It has been 10 days since he killed here, but the smell of death still fills the air.

Pieces of the wild horse are left scattered among the dirt and grass. A red rib, not yet sun-bleached, lies in the dirt. A vertebra of spine over by a sage bush. Tufts of the horse’s dark mane sit among the black and brown lava rocks. Coyotes, vultures and bobcats have already been here, picking through the killer’s leftovers.

Less than 300 feet away, a herd of wild horses graze, unfazed by their proximity to the dismembered 10-month-old foal.

Prowling a home range of about 386 square miles is an adult male mountain lion known as M166. In the last year, while his feline counterparts have feasted mainly on deer, this cougar has garnered a reputation as a horse killer par excellence.

Local ranchers who believe this part of rural Modoc County has too many wild horses for the local ecology must, grudgingly, tip their hats to the mountain lion. They wish more of the area’s cougars had a gift for mowing down horses.

It might alleviate the messier issues that come whenever humans have to get involved.

“It’s kind of a split decision around here,” said Teri Brown, owner of the only feed store in town, Modoc Farm Supply. “A lot of people who have lived here their entire lives, they’ve never seen populations like this — both of horses and of mountain lions — and both make them uncomfortable.”

Wise examines the remains of a horse in Modoc National Forest. While M166's feline counterparts have feasted mainly on deer, this cougar has garnered a reputation as a horse killer par excellence. Kent Nishimura / Los Angeles Times

Wildlife biologist Colton Wise, from the Institute for Wildlife Studies, examines the remains of a horse possibly killed by a mountain lion, M166, who lives in Modoc National Forest. Kent Nishimura / Los Angeles Times

For the last few weeks, a helicopter has whirred above Modoc National Forest in an effort to gather 1,000 of the estimated 4,000 wild horses that live in the Devil’s Garden. Experts found that the 258,000 acres of the forest where the horses live can sustain no more than 402 horses without significant damage to the ecosystem and to the horses themselves. The effort has spawned complaints and lawsuits.

Even in a part of California with one of the densest cougar populations, M166 can only do so much. He has killed more than 30 horses since June of 2017. At the scene of one of the killings, he also killed a beaver. At another, a dove.

“This lion, he is just wired for horse,” said David Garcelon, president of the Institute for Wildlife Studies, which is collaring and researching cougars in Northern California. “It was one of those things where you go in the first time, and it’s ‘Oh my gosh, he’s taken a horse — look at this,’ and everyone is calling each other and you’re shooting pictures, and the next time, he’s taken two horses now, and pretty soon, you’re like ‘Everything he takes is a horse.’ One after another after another.”

Experts wowed by the mountain lion’s prowess at hunting horses say they only wish M166 was a she instead of a he.

“If it was a female, we’d be really excited because she’d be teaching her youngsters how to do that as well,” Garcelon said. “For a male, they come in do their business with their lady friend, and that’s usually the last of their involvement. It’s the female and what they feed on that helps the youngsters learn what they’re going to be killing and going after.”

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The plan to reduce the horse population has been controversial. It has led to multiple lawsuits by wild horse advocates who say the U.S. Forest Service is ignoring science in favor of cattle ranchers. Many argue that the forest should use fertility control on mares and, when needed, smaller gathers that use bait trap, instead of helicopter roundups.

“In the big picture, the Forest Service got here from a basic failure to manage the horses for years, and now they’re trying to deal with that, and they’re choosing the wrong path,” said Suzanne Roy, director of the American Wild Horse Campaign, which has sued over the management plan and the October gather. “These mass roundups are not only cruel — they also don’t work.”

Wild horses are chased by helicopter as they are gathered in the Devil's Garden section of Modoc National Forest. Experts found that the 258,000 acres of the forest where the horses live can sustain no more than 402 horses without significant damage to the ecosystem. Kent Nishimura / Los Angeles Times

Horse advocates say that the idea that the wild horses hurt the land ignores the thousands of cattle and sheep that graze on Modoc’s public lands every year.

Some argue that, instead of horse gathers, just let nature run its course — such as letting mountain lions take care of the problem.

As of Thursday, 713 wild horses had been removed from the Devil’s Garden Plateau Wild Horse Territory. Since the gather began in early October, 10 horses have been euthanized: eight for “preexisting conditions” and two for acute injuries. A foal died in holding last week. And two mares miscarried.

The most controversial aspect of the gather is forest officials’ decision to sell the horses 10 and older without limitations if they aren’t purchased or adopted by January at the earliest. Although it is against California law for horses to be sold for slaughter for human consumption, advocates fear the older horses could be taken elsewhere and killed. They could be sold for as little as $1, with a limit of 36 horses per buyer.

Modoc National Forest supervisor Amanda McAdams said she and her staff want to do everything they can to get horses adopted and avoid this option altogether. They’re holding the gather, she said, because they fear that if they don’t decrease the number of wild horses competing for foliage in the Devil’s Garden, many will suffer and die in the cold winter months.

“This is what I don’t think people understand — we love these horses,” McAdams said. “I feel like we’re doing the right thing, and the right thing is really controversial, and I understand why not everybody supports what we’re doing, and I appreciate what they’re saying and the way they feel, and I just hope they understand I’m doing the best I can. We’re doing the best we can.”

A wild horse, caught during gather operations, tries to escape while awaiting transport to a temporary holding facility, in the Devil's Garden section of the Modoc National Forest. Wild horses roam on the land of the Modoc National Forest. Wildlife biologist Colton Wise, from the Institute for Wildlife Studies, scours the ground for the remains of a horse potentially eaten by a mountain lion. Top: A wild horse, caught during gather operations, tries to escape while awaiting transport to a temporary holding facility in the Devil's Garden section of Modoc National Forest. Left: Wild horses roam in the national forest. Right: Wildlife biologist Colton Wise, from the Institute for Wildlife Studies, scours the ground for the remains of a horse potentially eaten by a mountain lion known as M166. (Kent Nishimura / Los Angeles Times)

M166 is doing the best he can to kill horses — about one per week. A husky cat, M166 has a strong jaw and thick neckline. When he was captured and collared, the puma weighed 138 pounds — similar in weight to an adult male St. Bernard.

He measured 7.25 feet from the tip of his nose to the end of his tail, a typical length for a male mountain lion.

His horse-killing canine teeth were a little longer than an inch, 30 millimeters long. At the time of capture, he had a chip out of his upper right canine, a tear in his right ear and some scars on his neck and left side.

No one knows where M166 was born — or how he learned to kill horses. But biologists have found that after a big cat dines equine, they’re less enthusiastic about cervine.

“Once they get a young horse, I think they realize, ‘Oh my gosh, this is way easier than a deer,’” said Meeghan Gray, a biology professor at Truckee Meadows Community College in Reno who has studied wild horses and mountain lions. “And so they tend to specialize.”

Male mountain lions will generally leave their mother’s territory, and they can travel significant distances. Two collared juvenile males in Northern California have traveled about 100 miles from their mother's territory.

All the horses M166 killed were younger than 14 months. The largest horse he is documented to have killed was about 350 pounds. Mustangs are generally on the smaller side of horses, usually weighing between 700 and 900 pounds. Larger wild horses might weigh 1,000 pounds. Their foals are much smaller, about 100 pounds or less.

M166 spends at least three days at a kill site, but acts as though he’s confident his food source will remain abundant: he usually eats a small part of the horse, maybe a haunch, before moving on.

This mountain lion, known as M166, lives in Modoc National Forest and mainly feeds off wild horses in the Devil's Garden. In this photo, he is just about to wake up and scamper off after being anesthetized so that wildlife biologists can record his vitals. Institute for Wildlife Studies

Because of this, M166 creates a food chain, leaving much of his kills for the coyotes, bobcats and vultures who readily swoop in when he leaves.

Beyond horses, his food options include deer, generally plentiful in Modoc, and pronghorn antelope. Pronghorn can see nearly 300 degrees around them without moving their head or eyes, and they can detect movement up to four miles away. They are also the fastest land mammals in North America, known to reach speeds of up to 60 mph.

And M166, evidently, does not like fast food.

By comparison, the mountain lions living in the Santa Monica Mountains and surrounding Southern California region kill mostly deer, eating the carcass for three to five days before leaving. They also kill goats and sheep if there’s no guard dog to scare them off.

“Whenever they make a kill, with deer, for example, they’ll go in right in the abdominal cavity, and they’ll eat the heart, the liver, all of that first,” said Jeff Sikich, a biologist with the National Park Service who studies mountain lions in the Santa Monica Mountains National Recreation Area. “They’ll push the stomach contents and intestines off to the side, they don’t consume that, and then they’ll go for the meat. That’s pretty typical cat behavior, in terms of how they feed.”

It’s unknown whether the removal of 1,000 horses from the Devil’s Garden will alter M166’s appetite.

Many in Modoc hope M166 doesn’t change.

“It’s just one mountain lion that we know of, and they say it is eating about one horse a week,” said Laura Snell, Modoc County director at UC Cooperative Extension. “But even at those numbers, we’re not even making a dent really at all in the population.”

A mountain lion is an apex predator, and its greatest threat, arguably, is humans.

To many, this is cattle country. In the spring, a cattle drive might cause a brief traffic jam, as a few ranchers who live close enough to public grazing lands in Modoc National Forest still use their method to move cows.

When a mountain lion kills livestock, it can be hunted down if the California Department of Fish and Wildlife issues a depredation permit. In 2017, three mountain lions were killed in Modoc County under these permits.

Fortunately for M166, cattle does not seem to be on the menu.

The mountain lion known as M166 stands over his most recent kill, a young horse. Even in a part of California with one of the densest cougar populations, M166 can only do so much. Institute for Wildlife Studies

jaclyn.cosgrove@latimes.com

@jaclyncosgrove

UPDATES:

1:30 p.m., Nov 2: This article was updated with the latest figures on the number of horses removed from the Devil’s Garden Plateau, the number euthanized and other statistics.

This article was originally published at 5 a.m. Oct. 29