Editor’s note Nov. 26: This article was updated to clarify that the study refers to “wild horses” as “free-roaming horses,” further explain the Bureau of Land Management’s target populations for free-roaming horse herds and clarify some of the study’s terms.
When Jeff Beck released his research linking free-roaming horse overpopulation to the decline of sage grouse, some went so far as to call it “malpractice.”
“It was conducted under rigorous scientific protocols,” Beck said, who’s also a University of Wyoming (UW) professor of wildlife habitat restoration ecology. “It passed the muster of peer review to be published in a well respected scientific journal.”
Beck’s study was published this fall in the Journal of Wildlife Management. It found that in areas where free-roaming horses were more abundant than population targets, survival rates for sage grouse nests, broods and juveniles dropped anywhere from 8 to 18 percent. Beck said the problem is exacerbated by management efforts not keeping pace with free-roaming horses repopulating.
But wild horse advocates said the onus isn’t all on the horses – livestock should’ve been a factor. WyoFile initially reported on the study, and on their Facebook post there’s 750 comments, many critiquing it.
“Grazing by cattle is such a major factor in sage grouse habitat quality that livestock grazing was found to be a significant threat to the species when they were found warranted for listing by USFWS (U.S. Fish and Wildlife Service) in 2010,” said Executive Director of the Western Watershed Project Erik Molvar, who went on to write an opinion piece about this in Wyofile. “It is scientific malpractice - and demonstrates deliberate bias - to exclude this factor from the model.”
But Beck said this is simply untrue. Livestock were factored in, just not directly, to his study.
“We use the BLM numbers,” Beck said, referencing the Bureau of Land Management’s target population range for each free-roaming horse herd, which takes into account how many animals the landscape can support, including livestock and wildlife grazing. Beck then compared the BLM’s estimates for the size of each herd, compared to the upper population target, to measure horse impacts. “We’re showing that once the number of horses are above what the BLM wants to manage, that's when you have a problem.”
Beck said his team narrowed the focus to free-roaming horses because that was the species that consistently exceeded the BLM’s management targets. He added that in some areas, horse numbers are three times or more than what the BLM thinks the landscape can support.
“In practice overgrazing in these areas is a result of overabundant free-roaming horses,” according to the study.
Basically, Beck said you have to trust BLM data to support his study.
In over 15 years of research, he found time and time again – population matters.
“When horses get too high, they impact sage grouse,” he said.
Beck’s team used GPS transmitters to monitor 1,000 sage grouse in central and southern Wyoming, both in landscapes with free-roaming horses and without.
In areas where horses were above population goals – up to three times as much – they found about an 8 percent decrease in survival for sage grouse nests. For sage grouse broods of chicks and juveniles, their likeliness to survive dropped 18 percent.
There was no correlation with adult female sage grouse. Beck said this might be because of how free-roaming horses impact the landscape.
“They increase bare ground, and they also change the grass composition to those grasses that are shorter in height,” he said. “So if you think about a sage grouse nest or broods, they're more exposed to the elements, as well as to predation.”
Beck said the study could be a valuable tool for land and wildlife managers.
Sage grouse have steadily declined across the West since the ‘60s, and there’s a lot of efforts to reverse that. This includes limits on energy development in critical sage grouse habitat. Wyoming and the federal government are currently in talks about an updated plan.
The main goal that most agree on is keeping the bird off the Endangered Species List. Beck said understanding that free-roaming horses are a part of the puzzle could help.
“There's so many threats to sage grouse populations, and one that we haven't looked at very much is the effect of horses,” Beck said.
He emphasized that finding ways to bring populations down to the BLM’s set numbers is key. Beck said this is another point of misunderstanding about his research among wild horse advocates.
“There's no way that our research was suggesting to remove all horses. That's just an incorrect, off the hip idea,” Beck said. “Our research actually showed if horses are maintained so they don't exceed that [BLM maximum target] level, then that will be much more harmonious with the sage grouse population. The two species can coincide in the same location.”
The BLM held several wild horse roundups this year in three herd management areas in Wyoming. In the Lander area, 2,577 horses were gathered, bringing herd numbers in line with the BLM’s population goal that peaks at 536. In the Cody area, 90 horses were gathered to align the herd with the 70 to 140 horse management level. In the Rock Springs area, 536 were gathered, bringing the herd to the lower end of the goal population range, which is 205.
