A new study shows that interactions between wolves and cougars in Yellowstone National Park are driven by wolves stealing prey killed by cougars and that shifts in cougar diets to smaller prey help them avoid wolf encounters.
The study, published at a time of growing overlap between cougar and wolf habitats in the western United States, found wolves occasionally killed cougars, but cougars did not kill wolves.
Researchers also found that cougars tend to avoid areas where wolves have made kills and stay close to escape terrain, such as climbable trees. Cougars responded to a decline in elk in the park by killing more deer, which they consume faster, leading to fewer interactions with wolves.
Published this week in PNAS, the study draws on nine years of GPS data from collared wolves and cougars and field investigations of nearly 4,000 potential wolf or cougar kills in Yellowstone. The findings suggest that coexistence between wolves and cougars depends less on overall prey abundance and more on prey diversity and the availability of escape terrain.
"In North America and worldwide, carnivore communities are undergoing major changes," said Wesley Binder, a doctoral student at Oregon State University and lead author of the study. "Our research provides insight into how two apex predators compete, which informs recovery efforts."
For much of the 20th century, government policies in the United States nearly eradicated both wolves and cougars. Cougar populations began to rebound in the 1960s and 1970s in the U.S. under protection. Wolf reintroduction started in 1995, including in Yellowstone. Both species are now recolonizing much of the western U.S.
"You've had these places that in the last 20, 30 years have had cougars come back, and now wolves are coming back as well," Binder said. "There are a lot of people asking questions like, 'What are our ecological communities going to look like now that we have both of these large carnivores back on the landscape?'"
Binder began his doctorate at Oregon State in 2022 after nearly a decade working on cougar monitoring in Yellowstone as part of the Yellowstone Cougar Project. His work included setting up a system of 140 remote cameras in the northern part of the park and catching and collaring cats.
The new study builds on decades of research showing that wolves dominate interactions because they live in packs, while cougars are solitary. Previous studies have demonstrated how subordinate carnivores exhibit a tradeoff with dominant carnivores; they suffer mortalities but also benefit from scavenging their kills. Yet cougars seldom scavenge other carnivore kills and are instead efficient hunters themselves, leading to unclear principles that govern their interactions with wolves.
Findings from the new paper provide some answers:
- Researchers investigated 3,929 potential wolf and cougar kill sites: 852 were wolf feeding events, and 520 were cougar feeding events.
- Wolves made 716 kills and scavenged 136 times, primarily on elk (542), bison (201) and deer (90).
- Cougars made 513 kills and scavenged seven times, mainly on elk (272) and deer (220).
- Comparing data from 1998-2005 and 2016-2024 revealed major shifts:
- For wolves, bison increased from 1% to 10%, and elk declined from 95% to 63%.
- For cougars, elk dropped from 80% to 52%, and deer increased from 15% to 42%.
These kill site investigations were then used to train machine learning models that used GPS data to predict wolf and cougar kill sites. This allowed researchers to pair all wolf and cougar movements with probable kill sites and identify the drivers of their interactions. They found wolf-cougar interactions were highly asymmetric: 42% occurred at predicted sites where cougars killed prey, and only one happened at a site where a wolf killed prey.
The researchers documented 12 adult cougar deaths from 2016-24, two of which were caused by wolves. In both events, no escape terrain was available, and the wolves didn't consume the cougars but ate the elk the cats had killed. They recorded 90 wolf deaths during the same period, none of which were attributed to cougars. Most were due to natural causes or human actions.
Co-authors of the paper are Joel S. Ruprecht, Rebecca Hutchinson and Taal Levi of Oregon State's College of Agricultural Sciences; Jack Rabe of the University of Minnesota and Yellowstone Center for Resources; and Matthew Metz and Daniel Stahler of Yellowstone Center for Resources. Hutchinson is also part of Oregon State's College of Engineering.
