Plague in Yellowstone Mountain Lions

An adult male mountain lion.

Plague is a highly-contagious, deadly disease caused by the bacterium Yersinia pestis. The Black Death, for example, killed some 75-200 million people from 1346-1353, after which it took 200 years for the world’s human population to recover. But plague is not just a horror of history. It is still very much alive today, living in the soils where we live, work and play. For the most part, we remain unaware of its presence unless a colony of prairie dogs or ground squirrels dies and their carcasses draw our attention. In a new paper just published in Environmental Conservation, we report startling results of plague testing in mountain lions from our Teton Cougar Project. We sampled over a nine year period, overlapping a case in which a boy scout contracted plague in our study area.

We detected plague exposure in 43% of 28 mountain lions tested for plague. Over the same time period, 4 mountain lions died of plague. Other researchers have been documenting high levels of plague exposure among mountain lions as well—along the western slope of the Rockies in Colorado, and in southern California, for example. Some have even speculated that mountain lions could carry the bacterium long distances if a young animal seeking a territory were infected.

We concluded that Y. pestis may be present at higher levels in the Greater Yellowstone Ecosystem than previously thought, and that plague is a concern for local mountain lions. We also believe mountain lions may be a useful sentinel to alert people about the potential risk of plague in areas across the West, because of their current status as a hunted game species. More than 3,000 mountain lions are killed by hunters each year and presented to state and provincial wildlife agency personnel. State personnel could sample these animals, which in combination with the locations of where they were killed, could be used to refine maps of potential exposure to humans. Please note, that we are not arguing for increased mountain lion hunting, or that plague testing is sufficient reason to hunt mountain lions. We are only pointing out that where they are hunted, they could provide useful data to improve human safety.

Last, we would emphasize that the average person has essentially zero possibility of contracting plague from a mountain lion. So please, do not read into our results as a reason to fear mountain lions. The vast majority of people in the USA will never be lucky enough to see a wild mountain lion, let alone be close enough to interact with their body fluids. Nevertheless, hunters and others handling mountain lions in the Yellowstone region should be aware of the possibility of exposure. Knowledge is power. In 2007, my friend and mentor, Eric York died from plague he contracted from a mountain lion in Grand Canyon National Park. His terrible death reverberated through the research community, causing shock and mourning. And it could have been avoided if people had considered the possibility that he had plague and administered appropriate antibiotics. Eric was one of the best field biologists I’ve ever met. He drank from a coffee mug each morning labeled “FTP,” short for “For The Puma.” Everything he did, dawn to dusk, was for mountain lions.

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Mountain Lions as Ecosystem Engineers

Adult female mountain lion, Olympic Peninsula. Photograph by Mark Elbroch

The keystone rock is an arch’s linchpin providing structural strength and integrity—remove it, and the structure topples and falls. Ecosystems function in much the same way. Keystone species are animals that disproportionately influence their environment, and often those that best support ecosystem health and biodiversity. An ecosystem engineer is one type of keystone species—they are animals that create or modify habitat for other animals, generally increasing biodiversity in local areas and the amount of types of habitat available for wildlife.

Think of American beavers. Beavers dam streams, which changes water speed, water depth, and subsequently, water temperature. Deep, still beaver ponds that sit and soak up sunlight support different fish, plant, and bird life than the fast-running portions of the same stream. Without beavers, the stream as a whole would support less kinds of flora and fauna, which we collectively call biodiversity.

In research recently published in the prestigious journal, Oecologia, we show that mountain lions are ecosystem engineers that create essential habitat for carrion-dependent beetles. It is the first research to show that an apex predator plays the role of engineer. In collaboration with graduate researcher, Josh Barry, and Dr. Melissa Grigione at Pace University, we collected and identified 24, 209 beetles across 18 sites, representing 215 unique beetle species. The carcasses abandoned by mountain lions were not just food for beetles, but the very places beetles spent their lives, hiding from predators, seeking mates, raising young, and morphing from larvae into adult forms that dispersed in search of the next carcass to begin the cycle all over again.

Photograph by Josh Barry / Pace University and Pace University

Ecosystem engineers and other keystone species are those animals that are the critical puzzle pieces that connect to the most other pieces, they are the species that disproportionately hold ecosystems together, and they are the species that require conservation attention to ensure their populations are healthy. Mountain lions are one such species. Mountain lions create more large carcasses than other predators (for example, wolves tend to dismantle prey into many small chunks), which recent research has shown is more important to ecosystem health. They feed more mammals and birds than any other predator, increasing the number of animal interactions (e.g. links in food webs) so essential to maintaining ecosystem resilience. And they are ecosystem engineers on top of this as well.

Mountain lion predation, we’re learning contributes to local biodversity and ecosystem health and more. Photograph by Mark Elbroch

We are only just beginning to unravel the positive roles that mountain lions play in supporting healthy natural systems, and they are already startling. Evidence suggests that maintaining healthy mountain lion populations across the Americas is an important step to maintaining healthy ecosystems that sustain complex biodiversity, including human beings. Put another way, when we aid mountain lions we ultimately help ourselves.

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The Olympic Cougar Project


M16, a male puma being followed as part of the new Olympic Cougar Project. Photograph by Mark Elbroch

Panthera’s Puma Program has been silent for awhile, but we’ve not been idle. We’ve been changing and growing, and we’re launching new projects in both North and South America. Here, we introduce the Olympic Cougar Project. It is a large-scale, multi-national collaborative effort, in which we’re assessing mountain lion (or cougars as they are locally called in the Pacific northwest) connectivity in western Washington State.

Previous research on the genetic diversity of mountain lions in Washington State highlighted that cats on the Olympic Peninsula west and south of Seattle may already be in trouble. They are genetically less diverse than those on the mainland, likely because the Peninsula’s mountain lions are isolated from mainland populations. Without doubt, the situation is getting worse.

The Olympic Peninsula is fast becoming an island. The Interstate-5 (I-5) highway corridor south of Seattle is one of the fastest developing regions on the west coast, and is increasingly severing wildlife connectivity in western Washington.

Location of the Olympic Cougar Project. The red arrow denotes connectivity between the Peninsula and the mainland across the I-5 corridor. 1=Makah Tribe, 2=Lower Elwha Klallam Tribe, 3=Jamestown S’Klallam Tribe, 4=Quinault Tribe, 5=Skokomish Tribe

South of the peninsula lies the massive Columbia River, forming a considerable barrier for mountain lions traveling that direction. Discharging more water than any other river in the northwest, a mountain lion would need to swim about 6 miles to cross the mouth of the river. Mountain lions that wind their way eastward, closer to I-5, can shrink that crossing to a feasible swim as short as 2/3 of a mile. There are stories of mountain lions swimming across water bodies up to a mile wide, but much of the river south of the Olympic Peninsula is 2-6 miles wide.

West of the peninsula lies the Pacific Ocean, and to the north the Strait of Juan de Fuca which, at its narrowest point, offers a 15-mile swim to Vancouver Island across shipping lanes full of massive ships and hungry orcas. The bustling Puget Sound sits to the east. Navy shipyards, ferry traffic between Seattle and offshore islands, and poisonous trace metals from old industry seeping into the estuary make this area treacherous for any wildlife, pumas included.

Looking at all the options, the south and the east are still the best possibilities for pumas to immigrate and emigrate from the Peninsula. However, this means traveling through increasingly developed areas along the I-5 corridor from Tacoma, WA southward to the Oregon border. Certainly to the south, closer to Oregon, that path is much less developed and much easier, but with time the highway will widen and infrastructure and communities will grow to create a wider developed corridor, and a noose for wildlife like mountain lions, that require large connected landscapes to maintain their health over time.

F6, an adult female mountain lion (or cougar) being followed by our new Olympic Cougar project. Photograph by Mark Elbroch

Ultimately, our goal is to map mountain lion connectivity, identify bottlenecks and blockages in wildlife corridors, and work with state developers to ensure I-5 is modified to aid wildlife on the Olympic Peninsula for generations to come. Within this umbrella, we’re also studying mountain lion dispersal, assessing competition between mountain lions and bobcats, and working with an incredible array of talented scientists to analyze movement and genetic data collected from mountain lions throughout western Washington.

Our core team is composed of people working for the Lower Elwha Klallam Tribe (LEKT), and Panthera scientists. LEKT received funds from the Administration for Native Americans to study mountain lions and predation as part of building their Seventh Generation Wildlife Management Plan, to guide the Tribe in the sustainable use of natural resources. Kim Sager-Fradkin, Wildlife Program Manager, leads the LEKT team, and I lead the Panthera team. Cameron Macias is the first LEKT tribal member to attend graduate school to study natural resource management, and is analyzing mountain lion and bobcat genetic samples collected in our study, with support from a Panthera Kaplan Graduate Grant. Together, LEKT and Panthera are forging alliances with additional tribal partners and the Washington Department of Fish and Wildlife Department to share existing data sets and strategically gather additional data to fill knowledge gaps on the Peninsula’s wild cats.

An intimate video of M16 as he investigates his first encounter with one of our motion-triggered video cameras.

With the Olympic Cougar Project, we’re attempting something bold, something big, and something swift to protect key routes that will maintain and increase connectivity among pumas in western Washington. In the face of industrial development, urban sprawl and natural hazards, it’s a colossal undertaking, but the results will be rewarding beyond belief. If we succeed, and we will, our work may save untold thousands of cats and other animals long into the future. Join us to support the effort. And stay tuned, there is so much more to come from the Olympic Cougar Project.

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Common Sense Conservation to Keep Kittens Safer

Three of F61’s kittens in a typical fortress of downed wood, in which she gave birth. Photo by Mark Elbroch.

An early snow had painted the landscape completely white, and we were navigating the slippery roads of backcountry northwest Wyoming as part of Panthera’s Teton Cougar Project. We paused to look at footprints of a mountain lion we called F61, where she crossed the road and climbed towards the ridgeline. Just up the road, we found a houndsman’s truck tucked up against the trees. I turned off the engine and we stepped out into the crisp, still air. We did not hear the baying of hunting hounds—perhaps he hadn’t found her. Just ravens and wind.

We knew that F61 was nursing four tiny kittens at the time, tucked up in a woody fortress to the south across the river. If she were killed, four more mountain lions would die. It’s an unavoidable reality that, on occasion, hunters unintentionally kill females with dependent young—subsequently dooming the kittens along with their mother.

This is why we conducted new research just published in the Wildlife Society Bulletin. We set out to study female movements and behaviors while they were caring for the youngest and most vulnerable kittens in the den (See this blog for a description of a puma den). “Denning” is the period beginning when kittens are born and ending when they start traveling with their mother to her kill sites.

F61 with her 4 tiny kittens in the den. Photo by Mark Elbroch

We used 12 dens to determine the average length of denning, and 34 dens we documented over the course of our work to determine the following—if we delay legal mountain lion hunting until December 1 each year, we can avoid the denning period for 91% of mountain lion families.

Such a change would allow hunters the best opportunity to detect mountain lion family groups in the field, and to avoid inadvertently hunting females with kittens. It’s also a change that provides mountain lion families greater safety while their kittens are most vulnerable. It’s also a change that reflects a growing appreciation for predators in an evolving world.

In my mind, it’s just common sense conservation.

The morning after our encounter, Michelle Peziol, the Project Manager of Panthera’s Teton Cougar Project, followed F61’s trail from where we’d found her tracks crossing the road. Climbing the hill and traversing the ridge line, she saw that the mountain lion’s trail was intercepted by a hunter on horseback and his hounds. She discovered the tree where F61 had sought refuge. The area was a mess—churned up by the feet of cat, baying hounds, horse, and man.

A portrait of F51 and her kitten. Photo by Mark Elbroch

At the same time, I toured F61’s usual haunts and found her using the beacon in her collar. The hunter had let her go. I caught up with him several days later. He was gracious and recounted a beautiful day on the mountain—his first day hunting of the year, he said. He described F61 well, saying he’d noticed her collar and realized she must be one of the mountain lions we studied. He valued research, so he hauled in his hounds and walked away, letting her be.

The hunter had spared F61, and in doing so, had saved the lives of four more mountain lions, too. He was more than relieved when I told him.

This is simple change that can aid mountain lions right now. Spread the word: Delay mountain lion hunting seasons in western states until December 1 to protect the youngest kittens. It’s common sense conservation that we can apply immediately to increase protections for mountain lion families in hunted populations, supporting the shared goals of conservation scientists, wildlife advocates, and hunters alike.

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A Perfect Storm: How Multi-Jurisdictional Management Affects Mountain Lions

A subadult mountain lion, an age group our research has shown is particularly vulnerable to current management strategies. Photo by Mark Elbroch


Among the hallmarks of the American West is its mosaic of public lands, each governed by one of several state and federal agencies with different missions and objectives and, thus, varying impacts on the wildlife that call them home.

Our newest research, just published in the scientific journal Ecology and Evolution, reveals what happened to mountain lions that crossed jurisdictional boundaries and felt the effects of multiple management strategies simultaneously. We found that a perfect storm of three overlapping management actions dating back to the mid-1990s have contributed, sometimes unintentionally, to the 48-percent decline in the mountain lion population north of Jackson, Wyoming.

It all started in 1995 and 1996, when wolves absent since 1926 were re-introduced to Yellowstone National Park as part of efforts to restore natural and cultural resources to lands overseen by the National Park Service. Without a doubt, this is one of the most successful conservation stories of all time, both in terms of its cascading ecological benefits for a complex ecosystem and the social benefits it brought to our people.

In about 2000, managers turned their attention to the Jackson elk herd, the primary food source for the mountain lions we studied. A collaboration between state and federal agencies set forth objectives to reduce the herd from about 16,000 to 11,000 animals through “liberal” hunting measures. This objective, too, has been achieved in recent years.

Elk migrating northward out of the National Elk Refuge across Grand Teton National Park.


Finally, in 2007, the Game Commission for Wyoming Game and Fish Department encouraged increased mountain lion hunting on public and private lands across the state to reduce mountain lion numbers and their associated risks (both perceived and real) to people and livestock. This objective, too, has been achieved. The results of these three different management actions have brewed unexpected outcomes, and been hard on mountain lions.

M68, a subadult male mountain lion in the background, chased off his kill by the wolf in the foreground in northwest Wyoming.


Our research focused on mountain lion mortality rates, using 14 years of monitoring data from 134 individually marked mountain lions. Wolves impact local mountain lions in multiple ways, but one of them is by killing kittens. Even while people were increasingly killing adult and juvenile mountain lions across the state to meet State objectives, wolves had begun killing mountain lion kittens after being restored to the area. Wolves were responsible for the death of at least 18% of the kittens we followed (we were not always able to determine the cause of death).

Simultaneously, wolves were influencing where elk congregate on the landscape, and how many were available for mountain lions to hunt. The distribution of elk, in fact, has become vexingly skewed, and contrary to efforts by managers to encourage a broader distribution, a greater proportion of the remaining herd winters on the National Elk Refuge each year. Local biologists attribute this change to wolves and changing weather patterns.

Elk that congregated in the open on the Refuge were still prey for wolves, but not for mountain lions that could not compete with wolves away from the protection of trees and cliffs. As elk numbers dropped in our study area, following established management objectives to reduce the herd, they also changed their distribution. In combination, this has resulted in an amazing 70-percent reduction in the number of elk that winter on native range surrounding the National Elk Refuge, where they can be hunted by and sustain local mountain lions. Juvenile mountain lion survival plummeted, and we saw mountain lions of all ages increasingly die from starvation.

70 percent reduction is huge! And the remaining 30 percent of elk—around 2,500 individuals—must now be shared with the local wolf population, which over the course of the study increased by 600 percent and now outnumber mountain lions at least 3 to 1. Suddenly, it doesn’t seem so surprising that mountain lion numbers are down—adults and kittens are being killed, and their food resources are greatly reduced.

We’ve just completed the next step in our research, which is to make recommendations to aid the recovery of mountain lions. Unsurprisingly, we emphasize the need to redistribute elk on the landscape, a concept easy to propose but very difficult to implement on the ground in a system with multiple predators, multiple jurisdictions, and multiple management objectives all interacting with each other in sometimes unexpected ways.

We also recommend reducing mountain lion hunting in areas where wolves are rebounding—the cascading effects of their presence are apparently too much for the cats to handle when already under pressure from human hunters. Finally, this study shows the need for managing whole ecosystems in complex areas like the West where various stakeholders hold different objectives for wildlife, sometimes complimentary, sometimes contradictory. In this case, it is the mountain lion that suffered.

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Eastern Cougar “Extinction” — Some Key Points


The eastern cougar is not extinct, it never existed–here is a mountain lion from the west, which genetics confirm is as much an eastern cougar as those cats that historically roamed New England.

I’ve received a lot of worried messages and comments on social media about the recent U.S. Fish and Wildlife declaration that the “eastern cougar” (or mountain lion, Puma concolor couguar) is extinct, and was therefore being removed from federal endangered species protections. I think the wording of the federal ruling unintentionally—but unfortunately—influenced how the media covered the change in conservation status.

Here is the complete federal ruling, but here I provide what I believe are the five key take-home messages for those of us invested in mountain lion conservation. This is just one man’s opinion, of course.

  1. There never was an “eastern puma/cougar.”

This is one point I believe should have been included in the summary at the start of the federal ruling. Yes, the fact that there is not a breeding population of “eastern cougars” in the northeast of the United States or eastern-most Canada is reason for the declaration. But, much more importantly, the newest science has revealed that there never was an “eastern cougar” subspecies to begin with.

Phylogeny is the science that proposes how animals are related by their evolutionary history. Think of phylogentic trees, something most people can remember from school, and the “tree of life” showing how animals evolved and are related to each other. Today, phylogenetics is the more appropriate term, because our study of phylogeny is almost entirely dependent upon genetic tools.

In the old days, phylogeny was proposed based upon morphology (the shape, color, and external characteristics of an animal and its skeleton). Based upon subtle differences in coat color and skeletal measurements, historic scientists believed there were many subspecies of mountain lions in North America, including the eastern cougar. Genetic tools, however, have provided a very different picture.

The International Union for Conservation of Nature (IUCN) currently recognizes six subspecies of mountain lions, of which only one—Puma concolor cougar—inhabits North America. This means that current genetic research supports the belief that all the mountain lions in North America are of a single subspecies. In other words, the eastern cougar was never a separate subspecies, and mountain lions that historically inhabited the northeast of North America were the same subspecies as the mountain lions in Idaho—which are still very much alive. Thus, the eastern cougar is not extinct—it never existed.

It is more correct to say that the North American subspecies of mountain lions is locally extinct in the northeast, because there is not a breeding population in this region.

  1. Recent and future mountain lions in the northeast are not eastern mountain lions.

Any recent news of mountain lion sightings in the northeast, and any future confirmations of mountain lions in the northeast, do not justify the existence of the “eastern cougar” as a separate subspecies. These are migrants from the west, not local mountain lions that survived undetected for the last 70 years. Even if there was evidence that some of these new migrants were breeding, that is still not evidence of eastern mountain lions. These are the North American subspecies of mountain lions returning to where they were extirpated some 70 years ago when wide-scale predator control was commonplace.

Tracks of an adult female mountain lion from northwest Wyoming (F72). Photograph by Mark Elbroch

Some people still argue that mountain lions have existed in hidden pockets in New England for all of these years. Importantly, this does not matter because the subspecies distinction of “eastern cougar” was incorrect. But, further, most people agree this is unlikely. New England has numerous people skilled in interpreting animal tracks and sign, and mountain lions leave considerable sign where they move and kill prey.

Consider the amazing adventure of the dispersing male mountain lion that was killed on a Connecticut highway in 2011—and subsequently became national news and was written up in the book Heart of a Lion. Documenting this lone male was akin to looking for a needle in a haystack when you consider the massive geographic range he traversed, in which he unlikely ever encountered another mountain lion east of the Mississippi (if not east of Kansas). Yet, even he was documented numerous times on motion-triggered cameras and by experienced woodsmen and women while he traveled. Paul Rezendes and I were two of the many that confirmed photos of footprints he left in the Quabbin Resevoir in central Massachusetts before he was killed. My point is that even a single cat without a territory leaves sign, and a resident breeding population leaves much more.

  1. Eastern migrants are unaffected.

Mountain lions that disperse eastward from the west were never protected under the Endangered Species Act. Thus, current and future eastern migrants are unaffected by the new federal ruling—and still protected following the laws of the states in which they move while they are dispersing to seek new territories to call their own.

This map was made by Brad Herried for the Cougar Network, an organization leading the documenting and analyzing the eastward expansion of western mountain lions.

  1. Introducing mountain lions in the east just got easier (probably).

Re-introducing animals into previous range (as was done with wolves into Yellowstone National Park and central Idaho in 1995 and 1996) is an arduous process. Re-introducing federally protected animals, which are monitored closely and have stringent rules about how they are handled and moved, is even more difficult.

The U.S. Fish and Wildlife Service and numerous conservation scientists agree that delisting the eastern cougar actually makes it easier to reintroduce this top predator in the northeast. For one reason, now that all mountain lions in North America are considered the same species, we can reintroduce the native subspecies to New England rather than replace it with a different subspecies. It will now be up to each state to decide whether that is a course they would like to pursue, however, the debates between pro-predator and anti-predator constituents are unlikely to be any easier

If you live in an eastern state that is deliberating reintroduction, or if you would like then to consider it as an option, get involved, reach out and contribute your thoughts. State Wildlife Agencies act on behalf of their public—so let them know how you feel. Certainly, there are numerous areas that could sustain mountain lions in the northeast.

  1. The Florida panther is unaffected (at least for now).

The Florida panther, Puma concolor coryi, is listed separately from the eastern mountain lion, and its status under the Endangered Species Act is unaffected by the recent federal ruling. The 80-100 wild Florida panthers remain protected wherever they are found, even if they disperse out of Florida into neighboring states.

The caveat, however, is that current phylogentics could be used to argue that the Florida panther subspecies, just like the eastern cougar, is not justified either, and that their protective status should be ended as well. This would be devastating for Florida panther conservation, which is currently led by the U.S. Fish and Wildlife Service. This is something conservation scientists, advocates, and managers need to monitor closely as the status of Florida panther is reviewed by the U.S. Fish and Wildlife Service.