A new study sheds light on the tense relationship between wolves and cougars in Yellowstone National Park. Researchers have found that many cougar encounters begin with wolves taking over prey that the cougar has already killed. To reduce these dangerous encounters, cougars can adapt by targeting smaller animals and avoid crossing paths with wolf packs.
The study was conducted as wolf and cougar territories increasingly overlap in the western United States. Wolves have sometimes been responsible for killing cougars, but scientists have found no evidence that cougars have killed wolves.
How cougars avoid encounters with wolves
The study also found that cougars stay away from areas where wolves have made recent kills. They tend to stay near shelters such as trees that they can quickly climb if threatened.
As elk numbers declined in Yellowstone, cougars shifted their focus to deer. Because deer are smaller and can be eaten more quickly, this change reduces the amount of time cougars spend near carcasses, making it less likely that wolves will show up.
9 years of GPS tracking and field surveys
Published this week: PNASThe study utilized nine years of GPS tracking data from collared wolves and cougars. Researchers also conducted field surveys at approximately 4,000 potential murder sites within the park.
The findings suggest that the ability of these two apex predators to coexist peacefully depends more on the diversity of prey species and access to safe havens than on the total amount of prey available.
“Carnivore communities are undergoing major changes, not just in North America but around the world,” said Wesley Binder, a doctoral student at Oregon State University and lead author of the study. “Our study provides insight into how the two apex predators compete, which can aid recovery efforts.”
The changing landscape of the American West
For much of the 20th century, federal and state policies nearly wiped out both wolves and cougars in the United States. Cougars began to recover under legal protection in the 1960s and 1970s. Wolves have been reintroduced since 1995, including in Yellowstone. Both predators are now expanding into areas of the western United States where they have long been absent.
“There were places over the last 20 to 30 years where cougars were coming back, and now wolves are coming back as well,” Binder said. “A lot of people are asking questions like, ‘What will happen to our ecological communities if both of these large carnivores come back here?'”
Binder began his doctoral work at Oregon State University in 2022 after spending nearly a decade observing cougars in Yellowstone through the Yellowstone Cougar Project. His efforts included installing 140 remote cameras in the northern region of the park to capture and outfit cougars with tracking collars.
Why do wolves have the upper hand?
Decades of research have shown that while wolves hunt in packs, cougars are solitary and typically have an advantage in such interactions. In many predator systems, smaller or less dominant carnivores face trade-offs. They risk being killed, but may benefit from preying on dominant predators. But because cougars rarely scavenge from other carnivores and are skilled solo hunters, scientists remain unclear about what actually shapes wolf-cougar interactions.
This new study provides a clearer answer.
- Scientists investigated 3,929 potential kill sites associated with wolves and cougars. Of these, 852 were wolf feeding events and 520 were cougar feeding events.
- Wolves made 716 kills and scavenged 136 times. Their primary prey included elk (542 animals), bison (201 animals), and deer (90 animals).
- Cougars killed 513 animals and only foraged seven times, focusing primarily on elk (272) and deer (220).
- Comparing data from 1998 to 2005 and 2016 to 2024 reveals the following major changes:
- For wolves, bison’s diet increased from 1% to 10%, while elk’s diet decreased from 95% to 63%.
- For cougars, elk decreased from 80% to 52%, while deer increased from 15% to 42%.
Machine learning reveals asymmetric conflict
The researchers used confirmed murder scene data to train a machine learning model that combined GPS movement patterns with likely murder scene locations. This approach allowed us to match predator movements with possible feeding events to better understand when and where wolves and cougars interact.
The results showed a significant imbalance. Approximately 42% of wolf-cougar interactions occurred in areas where a cougar would be expected to make a kill. Only one interaction occurred at the scene where the wolves killed their prey.
From 2016 to 2024, researchers recorded 12 adult cougar deaths, two of which were caused by wolves. In both cases there was no shelter nearby. The wolves did not eat the cougar, but instead ate the elk that the cougar had killed.
During the same period, 90 wolf deaths were recorded. None of them were caused by cougars. Most wolf deaths are related to natural causes or human activities.
Co-authors of the study include Joel S. Ruprecht, Rebecca Hutchinson and Tar Levy of Oregon State University of Agricultural Sciences. Jack Rabe of the University of Minnesota and Yellowstone Resource Center; Matthew Metz and Daniel Stahler of Yellowstone Resource Center. Hutchinson is also committed to Oregon State Tech.
