Mountain lions have major ecological impact even in small preserve

 

Peer-Reviewed Publication

Stanford University

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A mountain lion photographed by a motion-activated cameras on Stanford's Jasper Ridge Biological Preserve.

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Credit: Image courtesy of Trevor Hébert/Stanford University.

Big cats have a big impact. A long-term study showed that when mountain lions began regular visits to a small, suburban preserve about 45 miles south of San Francisco, it changed the behavior of many other animals.

Mountain lions (Puma concolor) started appearing with increasing frequency on trail cameras at Stanford’s Jasper Ridge Biological Preserve ('Ootchamin 'Ooyakma) from 2015 to 2020. Researchers documented a corresponding drop in deer activity compared to the prior years of lower or absent puma activity. Vegetation surveys also showed that many woody plants deer like to eat or tend to trample, including young oak trees, began to thrive.

These types of multi-level effects, called trophic cascades, have been studied primarily in large wilderness areas, particularly cascades caused by apex predators such as wolves reintroduced into Yellowstone National Park. This research, published in Ecology and Evolution, indicates the effect can be found in smaller preserves as well.

“In the past, small preserves like Jasper Ridge have often been dismissed for holding very little ecological value, but this study shows that when these small preserves are connected to large wilderness like the Santa Cruz Mountains, you can still see magnificent ecological phenomena like trophic cascades,” said Chinmay Sonawane, the study’s first author and doctoral student in biology in Stanford’s School of Humanities and Sciences (H&S). “They are not just things that happen in places like Yellowstone far away from the city and people. They can happen in these places that are quite small and more urban as well.”

The ecology of fear
The researchers analyzed data frommotion-activated cameras and vegetation surveys and found two types of trophic cascades, one that connected mountain lions, deer, and vegetation, called a tri-trophic cascade, and another that involved smaller predators at Jasper Ridge. For the second, increased puma presence was associated with decreases in the activity of coyotes and bobcats, which were perhaps leaving the area or changing the time they are active to avoid the much larger pumas.

With fewer coyotes and bobcats on the landscape, foxes appear to have seized an opening and were seen more often, which then may have suppressed the activity of their primary prey: rabbits.

These patterns involving an apex predator have been called the “ecology of fear,” since the mere perception of a large predator can cause other animals to change their behavior, which then affects the other organisms that they rely on for food.

In this study, the findings at the lower level of the cascades – the indirect influence of mountain lions on vegetation, foxes, and rabbits – are considered provisional, as other influences such as changes in fog and temperature could not be ruled out.

Yet the mountain lion presence had a clear impact on deer, coyotes, and bobcats – and therefore, on the ecology of Jasper Ridge, underscoring the role both of apex predators and small preserves. In the U.S., 82% of protected areas are under 5 square kilometers (about 2 square miles), so they will likely be critical spaces for wildlife and plants as rapid urbanization continues, said Rodolfo Dirzo, study co-author and Stanford professor of biology in H&S.

“Maintaining sites where there is an entire community of animals, from predators to prey to the prey’s resource base, is very important,” he said. “When one piece is missing – and it’s typically the top predators that require larger areas and are more sensitive to human impact – we will no longer have fully functioning ecosystems.”

Mystery of mountain lion motivations
Why the mountain lions started to frequent Jasper Ridge is unknown. One theory is that the female mountain lions found the preserve to be a safe place to raise their young, as a mom with kittens has been spotted on camera during the study. Whatever the reason, they are only visitors. Mountain lions have a huge range in the Santa Cruz Mountains from 20 to 170 square kilometers (about 8 to 66 square miles). Jasper Ridge is far too small to have its own puma population.

Despite the occasional high-profile sighting of a mountain lion in San Francisco or in the suburbs, they tend to stay far away from humans, said Elizabeth Hadly, the study’s senior author and Stanford professor emerita of biology in H&S. They are also nocturnal, so they are not often on the landscape when people are active.

“Pumas are afraid of our smell and our sounds; they don’t like to see us moving,” said Hadly, who is also the former faculty director at Jasper Ridge. “Pumas use all of their senses to avoid humans.”

Humans are the No. 1 cause of mountain lion deaths, either through hunting or car accidents, Hadly pointed out.

“Clearly, we exert our own ecology of fear,” she said. “Humans are the ultimate predator on almost every landscape.”

Florida panther vs wild hogs

 In March 1987, Florida biologists released twelve radio-collared wild hogs into the Everglades to see if they could feed endangered Florida panthers by giving them something easy to kill. Bears ate two. An alligator ate one. Hunters poached three. A panther finally killed one after 117 days. By then, most of the hogs were already dead from everything except the animal they were supposed to feed.

The experiment came from a real problem. Florida panthers living south of Alligator Alley in the Fakahatchee Strand and the southern Big Cypress were in worse physical condition than panthers to the north. Food habits studies by the Florida Game and Fresh Water Fish Commission showed why. Panthers north of the highway ate mostly white-tailed deer and wild hogs, large prey with high caloric return. Panthers south of the highway were living on raccoons and armadillos, smaller animals that provide less energy per kill. The southern panthers were nutritionally stressed in the commission's language. In plain language, they were not getting enough to eat.

The idea was to test whether releasing hogs directly into occupied panther home ranges could supplement the prey base. The commission selected twelve castrated, pseudorabies-free wild hogs, fitted them with radio collars equipped with mortality signals, and split them into two groups.

On March 27, six hogs were released into the Fakahatchee Strand State Preserve within one kilometer of a radio-collared adult female panther. On March 28, six more were released in the privately owned Golden Gate area south of Alligator Alley within 200 meters of a different radio-collared female panther and her eight-month-old male kitten. The researchers monitored the hog collars every other day from the air, flying the same telemetry routes they used to track panthers. When a collar transmitted a mortality signal, a ground crew went in the same day to examine the carcass.

The swamp ate the experiment.

Two hogs were killed by black bears. One was killed by an American alligator. One was found eviscerated and partly covered with debris, which is consistent with a panther kill but could also have been a bobcat or another bear. Three hogs were killed by hunters, identified by knife marks on the radio collars. Two collars failed entirely and the hogs were never recovered. Two more collars were found on hog carcasses with no sign indicating what killed them.

One panther killed one hog. It happened 117 days after the release, nearly four months into the experiment, and was preceded by the deaths of at least eight of the other eleven hogs. The kill was made by a radio-collared adult male panther, not by either of the two females the hogs had been released next to. The females had home ranges of 160 to 350 square kilometers. The hogs stayed within four kilometers of their release sites.

The math was simple and unfavorable. The panthers they were meant to feed moved across enormous ranges while the hogs sat in one small area. The chances of a specific panther encountering a specific hog on a given night were low despite the radio locations showing both species in close proximity.

David Maehr and his co-authors at the commission published the results in the Florida Field Naturalist and concluded that the low number of released hogs made definitive conclusions impossible, but that the one confirmed panther kill suggested very large-scale releases might increase the prey base.

They also noted the obvious problem. The biological consequences and economic costs of large releases of hogs makes this a debatable management alternative. Releasing hundreds or thousands of hogs into the Everglades to feed panthers would simultaneously create an invasive species problem in a national preserve that was already struggling with feral hog damage to native vegetation and hydrology.

The experiment was never repeated at scale. The panthers south of Alligator Alley continued eating raccoons and armadillos. The genetic rescue that eventually saved the Florida panther population came not from supplementing the prey base but from supplementing the gene pool, when eight Texas cougars were brought in eight years later. We covered that story on this page with TX-101.

Twelve hogs were released to feed panthers. Bears, alligators, hunters, bobcats, and unknown causes killed eleven of them. One panther ate one hog four months later. The swamp took everything first because the swamp does not care about experimental design, and every predator south of Alligator Alley was hungry, not just the one the experiment was trying to feed.

Source: Maehr, D.S. et al. (1989). "Fates of Wild Hogs Released into Occupied Florida Panther Home Ranges." Florida Field Naturalist 17(2):42-43.

Fishers vs Canada lynx

Between 1999 and 2011, researchers in northern Maine radio-collared eighty-five Canada lynx and documented sixty-five deaths. Predation was the leading cause. Fourteen of those kills were attributed to fishers. You read that right, an animal that can weigh as little as eight pounds killing a cat that can weigh over twenty-five, the same cat that we recently wrote about killing mountain goats. It was the first time fisher predation on lynx had ever been documented anywhere in the world. It was not a fluke. It was a pattern.

The study was led by Scott McLellan, assistant regional wildlife biologist with the Maine Department of Inland Fisheries and Wildlife, and published in the Journal of Wildlife Management in 2018. The research began as a status assessment of Maine's lynx population, a federally threatened species whose numbers in the Lower 48 were not well understood. Nobody expected the primary finding to be that the leading predator of the lynx was a mustelid most people could not pick out of a lineup.

A fisher is not a small animal. A large male can weigh thirteen pounds and stretch over three feet from nose to tail. It is the second largest weasel in North America after the wolverine. But a Canada lynx weighs eighteen to thirty pounds, stands taller, has longer legs, and is built to run down snowshoe hares through powder snow. The size gap is real. The lynx should dominate every encounter.

In the forests of northern Maine, the opposite happened fourteen times in twelve years.

The researchers never witnessed an attack. They reconstructed them from the evidence. When a radio collar sent a mortality signal, the team tracked it to the location and worked the scene the way a forensic investigator works a homicide. They searched for the body, examined the neck and skull for bite marks, measured the intercanine width of the punctures to identify the predator, and read the tracks in the snow to determine what had happened before the kill.

The snow told the story every time. Fisher tracks connected with lynx tracks. The fisher had picked up the cat's trail and followed it. In multiple cases, the tracks led directly to a lynx bed where the cat had been lying down, resting or waiting out a snow squall. The fisher attacked the neck and held on.

McLellan told National Geographic: they just buckle on. Drag marks led away from the kill site to a cache location where the fisher had stored the body for later feeding. In one case, a fisher was found inside a tree cavity with lynx remains. In another, a radio-collared female and her uncollared kitten were both found cached at the same site. The fisher had killed the mother and the kitten.

In some attacks, the trauma to the neck was so extensive that researchers could not obtain accurate intercanine measurements because of the amount of repeated biting. The fisher had not delivered a single killing bite and walked away. It had stayed on the throat and kept working until there was nothing left to work on.

McLellan called the species a ball of fury. He said a fisher has no boundaries in the size of animal it is willing to attack. He was not overstating it.

The lynx is not the only predator the fisher kills. There are records of fishers killing fox, mink, otters, and raccoons in direct confrontation. Where fisher populations are dense, marten populations collapse because fishers hunt and kill them in the trees and on the ground. Bobcats, which fall in a similar weight range as lynx, are equally vulnerable.

The fisher is not always ambushing out of desperation. It presses confrontations against larger animals and wins the nerve contest because nothing in the weasel family has ever understood the concept of backing down.

McLellan told National Geographic he was unsure whether fishers take on coyotes but said it was possible. If a fisher can get a hold of the neck of an animal, he said, they are willing to hold on.

The hare cycle is the trigger that puts the fisher and the lynx in the same room. Canada lynx are snowshoe hare specialists. When hares are abundant, lynx are well-fed, strong, and operating in deep-snow habitat where fishers are less effective. When the hare population crashes, lynx weaken. Their bone marrow shifts from white and waxy to red and gelatinous, a diagnostic marker of malnutrition. A 2026 study published in Scientific Reports confirmed that when hare populations drop, habitat overlap between lynx and fishers increases. Both species contract into the same remaining cover.

Several of the lynx killed by fishers in the Maine study showed poor body condition at necropsy. A malnourished lynx bedded down in a snow squall is not the same animal as a healthy lynx running hares through powder. The fisher reads the difference in the tracks before it ever reaches the bed.

Fishers are not invulnerable though. Coyotes kill them. Black bears kill them. Great horned owls take juveniles. Wolves have killed fishers caught in the open on frozen lakes. The fisher exists in the middle of the food web, not at the top. But nothing else in the northeastern forest specifically tracks, ambushes, and kills an animal twice its size with the consistency that the fisher brings to lynx.

Not even the wolverine targets a specific larger predator with this kind of consistency. The wolverine is bigger, stronger, and operates on a larger stage, but it does not track lynx to their beds and kill them in their sleep as a matter of routine. The fisher does. If you put a fisher’s aggression and killing style inside a body the size of a wolverine, even wolves might end up on the menu. Luckily, that animal exists only in imagination.

That fourteen lynx in northern Maine were not dealing with imagination.

Source: McLellan et al. (2018), Journal of Wildlife Management. Maine Department of Inland Fisheries and Wildlife. National Geographic, January 2022. Scientific Reports, February 2026. National Trappers Association.