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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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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The Importance of Fieldwork and Field Skills

Young male mountain lion with a mule deer fawn killed by his mother.

Among my favorite activities is investigating mountain lion kill sites—meaning the work of actually going into the field and finding the remains of prey killed by mountain lions. We just published new research in the Journal of Mammalogy that shows that these expeditions in search of prey remains are not just enjoyable, they are also the best way to study carnivore foraging behaviors.

Every kill site is different, and some are tough to find. But over the years, I’ve begun to better predict where a cat might feel secure enough to feed and hide the remains of their prey. Flies are a great clue too—the sound and sight of them have often drawn me to a hidden carcass or a subtle area blood-flecked and sprinkled with tiny bits of tissue and bone easily overlooked. Magpies and eagles are even better, their vocalizations provide guidance from afar and if you can spot them on the ground, then you’ve found your kill.

Modern research on mountain lions relies heavily upon GPS technology built into collars. Location data are transferred via satellites to our computers while the collar is still on the cat, thus we can follow them in near real time. It’s absolutely amazing. When we see a group of location points on a map, we know a mountain lion has remained in place for some duration—what that animal was doing can only be determined with certainty by visiting the site to see what happened (and even then its not certain because we rely upon tracking skills to interpret signs; tracking will always be an imperfect art and science).

An elk killed and cached by a female mountain lion in northwest Wyoming.

Now it might be apparent to those who know me—that studying mountain lion kill sites brings together my dual interests in wildlife tracking and mountain lions. Its as if this work were created with me in mind. For the most part, our research teams (including those with professional tracking skills: Casey McFarland, Neal Wight, Matt Nelson, Max Allen, Michelle Peziol, Connor O’Malley, Anna Kusler, Blake Lowrey, and myself) spend almost all of our time visiting these sites in the field—its time consuming work, but I believe, well worth the effort.

Other researchers, however, invest elsewhere, and rely upon statistics and mathematics to measure kill rates (how often a carnivore kills prey) and even prey selection (what carnivores eat). They do this by visiting just a sample of locations in the field and then extrapolating what they observed to every area a mountain lion or other carnivore stopped and spent time, with the help of complex mathematical models. This approach is appealing because it saves lots of time in the field, and therefore money. Thus, the mathematical method has spread rapidly across the globe where it is being applied to more and more carnivore species.

My coauthors, Blake Lowrey and Heiko Wittmer, and I tested this mathematical approach to estimating kill rates against our own heavy-fieldwork approach, in which we try to visit every location a mountain lion stops for 4 or more hours on the landscape (we used to do 2 or more hours but 2-hr sites yielded very little prey data). We did this for 3 different study systems in which we’ve worked (Chilean Patagonia, Northern California, western Colorado), and found that the mathematical approach yielded unpredictably, inaccurate and imprecise estimates of kill rates. This was mostly due to the fact that carnivores are inconsistent in how they feed. They eat prey of different sizes, so the associated time it takes to consume their kills is highly variable. Mountain lions and other carnivores also have their kills stolen by bears and condors, and thus they sometimes feed for very short time periods from a large animal they killed. This confuses computer models, which tend to predict that places where a mountain lion spent little time must have been a place where it rested rather than killed prey.

An adult female mountain lion stands over an 11-month old elk calf she killed and cached.

Fieldwork is not just enjoyable, its justifiable. Spending time in the field remains our best approach to studying carnivore diets and kill rates. This is excellent news for those of us that have invested so much time in learning tracking skills, and so delight in forays afield where we apply our trade.