standard outbreeding-risk safeguards to minimise risks—such as the same species, similar environments, and evidence of historical connectivity (Frankham et al., 2011).  

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Action plan (measure → interpret → act → re-measure). 

• Baseline this year. Gather fecal genotypes from most animals (for N ~100–150, aim for ~80 unique individuals). Link genetic IDs to photo IDs or microchips (King et al., 2018). 

• Every 2 years. Sample 40–60 unique individuals. Report Ne, heterozygosity, allelic richness, and, when available, ROH. If PZP is widely used, also report mare band-change rates (King et al., 2018; Nuñez et al., 2009; King et al., 2021). 

• Triggers. Green: Ne ≥ 50 and diversity stable—continue rotations. Yellow: Ne 35–49 or 5–10% diversity decline over 4 years—widen male participation (rotate contraception off under-represented mares; keep it on standard lines) and revisit removals to avoid losing rare lines. Red: Ne < 35 or fast-rising ROH—treat natural inflow as first-line genetic rescue. If this is insufficient, plan a small, screened introduction (Frankham et al., 2014a, 2014b; Andersson et al., 2022; Hoban et al., 2021; Colpitts et al., 2022; Colpitts, 2024). 

• During required removals/adoptions. Avoid choices biased by genetics: use molecular relatedness and allelic value to retain individuals from rare lines and reduce male monopolies. Use PMx to minimize mean kinship when pedigrees exist. When they do not, kinship-based molecular rules generally outperform random selection (Lacy et al., 2011; Putnam & Ivy, 2014). 

• Context matters. Larger, less dense ranges support more bands and lower male monopolies. In contrast, closed systems, such as Sable Island, and small islands, like those in Greece, accumulate inbreeding more quickly and require earlier, more cautious genetic intervention (Plante et al., 2007; Colpitts et al., 2022; Katsoulakou et al., 2023).    

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References

Andersson, A., Karlsson, S., Ryman, N., & Laikre, L. (2022). Monitoring genetic diversity with new indicators applied to an alpine freshwater top predator. Molecular Ecology, 31(24), 6422–6439. https://doi.org/10.1111/mec.16710

Colpitts, J. (2024). Causes and consequences of variation in genomic diversity in Sable Island feral horses (Doctoral dissertation). University of Saskatchewan.

Colpitts, J., McLoughlin, P. D., & Poissant, J. (2022). Runs of homozygosity in Sable Island feral horses reveal the genomic consequences of inbreeding and divergence from domestic breeds. BMC Genomics, 23(1), 501. https://doi.org/10.1186/s12864-022-08729-9

Frankham, R., Ballou, J. D., Eldridge, M. D. B., Lacy, R. C., Ralls, K., Dudash, M. R., & Fenster, C. B. (2011). Predicting the probability of outbreeding depression. Conservation Biology, 25(3), 465–475. https://doi.org/10.1111/j.1523-1739.2011.01662.x

Frankham, R., Bradshaw, C. J. A., & Brook, B. W. (2014a). Genetics in conservation management: Revised recommendations for the 50/500 rules, Red List criteria and population viability analyses. Biological Conservation, 170, 56–63. https://doi.org/10.1016/j.biocon.2013.12.036

Frankham, R., Bradshaw, C. J. A., & Brook, B. W. (2014b). 50/500 rules need upward revision to 100/1000 – Response to Franklin et al. Biological Conservation, 176, 254–255. https://doi.org/10.1016/j.biocon.2014.05.006

Hausknecht, R., Bayerl, H., Gula, R., & Kuehn, R. (2010). Application of quantitative real-time PCR for noninvasive genetic monitoring. Journal of Wildlife Management, 74(8), 1904–1910. https://doi.org/10.2193/2009-421

Hoban, S., Bruford, M. W., Funk, W. C., Galbusera, P., Griffith, M. P., Grueber, C. E., Heuertz, M., Hunter, M. E., Hvilsom, C., Stroil, B. K., Kershaw, F., Khoury, C. K., Laikre, L., Lopes-Fernandes, M., MacDonald, A. J., Mergeay, J., Meek, M., Mittan, C., Mukassabi, T. A., O’Brien, D., … Vernesi, C. (2021). Global commitments to conserving and monitoring genetic diversity are now necessary and feasible. BioScience, 71(9), 964–976. https://doi.org/10.1093/biosci/biab054

Jones, M. M., & Nuñez, C. M. V. (2019). Decreased female fidelity alters male behavior in a feral horse population managed with immunocontraception. Applied Animal Behaviour Science, 214, 34–41. https://doi.org/10.1016/j.applanim.2019.03.005

Jones, M. M., Proops, L., & Nuñez, C. M. V. (2020). Rising up to the challenge of their rivals: Mare infidelity intensifies stallion response to playback of aggressive conspecific vocalizations. Applied Animal Behaviour Science, 225, 104949. https://doi.org/10.1016/j.applanim.2020.104949

Katsoulakou, E. M., Papachristou, D., Kostaras, N., Laliotis, G., Bizelis, I., Cothran, E. G., Juras, R., & Koutsouli, P. (2023). Genetic variability of small horse populations from Greek islands. Black Sea Journal of Agriculture, 6(2), 117–125. https://doi.org/10.47115/bsagriculture.1165045

King, S. R. B., Schoenecker, K. A., Fike, J. A., & Oyler-McCance, S. J. (2018). Long-term persistence of horse fecal DNA in the environment makes equids particularly good candidates for noninvasive sampling. Ecology and Evolution, 8(8), 4053–4064. https://doi.org/10.1002/ece3.3956

King, S. R. B., Schoenecker, K. A., Fike, J. A., & Oyler-McCance, S. J. (2021). Feral horse space use and genetic characteristics from fecal DNA. Journal of Wildlife Management, 85(6), 1074–1083. https://doi.org/10.1002/jwmg.21974

King, S. R. B., Cole, M. J., & Schoenecker, K. A. (2025). Horse affairs: Factors affecting reproductive success in a feral polygynous ungulate. Animal Behaviour, 227, 123281. https://doi.org/10.1016/j.anbehav.2025.123281

Lacy, R. C., Ballou, J. D., & Pollak, J. P. (2011). PMx: Software package for demographic and genetic analysis and management of pedigreed populations. Methods in Ecology and Evolution, 3(2), 433–437. https://doi.org/10.1111/j.2041-210X.2011.00148.x

Madosky, J. M., Rubenstein, D. I., Howard, J. J., & Stuska, S. (2010). The effects of immunocontraception on harem fidelity in a feral horse (Equus caballus) population. Applied Animal Behaviour Science, 128(1–4), 50–56. https://doi.org/10.1016/j.applanim.2010.09.013

Nunez, C. M. V., & Adelman, J. S. (2025). Mean mares? Habitat features influence female aggression in response to social instability in the feral horse (Equus caballus). Biology Letters, 21(1), 20240494. https://doi.org/10.1098/rsbl.2024.0494

Nuñez, C. M. V., Adelman, J. S., Mason, C., & Rubenstein, D. I. (2009). Immunocontraception decreases group fidelity in a feral horse population during the non-breeding season. Applied Animal Behaviour Science, 117(1–2), 74–83. https://doi.org/10.1016/j.applanim.2008.12.001

Nuñez, C. M., Adelman, J. S., & Rubenstein, D. I. (2010). Immunocontraception in wild horses (Equus caballus) extends reproductive cycling beyond the normal breeding season. PLOS ONE, 5(10), e13635. https://doi.org/10.1371/journal.pone.0013635

Nuñez, C. M. V., Adelman, J. S., Carr, H. A., Alvarez, C. M., & Rubenstein, D. I. (2017). Lingering effects of contraception management on feral mare (Equus caballus) fertility and social behavior. Conservation Physiology, 5(1), cox018. https://doi.org/10.1093/conphys/cox018 Nunney, L. (1993). The influence of mating system and overlapping generations on effective population size. Evolution, 47(5), 1329–1341. https://doi.org/10.1111/j.1558-5646.1993.tb02158.x

Plante, Y., Vega-Pla, J. L., Lucas, Z., Colling, D., de March, B., & Buchanan, F. (2007). Genetic diversity in a feral horse population from Sable Island, Canada. Journal of Heredity, 98(6), 594–602. https://doi.org/10.1093/jhered/esm064

Putnam, A. S., & Ivy, J. A. (2014). Kinship-based management strategies for captive breeding programs when pedigrees are unknown or uncertain. Journal of Heredity, 105(3), 303–311. https://doi.org/10.1093/jhered/est068

Ransom, J. I., Powers, J. G., Garbe, H. M., Oehler, M. W., Nett, T. M., & Baker, D. L. (2014). Behavior of feral horses in response to culling and GnRH immunocontraception. Applied Animal Behaviour Science, 157, 81–92. https://doi.org/10.1016/j.applanim.2014.05.002

Thompson MA, McCann BE, Rhen T, Simmons R. Population genomics provide insight into ancestral relationships and diversity of the feral horses of Theodore Roosevelt National Park. Ecol Evol. 2024 Apr 1;14(4):e11197. doi: 10.1002/ece3.11197. PMID: 38571790; PMCID: PMC10985374.

Waples, R. S., Luikart, G., Faulkner, J. R., & Tallmon, D. A. (2013). Simple life-history traits explain key effective population size ratios across diverse taxa. Proceedings of the Royal Society B, 280(1768), 20131339. https://doi.org/10.1098/rspb.2013.1339

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This response confronts the inaccurate statements about the validity of the Salt River Vegetation Assessment. As a researcher, scientist, and biostatistician, I know the report is completely valid. However, not everyone has my background, so I provided scholarly proof that this type of ASSESSMENT (note the lack of the words “research study‘) is completely valid and scientifically grounded. The University of Arizona is a prestigious institution that would not produce anything inferior or lacking in the proper scientific rigour, methodological standards, or ecological relevance expected of land-grant university research and Extension work. Below is the Rebuttal, as well as an academic review of the assessment below the rebuttal.

Certain advocacy groups are criticizing the University of Arizona’s April 2025 Vegetation Assessment of the Salt River Horse Management Area, with The Salt River Wild Horse Management Group topping the list. These groups dispute its legitimacy because it was not published in a peer-reviewed journal. The argument shows a fundamental failure to understand how ecological monitoring and land management operate within practical settings. Please read the first few paragraphs. Also of note, this is written by a non-scientist, with no formal research training most likely named Simone Van der Salm (Netherlands is not her real name). Ms Van der Salm is the president of the Salt River Wild Horse Management Group and ironically, Ms Van der Salm is NOT a United States citizen, perhaps why she is at ease disparaging the University of Arizona.

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Professional range scientists and ecologists at the University of Arizona Cooperative Extension developed the technical field report, which serves as the vegetation assessment. The assessment provides documentation of actual conditions while guiding resource management choices and delivering scientifically sound data to stakeholders, including land agencies, tribal partners, and the general public.

The scientific validity of management-grade research does not depend on peer review processes. The assessment’s quality is independent of peer-reviewed publication status because this format is unnecessary for credibility. Technical reports, field surveys, and unpublished data serve as the foundation for timely decision-making in all land and wildlife agencies and the Bureau of Land Management and the Forest Service. These include:

• Grazing permit evaluations
• Drought response actions
• Wildlife habitat management
• Emergency ecological assessments

This “gray literature” constitutes the primary source of information for both National Environmental Policy Act (NEPA) decision-making and agency decisions according to the National Environmental Policy Act (NEPA).

The validity of work depends on different factors other than peer-review status.
The success of applied ecological work depends more on methodological rigor than on peer-review status. Standard sampling protocols (dry-weight rank, comparative yield), transparent site selection methods, and data collection procedures should be used.

• Methodological rigor
• Appropriate interpretation grounded in ecological science.
• Clear documentation of findings.

The April 2025 assessment meets all of these criteria. The evaluation applied recognized vegetation assessment protocols, which combined dry-weight rank and comparative yield to document the distinct characteristics between grazing and non-grazing areas.

What motivations stem from these attacks against the assessment?
This report faces invalidation because of its non-journal publication status, but this argument lacks scientific-basis and demonstrates political dishonesty. This attack aims to deceive the public and decision-makers by equating essential research publications with field-based environmental assessments, although these represent entirely different approaches with separate objectives.

The application of this standard would render all the following assessments invalid:

• Most agency-led rangeland evaluation
• Federal wildlife habitat reports
• Environmental impact assessments
• Tribal ecological inventories
• Emergency drought response protocols.

No serious scientist or land manager would accept that logic.

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