They lurk in the mountains, leading solitary, nearly unnoticed lives. But while grizzly bears and wolves hold Yellowstone National Park’s large carnivore spotlight, mountain lions quietly thrive as one of the ecosystem’s major predators.
Largely forgotten by the park-going public, cougars get plenty of attention from park wildlife biologist Daniel Stahler. Stahler just completed the fourth winter of a five-year study to better understand how the cougar population is responding to landscape and prey competition from growing grizzly bear and grey wolf populations.
“We’re viewing this as a multi-carnivore system, which makes Yellowstone unique and special,” Stahler said. “Yellowstone today is as carnivore rich as it has been in over 150 years. In terms of ecosystem restoration, it’s a wonderful success story.”
And while the study isn’t yet done, data shows the cougar population in the park is adaptable and thriving.
Mountain lions in the Rocky Mountain West shared a fate with other feared predators of the region. By the 1920s the last cougars in Yellowstone ecosystem were gone. Like wolves they had been poisoned, trapped and shot until extirpated, Stahler said. But while wolves required human help to return to the park, cougars crept back on their own, re-establishing a small but robust population of about 15 to 22 animals in the late 1970s and early 1980s.
Wildlife management helped the species rebound. Regulations treated mountain lions as trophy animals with hunting quotas and restrictions instead of as predators which could be indiscriminately killed on sight.
Park biologists launched the first of three major cougar research initiatives in the 1980s with the goal of establishing a baseline population estimate. Scientists again studied the animals from 1998 to 2006, this time looking at how wolf reintroduction and a growing grizzly bear population impacted the lions of the park.
“It was an era of carnivore restoration,” Stahler said. “Everything was coming back, but it meant they all had to share the landscape.”
Despite competition with the other carnivores, the estimated cougar population rose to more than 40 animals, Stahler said.
“It’s a wild place, there’s a lot of food and habitat and these carnivores could sort themselves out,” he said.
That second research project also explored new, non-invasive ways of studying the animals such as tracking them with DNA from hair left on rocks, branches and even in tracks, said Michael Sawaya, a wildlife ecologist who worked on the study. Researchers were able to learn about the population without actually handling and collaring animals.
In 2014, Stahler and other biologists wanted to again check on the cougar population and started the current five-year study to see how declining elk populations and increasing competing predator populations were impacting the mountain lions.
The new research gives a complete picture of how many predators are on the landscape and what that means for elk populations, Sawaya said. Yellowstone offers a unique place to study because the population is un-hunted and in a protected area. The data shows how the animals survive in a protected system, he said.
Stahler is focusing on cougars in the northern part of Yellowstone where the animals live year-round. He tracks the animals to bed sites where he collects hair samples they’ve left behind.
Stahler recently wrapped up field work and hasn’t analyzed this winter’s data, but based on findings from the previous two years, he believes there are 22 unique animals in the park.
“That’s a pretty healthy population,” he said.
The stable numbers show that even as elk decline, mountain lions can find other food and thrive despite sharing the landscape with more carnivores.
“Wolves have had a significant force on the landscape, but cougars have adjusted,” he said.
Stahler also collared three mountain lions to track their predation habits. The study gives a sense of how cougars use the landscape. The findings can be applied to other areas where humans are encroaching on mountain lion habitat.
“This is valuable data in looking at conservation of these carnivores,” he said.
The research project will continue for one more winter. Once complete, researchers plan to compare the fresh data with those of previous studies, including one set dating from the 1980s. Population monitoring is the primary aim, but scientists hope also to gain a better understanding of genetic diversity within the cougar population in the protected system.
Sawaya and his colleagues would then like to see an expanded version of the study done ecosystem wide across state and federal jurisdiction to give a bigger picture of how these types of carnivore populations, which need large swaths of land, survive.