Study implicates wild horses in greater sage-grouse population decline

Study implicates wild horses in greater sage-grouse population decline
Greater Sage-Grouse

RENO–The U.S. Geological Survey (USGS) on Monday released a study that is certain to stir controversy. It explores the relationship between two symbols of the American West: federally protected wild and free-roaming horses and greater sage-grouse.

According to a USGS report released on March 30, “greater sage-grouse populations have declined significantly over the last six decades, with an 80% range-wide decline since 1965 and a nearly 40% decline since 2002.” 

The study paints a David versus Goliath picture of the relationship between the two animals. It indicates that greater sage-grouse populations may continue to decline–by more than 70% within areas where the horses live by 2034–if horse populations continue increasing at current rates.

The Bureau of Land Management (BLM) has laid out what it calls “appropriate management levels” (AMLs) to balance use of rangelands by horses, livestock and wildlife.

The USGS reported that a related analysis found “that for every 50% increase in horse abundance over an AML, sage-grouse abundance is likely to decline by 2.6%. When horse populations are double the established AML, for example, there is a 76% probability of sage-grouse decline. This has important implications for parts of Nevada, where horse populations are more than four times higher than the AML set by the BLM for that area.”

Reducing horse numbers could neutralize the negative impacts, according to the study.

The study indicates impacts to sage-grouse population trends in areas where horse numbers are at—or below—established AMLs are consistent with areas where horses are altogether absent.

“This suggests that the maximum AMLs are effective at neutralizing the adverse impacts that horse populations have on sage-grouse populations and that free-roaming horses have the potential to coexist with native wildlife under the right management approach,” reads a press release attached to the study.

According to the BLM, the appropriate number of wild horses and burros for rangelands spanning 10 Western states is just shy of 27,000. The agency estimates that as of March 2021 there were about 72,000 wild horses on federal lands and 14,000 burros for a total of more than 86,000.

More than half of them, some 47,000, are in Nevada.

Wild horses from the Fish Creek Herd Management Area near Eureka, Nevada.
Wild horses from the Fish Creek Herd Management Area near Eureka, Nevada. Image: BLM

Advocates dispute impacts of wild horses

Wild horse advocates argue that the land could support many more wild horses and burros were it not for grazing permits issued to cattle ranchers. 

A 2019 documentary entitled Horse Rich & Dirt Poor stoked dispute between advocates of wild horses and members of the cattle ranching industry. Horse advocates said the documentary scapegoated wild horses for rangeland problems while ignoring the contributions of cattle to

rangeland degradation. 

Ranchers, on the other hand, say cattle on public lands are managed as part of their grazing leases, management practices that do not apply to free-roaming horses 

The federal grazing fee for 2021, announced in January, is $1.35 per animal unit month (AUM) for public lands administered by the BLM and the same for lands managed by the U.S. Department of Agriculture Forest Service. The 2020 public land grazing fee was the same.

Nevada administers 668 grazing authorizations on 797 grazing allotments and has the most public land authorized for grazing by the bureau—about 43 million acres. The state permits about 2 million AUMs.

The USGS reported that older research indicated sage-grouse have experienced substantial population declines within the arid sagebrush environments due to steady and continued habitat loss that is due only in part to wild horses. Wildfires and other disturbances to sagebrush habitat also play a role in the bird’s declining numbers.

“While this study highlights the challenges of maintaining biodiversity in sagebrush environments, it also provides valuable insights into the options for wildlife management,” said David Applegate, USGS associate director. “It’s an example of how the USGS provides landscape-scale science and data about resource conditions, trends and interactions that state and federal wildlife managers can trust to help make informed and effective decisions.”

The study is likely to draw criticism from wild horse advocates for its assertion that wild horses are descended from domesticated horses introduced to the United States during the 16th and 17th centuries.

Wild horse advocates contend that horses were native to the Americas and their frequent designation as an invasive wildlife species is spurious.

“Modern science, especially DNA testing, contradicts this myth,” contends horse advocate and author Terri Farley. “Paleolithic horses and modern equines share the same DNA.”

USGS officials say that preserving the integrity of sagebrush ecosystems in the American West within the paradigm of multiple-use is a common goal of management agencies tasked with public lands stewardship.

“The results of the study indicate that coexistence is possible for free-roaming horses and sage-grouse if horse populations are maintained below established AMLs,” said Peter Coates, a research wildlife biologist with the USGS Western Ecological Research Center and lead author of the study.

More details can be found in the study.