Wild Horses: Are They Being Managed to Extinction?


Because humans have eradicated most predators of wild horses, humans are the only means of wild horse population control. How many horses are too many? Probably a lot more than we have today.

Here are two interesting wild horse facts, reported with extensive scientific citations in Dan Flores’ American Serengeti: For hundreds of thousands of years before the Pleistocene extinctions, during that period of incredible biodiversity that ended 12,000 years ago when humans arrived in North America, horses represented 25 percent of the total Great Plains animal biomass. And during the early 1800s when wild horses briefly reestablished numbers as high as 2-million, horse biomass was around 10 percent of bison biomass — still only perhaps 1/5th their ancient number.

The rangelands need keystone grazing species like bison or cows, lots of prey and lots of predators. Remove any of these and rangelands and wildlife degrade. Put them all back and they recover. Within a healthy system wild horses would be many times as numerous as today.

The crux of the debate is whether to restore this system insofar as possible, or, to continue “management” practices that attack animal biodiversity by removing cattle, predators, prey or all three under various invasive species theories. For 150 years such efforts have steadily made things worse for the plants and animals they were meant to help.


NOTE: this post initially appeared on Horsetalk.co.nz on February 24, 2018. It was written by William E. Simpson II

Wild horses in the Owyhee herd management area in Nevada. © BLM


What will we do when the wild horses are no more? And what impact might that have on all the interdependent species and ecosystems, as well as domestic horses breeds?

That is a question that must be addressed if wild horses continue to be removed from the ranges essentially based upon how they look. Some wild horses who may appear ‘ugly’ on the outside to some, but may carry key genes that could be critical to the long-term survival of the equine species.

Science does not have all the answers today, and any such meddling by humans may result in a genetic bottleneck.

As far as preserving the very best wild horses, no man can do the same job that is accomplished by the continuous process of natural selection inside a natural ecosystem. There are hundreds of stressors that affect wild horses in the true wilderness that strengthen their genetic lines and none of those involves people who think they know which horses are the best.

Even if we applied extensive genetic testing of wild horses, we still know very little about which genes (and alleles) are responsible for resilience to a myriad of past, present and potentially fatal future diseases and environmental conditions.

Dr Ross MacPhee has already taken the Bureau of Land Management (BLM) to task over its management of wild horses. MacPhee, curator of vertebrates at the American Museum of Natural History, said in a speech on the 40th anniversary of the 1971 Wild Free-Roaming Horses & Burros Act: “What we are in now is a novel ecosystem; we’ve been altering it at an incredible rate for a very long period of time.”

In truly natural ecosystems, wild horses are subjected to myriad environmental and even social stresses within the herds and families, all of which over time determines which horses may survive and ultimately breed their strengths into the herd and genetic line.

Successful surviving wild horses have endured variations in forage, water quality and availability, viruses, bacteria, parasites, insects, temperature extremes, predators and competition between stallions for breeding rights to mares, just to name a few. And these genetically superior survivors must be left in the ecosystem and allowed to pass their genes into the gene pool of the wild herd. The removal and/or alteration of distribution of these surviving wild horses via any artificial means interferes with the natural evolutional processes at work that ensures the strength of the genetic lines of wild horses.

Loss of genetic diversity

A detailed study has already been undertaken that looked into the numerous breeds of domestic horses and the effects of inbreeding on heterozygosity. Generally, the overview of the findings suggests: “Not surprisingly, low diversity is observed in breeds with small census size, relatively old breeds with closed populations, and those with documented founder effects, whether due to population bottlenecks or selective breeding.“

The BLM continues to reduce herd sizes on all Herd Management Areas (HMAs). We already have a surprisingly low total US census that counted only 67,000 free roaming wild horses (according to the BLM), and likely significantly fewer than that highly disputed census number.

A wild horse foal near Farmington, New Mexico. © Kevin Kunkel, BLM New Mexico

In a report, wild horse advocate Marybeth Devlin said of the BLM’s Arbitrary Management Level (AML): “The maximum number of wild horses that BLM says the Western range can sustain – 26,715- is a political construct. Wild horses are few and far between. Per the 31,583,386 acres – 49,349 square miles -of dedicated wild-horse habitat across the Western states, the AML establishes a maximum stocking density of 1 wild horse per 1,182 acres – nearly 2 square miles. However, many herds are more severely restricted,” she said.

“To put this in perspective, nationally, BLM allows a stocking density of 1 cow-with-calf pair (or 5 sheep) per 76 acres, which means 8 cow-calf pairs (or 40 sheep) per square mile. Further, within dedicated wild-horse habitats – where the mustangs are, by law, supposed to receive principal benefit of resources -livestock are often awarded 90% or more of the grazing slots.”

Devlin said wild horses were not breeding out of control, and that the nominated annual herd-growth was at most 5%, meaning it would take 14 years for a wild horse herd to double. “Gregg, LeBlanc, and Johnston (2014) found the average birth rate across wild-horse herds to be just under 20%. But they also found that 50% of foals perish before their first birthday. Thus, the birth rate is just a temporary blip in the data. Starting with the surviving-foal rate (10%), and then subtracting a conservative estimate of adult-mortality (5%), the expected normative herd-growth rate would be, at most, 5%. At that rate, it would take 14 years for a wild-horse herd to double. The corresponding growth-rate for wild-burro herds is 2%. At that rate, it would take 35 years for a burro-herd to double.”

Devlin also said that she had noted that the BLM was reporting one-year increases in herd numbers “that are 50, 100, even 200 times the norm, far beyond what is biologically possible”.

For example, she said, “BLM claimed the Black Rock Range East’s population grew from 88 horses to 456 horses in one year, an increase of 368. If so, that would mean each filly and mare gave birth to 17 foals. BLM claimed the Carracas Mesa population grew from 12 horses to 75 horses in one year, an increase of 63. If so, that would mean each filly and mare gave birth to 21 foals.”

A BLM contractor’s helicopter musters wild horses during the fall 2016 Owyhee Complex roundup in Nevada. © Steve Paige.

She also said a report by Wild Horse Freedom Federation suggested that figures regarding the number of wild horses removed from the range and now boarded in private pastures did not appear to add up.

In many instances localized wild horse populations have been reduced to numbers that are no longer scientifically reasonable for the maintenance of critical genetic diversity within the population; some HMAs have fewer than 50 wild horses.

Further complicating and compounding this situation is the castration of wild stallions and the use of PZP as birth control on the mares in the remaining small and genetically limited wild horse populations.

As we learn in this article by Michael Ray Harris: “Independent research shows that PZP – which is derived from pig ovaries and is registered as a pesticide by the Environmental Protection Agency – can have lasting adverse effects on wild horses. According to Dr Cassandra Nuñez, PZP is associated with ovulation failure and can alter the birthing cycle of wild horses, resulting in birth out of season where the foal can die for lack of available food.

“Dr Nuñez also found that PZP has significant consequences on social behavior of wild horses. Normally bands of wild horses are very stable, and mares will stay with males for much, if not all, of their lives. However, when mares have been treated with PZP and cannot get pregnant, they may leave their bands. This creates instability in the bands and affects the health of the group members. The instability caused by PZP causes increased mortality, and can cause the parasite load of animals in the group to go up because of increased stress,” Harris wrote.

Pryor Mountain wild horses on the Montana-Wyoming border. © Brad Purdy, BLM Montana/ Dakotas

Breeding back to the core strength of the original genetic stock of wild horse gene-lines may ultimately provide the saving grace needed for many domestic horse breeds that are now suffering from a myriad of diseases and genetic conditions related to selective breeding.

Some wild horse advocacy organization keep doing the same old things and expecting new results. In the meantime, the American wild horse population trend-line is crashing. Statistically this is alarming. And this is also the reason why the BLM is adamantly opposed to American wild horses obtaining official ‘native species’ status under law, which if so obtained and based upon the current population census, would qualify them as an endangered species under the Endangered Species Act (ESA).

It seems our American wild horses are at greater risk today than at any time in their past history.

Please carefully research and consider what organizations you are supporting and what they are doing with your donation dollars. The very survival of our precious wild horses depends upon your love and good judgment.

Ranching, wildlife management, finance, oil & gas, real estate development and management.
  • I wondered if you are or is anyone pursuing the process of researching and adding wild horses to the endangered list? The number of people becoming aware not only the plight of our horses, but of the organizations who collect millions that are seemingly banking the money and doing little to actually stop the insanity, is growing. There is some interest in the endangered list, but honestly most of us have no clue where to start. Even available documentation from the BLM and DOI is hard to decipher and inconsistent with numbers of those left on ranges, the number in pens, the locations of pens, etc. I was asked this question. Pls note I am an amateur that is trying to spread the word. Thank you.

    • Hello Gloria,

      Wild horses have powerful advocates in there working for horses all the time. In my opinion the biggest problem wild horses face is that horse advocates will not allow them to be culled.

      Thanks for writing.

Leave a Reply

Your email address will not be published. Required fields are marked *