National Parks Traveler

Do Yellowstone bison need ESA protection?/NPS file, Jim Peaco

Putting Bison Genetics Under The Microscope At Yellowstone

By Kurt Repanshek

It was not quite 120 years ago when Charles "Buffalo" Jones got his wish, that being to have the federal government support his work to keep bison from being killed off the face of the Earth. His wish was granted in July of 1902 when Jones, a somewhat eccentric cowboy who once thought he could boost the musk ox population by moving a dozen or so from Canada's cold and snowy northlands to an island off the California coast for breeding, was hired to be Yellowstone National Park's game warden.

At the time, there were only about 25 bison left in Yellowstone, a small herd that escaped the "great slaughter" that reduced North America's bison from perhaps 60 million when Columbus reached the new world to a few hundred or so by the end of the 19th century. Yellowstone's small herd at the time represented what is considered to be the only wild bison that avoided the slaughter, and they did that by retreating deep into the park's interior.

Jones realized that such a small herd risked genetic inbreeding problems, and one of the first things he did was reach out to ranchers who had established private herds. He obtained three bulls from Charles Goodnight in Texas, who gained fame driving cattle along the Goodnight-Loving Trail from Texas north to Wyoming, and another 18 from a herd in northern Montana that two men managed near today's Glacier National Park.

By the end of his first year on the job in Yellowstone the cowboy had raised the bison population by a dozen, and in 1907, two years after Jones lost his job, the park's growing bison herd was moved from a pasture near Mammoth Hot Springs to the Lamar Valley, today home of the famed buffalo ranch, or at least its history. By 1936, bison ranching was going so well in the park that there were nearly 650 individuals at the ranch. Thirty-five were then let loose in the Firehole Valley, and another 36 were released into the Hayden Valley.

Jones is just a footnote in the national park's history, but his work might have played a role in a current legal drama revolving around whether Yellowstone bison are an endangered species and, if so, are there two genetically distinct herds in the park and should those bison be managed for more than 6,000 animals vs. the 5,000 or so currently roaming the park?

Do Yellowstone's Bison Need ESA Protection?

Today, Yellowstone's free-roaming bison are believed to be genetically pure because they descended from pocket herds that escaped the great slaughter of the late 19th century as they were secreted away in the upper headwaters of the Yellowstone River deep in the park's interior. Because of that, some believe the park's herd needs protection under the Endangered Species Act from a range of threats, such as disease, habitat loss, climate change and accidental introgression of cattle genes.

Back in 2014, the Buffalo Field Campaign and Western Watersheds Project petitioned the U.S. Fish and Wildlife Service to extend "threatened" or "endangered" designation under the ESA to Yellowstone's bison. In a somewhat lengthy petition of more than 60 pages, the group and the Western Watersheds Project argued that Yellowstone's bison are "the largest remnant population of the Plains bison that ranged across much of United States until it was eliminated post-settlement."

But the Fish and Wildlife Service opted in December 2015 not to extend such protection, holding that there was no "substantial scientific or commercial information" to justify such a designation and that bison numbers in the park were growing, and so it wasn't going to do a "status review" on whether bison were doomed. In its formal decision, the agency also noted that "[S]ince individuals from other herds were used to supplement the YNP bison in 1902 [thanks to Buffalo Jones-ed.], estimates suggest only approximately 30-40 percent of the YNP bison genetic makeup derive from the original 25 survivors. Thus, maintenance of subpopulation genetic differentiation and overall genetic diversity may not be crucial for preserving genes from the survivors of the historic bottleneck."

That point, that there might not be "subpopulation genetic differentiation," was the bone of contention for the Buffalo Field Campaign and Western Watersheds Project, who found a study suggesting that Yellowstone's "central" and "northern" bison herds are two separate herds that are "genetically distinct" and so should be preserved.

Bison along the Firehole River/NPS file, Jacob W. Frank

Key to their argument is that while the Interagency Bison Management Plan adopted in 2000 was established to manage Yellowstone bison, it "was inadequate, in part because it (1) was primarily designed to protect against brucellosis—which, the Petition contends, is not nearly as significant a threat from bison-to-cattle transmission as the IBMP claims—rather than to ensure the survival of the bison, and (2) fails to account for the two distinct genetic herds when setting a population target and thus sets too low a population target to ensure the genetic survival of both herds (and thereby the entire population)."

Well, it took more than two years, but a federal judge early in 2018 disagreed with the Service.

"The Service argues that ultimately, Buffalo Field’s concern over the (park's) two subpopulations is irrelevant because the bison population is growing," wrote U.S. District Judge Christopher R. Cooper. "The Service may have a point, and on remand the Service may well be able to reach the same outcome after applying the proper standard. But to do so, the Service must explain why the evidence supporting the petition is unreliable, irrelevant, or otherwise unreasonable to credit rather than simply pick and choose between contradictory scientific studies."

Judge Cooper in his ruling cited two opposing scientific positions on the question of whether the park's central and northern bison herds are separate, and wrote that "if reasonable scientists disagree -- and one of those positions would indicate listing is warranted -- a reasonable person could choose to agree with the scientist who supports the petition and, as a result, that listing may be warranted."

"Unless the Service explains why the scientific studies that the petition cites are unreliable, irrelevant, or otherwise unreasonable to credit," the judge added, "the Service must credit the evidence presented."

The study in question was by Dr. Natalie Halbert, who theorized that the two herds are genetically distinct. Digging into her study, Judge Cooper wrote that the IBMP's population goal of 3,000 bison in Yellowstone could be too low to support two genetically distinct herds.

"Since other studies have suggested that around 3,000 bison are needed to ensure a herd’s survival, this suggests that the 3,000 bison population target for both herds is too low to ensure that each herd will survive," he noted.

Well, the Fish and Wildlife Service took another look at the matter ... and again declined to extend ESA protection to Yellowstone's bison.

In September 2019, the Service said, "the petitions do not present substantial scientific or commercial information indicating the petitioned action may be warranted for Yellowstone National Park bison. Because the petitions do not present substantial information indicating that listing Yellowstone National Park bison may be warranted, we are not initiating a status review of this species in response to the petitions."

Swing And Another Miss

Again the Buffalo Field Campaign appealed that ruling, and again a judge ruled against the Service. In his ruling [attached below] earlier this month, U.S. District Judge Randolph D. Moss wrote that the Service "once again, failed to credit the Halbert study and, once again, relied on an (arguably) conflicting study without offering a reasoned explanation for that choice."

"It is, of course, possible that the Halbert study is flawed in a material respect. It is possible that its data are outdated and that the tipping point in mixing between the central and northern herds occurred in the short window between when the data were collected for that study and when the data were collected for the Forgacs study. It is possible that mitochondrial DNA is more important than nuclear DNA in measuring genetic divergence. It is possible that the Hedrick [population] study either overestimated the [Minimum Viable Population] for Yellowstone bison or that its analysis does not extend to subpopulations," continued Moss. "And perhaps the Service not only accepted one or more of these possibilities but, also, rationally concluded that the question was sufficiently open-and-shut that it could, and should, be resolved at the 90-day stage. But the Court can defer to an agency’s scientific judgment only if the agency’s rationale 'may reasonably be discerned,' and the 2019 finding says none of this. Just as the Court may not substitute its scientific judgment for that of an expert agency, it may not guess at what the agency might have intended or might say on (yet another) remand."

While Moss did not rule one way or another on whether Yellowstone's bison merit ESA protection, he did say the Fish and Wildlife Service needs to do a better job of explaining why it doesn't think they do. He also expressed some consternation that a case brought in 2014 has not been satisfactorily handled by the agency.

"Although the Service has twice failed to employ the correct the evidentiary standard in reviewing the long-pending petitions, there is no reason to believe that the agency is acting in bad faith or that it is unprepared to adhere to the Court’s decision," the judge wrote. "It is concerning, to be sure, that over seven years have now passed since the 2014 petition was filed. But it remains unclear whether sufficient basis exists to proceed to the next stage of the ESA process, and, in light of the substantial amount of work done to date, the Service should be able to answer that question promptly."