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Bison, cows and rabbits square off on Utah range

Study says jackrabbits, not bison, are cattle's main competitors in the Henry Mountains.

 

One day in 1941, 18 bison — 15 cows and three bulls — stepped from their wooden crates and wandered into Utah’s San Rafael Desert.

The shaggy beasts had been imported from Yellowstone National Park, a quixotic project co-sponsored by the state and a local rod and gun club. Seventy-four years later, those bison’s descendants find themselves unwitting combatants in a range war, blamed by Utah cattlemen for eating cows out of house and home. A new study, however, suggests that ranchers’ real beef should be with another mammal entirely — along with state predator control policies.

Upon their release in 1941, it didn’t take long for the bison to flourish. By the 1960s, the shaggy beasts had forsaken the desert in favor of the Henry Mountains, between Capitol Reef and Canyonlands National Parks, where their numbers kept growing; today, the population hovers at 325. While nearly all of America’s half-million bison contain cattle genes, the Henry Mountains herd has remained pure, its numbers carefully managed through the issue of wildly popular hunting tags. “We’ve worked hard to maintain a genetically viable population while increasing hunting and wildlife viewing,” says Bill Bates, section chief at the Utah Division of Wildlife.

Ranchers blame the Henry Mountain bison for competing with cows for forage — but a new study seems to exonerate the large herbivores. Photo courtesy of kyddyl.

Bison tend to attract controversy wherever they roam, however, and the Henry Mountains are no different. Unlike in Yellowstone, the problem isn’t that the bison harbor the bacterial disease brucellosis — the Henry herd has been certified clean since the 1960s — but rather that they compete with cows. Some 4,200 cattle share the bison’s winter range, and the struggle for forage can be fierce. When, in 2007, the state decided to incrementally grow the herd by dispensing fewer hunting licenses, many cattlemen were incensed. “The atmosphere was really intense,” says Utah State University ecologist Dustin Ranglack. “There was a lot of mistrust.”

With the state’s support, Ranglack set out to quantify just how much forage was being scarfed down by bison. “When you drive around that area, the bison are pretty conspicuous — they’ve trampled down the dirt, they’ve got these big dust wallows,” he says. “But when you step out of the truck, you start noticing the jackrabbit scat.” Ranglack saw clusters of little spherical pellets everywhere. He began to wonder whether rabbits might be even more prolific grazers than bison.  

To figure out who was eating what, Ranglack set up a simple experiment. At 20 sites throughout the Henry Mountains, he constructed two 8x8-foot squares of cattle-proof fencing — pens designed not to keep animals in, but to shut them out. To one exclosure at each site, he added an apron of chicken wire that deterred rabbits. In sum: 40 exclosures overall, 20 that barred cattle and bison but let rabbits in to browse, 20 that thwarted all grazers. To figure out which large herbivore was exerting more grazing pressure, he melded data from bison radio collars with ranchers’ own reports about their cattle’s activity.

A year later, Ranglack returned to his sites to see how much vegetation remained in each plot. According to his analysis, published Monday in the Journal of Applied Ecology, cows were the power mowers of the Henry Mountains, devouring around 52 percent of the available forage. Bison, by contrast, were eating just 13 percent. As for those tiny, innocuous jackrabbits and their lagomorph cousins? They gobbled 34 percent.     

Clearly, then, the Henry Mountains are chock-full of bunnies. But why? Ranglack speculates that Utah’s take-no-prisoners coyote management strategy is responsible for the rabbit explosion. The state spends $1.35 million on lethal coyote control annually, paying a $50 bounty for every kill; in the Henry Mountains, a trophy mule deer unit, at least 156 coyotes have been eliminated over the last five years.

Could Utah's aggressive coyote control policies be triggering an explosion in rabbit grazing rates? Photo courtesy of Franco Folini.

Ranglack is quick to point out that the link between predator policies and lagomorph populations hasn’t received scientific scrutiny. Still, it’s conceivable that, at least in some places, the trophic cascade set off by coyote control is actually costing Utah money in the form of lost cattle forage. And the state is taking notice: Ranglack’s study “is something we’ll definitely have to take into account” in devising future management plans, says the Division of Wildlife’s Bill Bates.

State managers aren’t the only folks rethinking the Henry Mountains ecosystem. Over a year ago, Ranglack presented his then-unpublished data before a group of local ranchers. He’d tried to keep cattlemen in the loop during his experiments, but he knew his analysis ran counter to expectations. He feared the meeting would turn ugly.

Nonetheless, Ranglack launched into his presentation, quickly arriving at the slide that broke down which critters were consuming how much grass. As he explained what he’d found, a loud, challenging voice boomed from the audience.

“Wait a minute,” the rancher interrupted. “You’re trying to say that jackrabbits are eating twice as much as bison?”

“That’s what I’m saying,” Ranglack replied. He waited nervously for the outburst. A murmur passed through the crowd. Then the rancher spoke up again.

“Well then,” he declared, “we need to stop shooting all these coyotes!” 

Ben Goldfarb is a Seattle-based correspondent for High Country News.