For decades, the cougar (Puma concolor) has been thought of as a loner predator, running across other members of its species only to mate or to fight.
But a new study now shows that, contrary to popular belief, cougars have quietly built for themselves a rich, hierarchical society based largely on sharing food—a find that stands to upend scientists' preconceptions about one of the Americas' most iconic big cats.
“For more than 60 years of intensive research... we have said that [cougars] are solitary, robotic killing machines,” says Mark Elbroch, lead scientist for the Puma Program at Panthera, the global wild cat conservation organization. “Instead, what we have unveiled is a secretive animal with a complex social system completely built on reciprocity.
“That flies in the face of everything we ever thought about this animal,” he adds.
“I thought it was really exciting research—we usually assume that these animals aren't social,” adds Justine Smith, a postdoctoral researcher at the University of California, Berkeley, who studies humans' impacts on cougars. She was not involved with the study.
According to Elbroch, his team's discovery—published on Wednesday in Science Advances—was as much a matter of technology as it was patience. For years, he says, he and other researchers had seen tantalizing glimpses of cougars crossing paths, but they couldn't see or understand the interactions.
That all changed when Elbroch, a National Geographic conservation grantee, installed a network of camera traps across nearly 900 miles of the Greater Yellowstone Ecosystem, with the hopes of catching cougars in the act. (Explore Yellowstone as never before in our May 2016 issue.)
Initially, Elbroch's camera network wasn't looking for signs of mountain-lion society; that was a happy accident. Originally, he just wanted to know what cougars were eating, so he could better estimate their caloric intake and impact on the ecosystem. On this question alone, the camera traps yielded gems: In a recent paper in Biological Conservation, Elbroch showed that the highest diversity of scavengers ever recorded on Earth exists at cougar kill sites.
But nothing prepared him for a moment in early 2012, when he stumbled across an extraordinary sight while reviewing camera-trap footage: an adult female cougar approaching the carcass of an elk another female cougar had killed.
The two hissed and struck postures at one another—and then, to Elbroch's shock, the kill site's cougar let the new arrival share her meal. This generous act was no mere fluke; the pair of cougars stayed in each other's company for a full day and a half. And as later genetic data showed, they weren't related to one another.
In effect, Elbroch's camera had captured the first cougar friendship known to science.
“It just sort of shattered everything we thought we had learned about the species,” he says. “I remember throwing my hands up in the air.”
At first, Elbroch thought that what he had witnessed was extraordinarily rare. But once he started focusing on the behavior, he was in for a second surprise: The first footage wasn't as uncommon as he thought it'd be. Between 2012 and 2015, Elbroch's cameras had recorded 118 interactions between two cougars. A full 60 percent of them were at kill sites—and many were the sort of meal-sharing he had seen before. (Meet the elusive wildcats you've never heard of.)
Over and over, Elbroch saw cougars “give” other cougars access to their kill sites. In later encounters, the second cougar would be 7.7 times more likely, on average, to return the favor.
The data that Elbroch's team obtained not only let them capture these relationships on film, but also help them draw maps of cougar society. Which cougars were hanging out with one another most often? Who visited whom?
In partnership with Mark Lubell and Michael Levy of the University of California, Davis, Elbroch mapped the cougars' relationships as a tangle of interconnected nodes. The team could then mathematically quantify how interconnected any one cougar was within the social group.
The data revealed that cougar society not only existed, but it was hierarchical. The boundaries of various social groups mapped closely to the territorial ranges of individual males. Female cougars with ranges overlapping the same male's range were more likely to socially interact than if their ranges didn't “share” the same male.
In other words, male cougars seem to play an outsize role in cougar society, a role that Elbroch likens to that of a territorial governor.
“Lots of folks have intuitively understood that males must be important to the social organization of mountain lions, [but] no one really knew how,” says Elbroch. “What's cool is that we've actually done fancy math and statistical analysis very clearly why males are important in the social organization of mountain lions.”
Impacts of Hunting?
For all the insights that the paper provides, other research will need to confirm whether other cougar populations elsewhere in the Americas have strong social lives.
“I would love for more work to be done, to see how generalizable this is,” says Smith. “There might be some sort of necessity—maybe the size of the prey, or how available they are—[that would make this population] want or need to engage in this sort of network.”
It's also unclear how trophy hunting of cougars might affect the newly discovered cougar society, since none of the cougars Elbroch studied were killed by hunters during the observation period.
Elbroch hypothesizes, though, that removing a male from a cougar population may lead to social upheaval—potentially informing how wildlife agencies approach management of the species.
“If it is creating social chaos, what are we doing to do?” says Elbroch. “Do we allow trophy hunting to continue? Do we adopt new strategies?”