Wolves killed another two cattle Aug. 22-23 near Fort Klamath in Southern Oregon, the latest in a string of attacks that has prompted nightly patrols of the vast grassy range.

That makes 11 confirmed depredations since May — including six in August — all of which were attributed to the Rogue pack.

Roblyn Brown, wolf program coordinator for the Oregon Department of Fish and Wildlife, said it is the worst spate of wolf-livestock conflict in Oregon since the Imnaha pack had 21 confirmed depredations between 2010 and 2011 in the Upper Wallowa Valley.

But unlike that situation, stray bone piles and animal carcasses are not to blame for attracting wolves. Brown said she does not know what is causing the pack to target cattle so frequently.

“We’re not really able to see the world the way they do,” Brown said.

The Rogue pack has repeatedly preyed on yearling steers in the Wood River Valley between Klamath Falls and Crater Lake National Park, on the east side of the Cascade Range. The area is highly productive ground for summer grazing, with sprawling pastures that range from 300 to 700 acres and 400 to 900 steers per pasture.

Wolves are still listed as a federally endangered species west of highways 395, 78 and 95, meaning ranchers and land managers can only use non-lethal deterrents to protect livestock.

Beginning in July, Brown said staff from ODFW, the U.S. Fish and Wildlife Service and USDA Wildlife Services have taken turns driving around the valley every night, listening for howling and signs of wolf activity. If they catch wolves on pastures, they can haze and harass the predators back into the mountains.

Human presence is about the only effective tool at their disposal, Brown said. Because the pastures are so large, it is not possible to hang fladry along the fence lines that can stretch for several miles.

ODFW does not have a working GPS tracking collar on any member of the Rogue pack, Brown said. Even if they did, the sheer size of the area also makes it difficult to use things like radio-activated alarms and flashing lights to scare off wolves, which are far more effective in smaller paddocks closer to homes.

“We’re still going to have to rely upon human presence to scare off even a collared wolf,” Brown said.

Brown said the agencies are working to collar a member of the Rogue pack, and are in “constant communication” with ranchers in the area who are following the rules and taking necessary steps to prevent further attacks.

”They’re doing a great job now about cleaning up their carcasses quickly, and burying them quickly,” Brown said. “They’re also going out at night.”

The Trump administration is still considering whether to delist wolves across the Lower 48 states. Delisting would allow ODFW to consider killing wolves in limited circumstances that repeatedly attack livestock — a standard known as “chronic depredation” under the state’s wolf management plan.

Butch Wampler, who oversees grazing at Nicholson Ranch near Fort Klamath, said they have lost two yearling steers to the Rogue pack this year. The ranch leases approximately 960 acres for 1,250 cattle brought up from Detar Livestock in Dixon, Calif.

Wampler also spotted three wolves through his binoculars leaving the scene of the kill that happened the morning of Aug. 23 on a neighbor’s property. Attacks have continued even with the increased nightly human presence, he said, leaving ranchers frustrated.

“All you can do is watch them go away. You can’t protect the livestock that you’re here to take care of,” Wampler said. “I think (delisting) is the only way you can get a handle on them. They’re not going to quit. They’ve proven that over the last month.”

Environmental groups, however, oppose delisting. Zoe Hanley, Northwest representative of Defenders of Wildlife based in White Salmon, Wash., acknowledged problems with the Rogue pack but said there is an opportunity for wolves and humans to coexist on the landscape.

Delisting is premature, Hanley said, arguing there are still large areas of suitable habitat where wolves have not fully recovered, including significant portions of the Pacific Northwest.

“The critical thing to keep in mind is killing wolves is a short-term Band-Aid, not a long-term strategy to reduce wolf-livestock conflicts. It is better to work toward long-term strategies such as strategic grazing practices with the targeted use of non-lethal tools to empower ranchers to share the landscape with this native carnivore.”

Brown, ODFW’s wolf program coordinator, said a combination of non-lethal tools and preventive measures such as cleaning bone piles are important even in areas where wolves are not yet present.

”That prevention is huge,” she said. “And it can stop predation from happening in the first place.”