Wild horse management and conservation is one of the most politically charged issues on the federal public lands, and it is critically important to have objective, unbiased research to help inform the policy debate. The recent University of Wyoming study led by Jeffrey Beck on sage grouse and wild horses doesn’t live up to this standard. Most glaringly, the study fails to consider the impacts of cattle and sheep on sage grouse.
Opinion
The study made no attempt to measure wild horse population density per square mile, which would be the objective measure of horse impact on sage grouse habitat. Instead, it used percentages of politically influenced Bureau of Land Management population targets called “appropriate management levels,” which vary widely from area to area. It’s like setting an arbitrary population target of 20,000 people in Laramie, then calling Laramie “overpopulated” at 30,000 residents, and then comparing that level of human impact to Rawlins with a population of 8,200 and an arbitrary target set at 5,470. That puts both towns 50% over their population targets, but the targets themselves are arbitrary. Clearly, human impacts in the two towns are different. That’s one critical flaw in the study.
But let’s get to the biggest flaw: failure to consider the effects of cattle and sheep.
Cattle and sheep impacts on sage grouse habitats are well-established, and these impacts were identified as a principal threat to the species when sage grouse were found warranted for listing in 2010. When grazers — cattle and sheep are typically authorized to graze 50 to 65% of the annual forage production — reduce grass height below 7 inches, sage grouse are more exposed to predators and their camouflage is less effective, resulting in reduced nest success. When grazing gets so heavy that native perennial bunchgrasses are suppressed, cheatgrass can invade the disturbed landscape, resulting in a loss of forbs and poor habitat quality, and fires that wipe out the sagebrush.
Peter Coates of the U.S. Geological Survey co-authored the Beck paper, and its methods mirror a 2021 study that Coates and others did in Nevada and northeast California. In that study, like this one, Coates cast wild horse “overpopulation” as the degree to which wild horse populations exceeded arbitrary appropriate management level targets set by agency bureaucrats, a level the National Academies of Science found to have no scientific basis. Coates failed to include domestic livestock grazing in the model, even though livestock grazing has consistently been found to be a key variable affecting sage grouse habitat quality.
Coates, when presenting his 2021 findings at a webinar, was explicitly questioned on why grazing impacts by cattle and sheep were excluded from the model. His response to the question treated livestock grazing as part of the baseline on western public lands, while the impacts of wild horses are “extra grazing on the landscape aside from cattle grazing.” In other words, domestic livestock are an integral part of sage grouse habitat, so their effect on bird populations can be ignored.
It’s an outrageous assertion that exposes an extreme level of scientific bias.
Wild horse impacts on sage grouse habitats are intertwined with livestock grazing and with those of every other wild herbivore. The only way to tease them apart is with rigorous hypothesis testing that offers both livestock and wild horse densities to the model, comparing the relative influence of each on sage grouse populations. Doing so would answer three key questions. Do wild horses have the primary impact on sage grouse numbers? Or do cattle and sheep have the primary impact on sage grouse numbers? How do the impacts of wild horses and livestock on sage grouse compare? The failure of these researchers to ask the right questions, and to tease apart the impacts of the different herbivores in question, suggests that they didn’t want to know the answer.
The Bureau of Land Management sets how many livestock it authorizes for each lease parcel annually and publishes wild horse population estimates each spring. Access to information is not the problem. It’s industry sway over management decisions.
The Bureau of Land Management is responsible for managing sage grouse habitats and regulates livestock numbers and wild horses alike. If wild horse numbers climb above herd targets, the agency has full legal authority — under 43 CFR § 4710.5 — to close wild horse Herd Management Areas to domestic livestock, temporarily or permanently, to compensate. Grazing permits also include terms that allow the Bureau of Land Management to end livestock grazing when forage starts getting scarce or land health problems emerge. Such adjustments would lessen combined habitat impacts on sage grouse, and all other species. Yet, we rarely see the agency do this. Clearly, the Bureau cares more about keeping the livestock industry happy than it does about maintaining viable sage grouse populations, and it appears that the University of Wyoming is complicit in scapegoating horses as a means to sidestep the hard truths about cattle.
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