New plan sparks concerns

Pryor Mountain Horse advocates worry about the future of a historic herd

At first glance, the Bureau of Land Management’s newly approved management plan for the Pryor Mountain Wild Horse Range doesn’t appear to make dramatic changes. The recommended herd size changes only modestly, and many of the management tools remain the same.

Look a little deeper, however, and a more complicated scientific debate begins to emerge.

The discussion is no longer simply about how many horses should live in the Pryor Mountains. It has become a debate over genetics, ecology, population biology and whether the management decisions made over the next decade will preserve one of America’s most historically significant wild horse herds.

After nearly six years of study, public comment and environmental review, the BLM and the U.S. Forest Service have adopted a new Joint Herd Management Area Plan that will guide management of the herd for roughly the next 10 years. The agencies say the plan is designed to balance wild horses with available forage, water resources, wildlife habitat and overall rangeland health while complying with previous federal court rulings.

“This joint plan is a critical step in ensuring the long-term health of both the rangeland and herd,” BLM Billings Field Manager Nate Arave said in announcing the decision. “By using the best available science and a collaborative inter-agency approach, we are creating a sustainable future that protects these horses while maintaining the integrity of the ecosystem.”

The revised Herd Management Area Plan establishes an Appropriate Management Level (herd size) of 107-120. It intends to conduct an initial gathering to reduce the herd to approximately 150 horses before making additional removals “as expeditiously as possible” until the population reaches the lower end of the approved management level of 107.

Nancy Cerroni, Executive Director of the Pryor Mountain Wild Mustang Center, addressed the plan, “At first glance, that range of 107-120 does not appear dramatically different from previous management levels,” she said. “The more significant question is how the BLM intends to manage the herd to reach and maintain that population.” 

MORE THAN SIMPLY REMOVING HORSES

Many people assume herd management simply means periodically rounding up horses. In reality, the population changes every year through both natural events and human intervention.

Nature also plays a significant role in regulating the herd. Horses die from old age, disease, accidents and predation, with foals experiencing the highest mortality rates. Cerroni said mountain lions have been responsible for an unusually high number of foal deaths during the past three years.

Human management primarily relies on two tools.

The first is fertility control, which reduces the number of foals born each year. The second is selective removals, in which horses are gathered from the range and transported to holding facilities. Most eventually become available for adoption, while some are later offered for sale. In limited situations, the BLM may euthanize horses for humane reasons, although that is not the primary method used to reduce herd numbers.

For Cerroni, however, the critical question is not simply how many horses leave the mountain, but which horses leave.

THE SCIENCE OF SMALL POPULATIONS

From a biology standpoint, herd size affects much more than the number of horses visitors see.

“One of my principal concerns with the reduced population is maintaining the long-term health and resilience of the herd,” Cerroni said. “Herd size affects much more than the number of horses on the range. It also influences age structure, family representation, genetic diversity and the long-term continuity of the herd.”

Population biologists often refer to unpredictable events such as drought, severe winters, wildfire and disease outbreaks as stochastic events. Larger populations generally recover from those events more easily because they contain greater genetic diversity and more breeding animals.

Smaller populations, particularly geographically isolated ones like the Pryor Mountain herd, have fewer biological safeguards.

“A larger, genetically diverse population is generally better able to withstand these unexpected challenges,” Cerroni said. “For a geographically isolated herd with the unique history of the Pryor Mountain horses, maintaining sufficient resilience for future generations is just as important as managing current population numbers.”

WHICH HORSES STAY?

The revised Herd Management Area Plan establishes a management goal of maintaining a level of genetic diversity sufficient to avoid inbreeding depression while also maintaining characteristics typical of Pryor Mountain horses of mixed ancestry, including Colonial Spanish influence. The BLM states that selective removals will be one of the primary tools used to accomplish those objectives.

Those removals follow a detailed list of criteria.

Managers first remove horses with inherited genetic defects such as dwarfism, clubfoot or contracted tendons. Horses resulting from close inbreeding also become priorities for removal. Managers then focus on achieving desired age classes and sex ratios, generally removing younger horses before older animals. Mares that have not responded to fertility control treatments may also be selected, while coat color is considered only after those other factors have been addressed.

Cerroni believes one important consideration is missing.

“Notice that the selective removal criteria say nothing about how the BLM intends to maintain the characteristics typical of Pryor Mountain horses, despite that being one of the stated management goals.” she said.

She agrees that the plan addresses overall genetic health by removing horses with inherited defects and reducing inbreeding, but believes preserving the Pryor herd requires something more.

“Maintaining genetic integrity involves more than preserving overall genetic diversity,” she said. “The preservation of the unique characteristics of the Pryor Mountain horses is a different but equally important management objective.”

That distinction may sound subtle, but genetically it represents two different management philosophies.

One management philosophy focuses on maintaining healthy levels of genetic diversity across the entire population. The other emphasizes preserving the distinctive characteristics that have historically defined the Pryor Mountain herd. Cerroni believes the remaining question is how the BLM intends to implement that second objective. While the plan identifies preserving characteristics typical of the Pryor Mountain horses as a goal, it does not clearly explain how the selected management framework will accomplish that objective over time.

A NATIONALLY RECOGNIZED HERD

The Pryor Mountain horses are not famous simply because they are wild.

They are among the most extensively studied wild horse herds in the United States. Genetic studies have consistently identified a significant Colonial Spanish influence within the Pryor Mountain herd despite occasional introductions of other horse bloodlines.

Research, such as that done by the Mustang Center, has documented family bands, maternal lineages and reproductive histories for decades, creating one of the most complete genealogical records of any wild horse herd in America.

“One of the unique strengths of the Pryor Mountain herd is that we know far more about individual horses and family relationships than is known for most wild horse populations,” Cerroni said.

She believes that information provides managers with an unusual opportunity to make highly informed decisions about which horses remain on the mountain.

“The plan describes several management tools, including fertility control and selective removals, but it does not clearly explain how those tools will preserve the distinctive characteristics and long-recognized Colonial Spanish influence over time,” she said.

SCIENCE AND TRANSPARENCY

Cerroni is careful to say her concerns are not about whether science should guide management.

“I believe the BLM relied on a great deal of scientific information, and I certainly support using science to guide management decisions,” she said.

Instead, she questions whether the appropriate scientific data were applied to every aspect of the analysis.

She notes that the BLM’s own handbook recommends using several years of annual monitoring data, including forage production, precipitation and utilization, when calculating an Appropriate Management Level because environmental conditions naturally fluctuate from year to year. 

The revised management plan was developed in response to previous federal court rulings requiring the BLM to revisit questions involving genetics and appropriate management levels. Cerroni says whether the agency has fully answered those questions remains uncertain and is one reason the Pryor Mountain Wild Mustang Center has appealed the Decision Record.

MORE THAN HORSES

The scientific debate also has local consequences.

Every summer photographers, wildlife enthusiasts, historians and tourists travel to the Pryor Mountains hoping to observe individual horses and family bands that many have followed for years through books, documentaries and online updates.

“The Pryor Mountain herd is not just another wild horse herd,” Cerroni said. “It is one of the most documented wild horse herds in the country and has deep historical, genetic, educational and community significance.”

She worries that as the population becomes smaller, visitors may lose some of the unique experience that has made the Pryor herd famous.

“People do not come here simply to see a horse,’” Cerroni said. “They come to experience the Pryor Mountain herd, with its history, relationships and unique character. That is what we hope future management will continue to protect.”

For communities like Lovell, the debate extends beyond biology. The Pryor Mountain horses attract visitors who fill hotel rooms, buy fuel, eat in local restaurants and spend time exploring the Big Horn Basin.

Whether the new management plan ultimately succeeds will likely be measured by more than simply counting horses. Over the coming decade, managers, scientists and horse advocates will all be watching a more difficult question: can one of America’s most significant wild horse herds remain both biologically healthy and historically unique at the same time?