A look at the delicate balance between wolves, mountain lions, coyotes, and the ungulates they hunt.

It was early June, and I had just come into Lamar Valley to see every wildlife watcher’s dream: the Junction Butte pack hunting bison on the valley floor. We pulled over the car, set up the scopes and spent the next two and a half hours watching the back-and-forth battle of wolves pushing bison herds and chasing the young, and then the bison mounting a counter charge and causing the wolves to retreat to a safe distance. After many nearly successful attempts by the Junctions, and a well-placed kick from a female bison, the pack moved off to bed down through the heat of the day. Perhaps they would try again later, but this attempt had been thwarted.

Although the chances of witnessing a predation event are relatively low, the details of predator-prey relationships in the park are a focus of the Yellowstone Wolf Project, Cougar Project, elk research and the Elk Calf Study. This team of scientists monitors Yellowstone’s predators and their effect on prey. In 2024, the team spent 4.5 months across the year studying predation. They were able to identify over 260 different kills, 211 of them from wolves, and 56 of them from cougars. While these 267 kills likely don’t cover every single predatory event throughout the year, they act as a very good representation for what Yellowstone’s wolf and cougar diets looked like. Of the carcasses sampled, 82% of all wolf kills were made up of elk and bison and 67.9% of all cougar kills were made up of elk or deer. These studies have also revealed that predators are disproportionately targeting younger prey, as well as female prey.

While those statistics are interesting, consider the implications for what they mean in the context of the ecosystem. Within wildlife biology, there is a concept known as carrying capacity. This concept states that there is a certain number of animals within a species that an ecosystem can support. Here in the park, the current population of wolves is around 100 adult animals, and it’s been fluctuating around that threshold since 2008. This 100-animal population size, or carrying capacity, is influenced by a number of factors, including disease transmission, competition with other wolves, and food availability. For cougars, current estimates put the population somewhere between 34 and 42 individuals, with carrying capacity likely near that range.

If we look at the population graph for wolves over the last 30 years, a very clear early spike can be seen in the early 2000s. This “overshoot” of the carrying capacity is common when a predator is reintroduced to a landscape. Oftentimes, in the absence of predators, and with wildlife management norms of the twentieth century, it was common for prey species, like elk, to overpopulate landscapes, and have few ecological controls. This was the situation in the northern range of Yellowstone in the 1990s when the northern elk herd numbered upwards of 17,000 individuals. With an abundance of food on the landscape due to this overpopulation, wolves were able to quickly reproduce and expand their population to over 170. However, by the late 2000s, elk populations started to return to a more sustainable level, not only because of predators returning to the landscape, but also because of a variety of management actions and circumstances. These included a recovery of bear and cougar populations, late season cow elk hunts outside of the park, a prolonged drought and series of severe winters, and competition with increasing bison herds. As elk populations fell, other ecological stressors, such as increased competition with other predators caused wolf populations to slowly decline and level out to the stable and healthy population we see today.

A beautiful thing about carrying capacities is that in a healthy ecosystem, carrying capacities exist such that predator and prey populations become very closely tied together. In years of abundant plant growth, elk calf survival might be higher than normal, and therefore the prey population could increase. This could cause a connected response of predators with more available food in following years leading to higher wolf and cougar survival and perhaps their population increasing. As the prey population begins to fall once more, the predator population will follow. In a healthy ecosystem, these populations exist in a harmonic balance, oscillating above and below the carrying capacity for their species. The predation and population dynamics of wolves and cougars of Yellowstone teach us that beneath every action, every situation, and every population we find in the park, there is a complex web of relationships, interactions, and interdependence.

It’s this complexity that I find brings me back to wildlife watching. Being out there, watching wolves hunt is an experience unlike anything else I have experienced. The range of emotions that are felt when, for example, you watch a wolf pack sneak off with a newly born bison calf can be overwhelming. The pure excitement for the pack, and honestly some underlying sadness for the life the calf didn’t get to live. But, at least for me, understanding what predation means for the landscape, and health of a wild ecosystem, like Yellowstone, acts as a certain type of centering force. It allows me to refocus on the now, and it’s what keeps me waking up at 3:30am to get out there for the chance to see it all again.

by Kyle Wonders, Yellowstone Forever Institute Lead Field Educator

 

Feature Photo: Lead Field Educator, YF / Amanda Evans