North American Cougar, puma or mountain lion
A juvenile mountain lion walks at night in Aptos.
(Courtesy Sebastian Kennerknecht)
Environment

‘The landscape of fear’: Big cats pay a price for avoiding areas now inhabited by humans

Mountain lions burn a lot of extra calories when they are trying to navigate highly developed areas. To save precious energy, male lions reduce their range dramatically, according to new research from UCSC.

New research from UC Santa Cruz scientists found that mountain lions go to great lengths — and burn a lot of calories — trying to avoid human contact.

Because this is taxing and stressful for animals with such high caloric needs and forces them to limit how far they roam and hunt, scientists worry that this dynamic might eventually make them an endangered species.

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“They can’t just keep ramping up how many deer they’re killing and eating incessantly,” says scientist Chris Wilmers. “At some point, they have to adjust and in this case they adjust by moving less. At a certain point too they’re going to be unable to persist because they literally can’t feed themselves despite moving less.”

The work, which was published recently in the Proceedings of the National Academy of Sciences, has implications for local development and conservation.

Wilmers, a professor of environmental sciences at UCSC and the leader of the Puma Project, a research group that studies pumas in the Santa Cruz Mountains, has been fitting lions with GPS collars for years.

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But for this study, which was led by Barry Nickel, the director of UCSC’s center for Integrated Spacial Research, he and his team also equipped mountain lions with accelerometers — basically FitBits for big cats — in order to track not only their overall movements but also their calorie expenditure.

The goal was to compare “the physical landscape to what we call the landscape of fear,” Wilmers said, his term for the human activity and development that lions do their best to avoid. “We represent the landscape of fear basically by housing density, because we’ve shown in previous [work] that mountain lions are scared of us, and housing density does a pretty good job of representing the landscape of fear that these animals face.”

Wilmers and his colleagues set out to determine the caloric cost the animals spend trying to avoid people. A major hurdle to overcome was calibrating the accelerometers to be able to measure how many calories the pumas were burning, which involved getting mountain lions to walk on a treadmill.

“We had a vet in Colorado that had a couple of captive mountain lions, and she sort of took [calibration] on as a project to see if she could do it,” Wilmers said. “But it’s easier said than done with certain animals. Especially cats.” Eventually, the Colorado veterinarian got in enough mountain lion treadmill time that Wilmers felt confident in the calibration.

Then the scientists placed collars containing GPS sensors and accelerometers on five female and eight male mountain lions, and observed them for two months. Analysis of the resulting data found that in highly developed areas, the lions greatly reduced their movements in order to conserve energy, because avoiding humans was so taxing for them.

Nickel and Wilmers estimated that pumas expend 13 percent more calories per five-minute period in habitats near or in human development than they would in more remote wildland habitats, and as a result, the male pumas especially reduce their range. The scientists found that the males in the most developed habitats had 78.8 percent smaller home ranges compared to those with the most remote home ranges.

Tracking data for four pumas.
Tracking data for four male pumas shows a stark difference in the total
home range area covered by pumas in habitats with the highest housing
density (purple and brown tracks) compared with those in wildlands
(yellow and blue tracks).
(Barry Nickel et al. PNAS 2021)

Locally, Wilmers pointed to the area between Highway 17 and Nisene Marks, around the summit, and the San Lorenzo Valley as places were pumas spend a lot of energy navigating the “landscape of fear.”

“Pretty much every house in those places is in mountain lion territory,” Wilmers said. “It’s not at the edge, it’s in it.” The most undisturbed areas in Santa Cruz County are the North Coast between Wilder Ranch and Big Basin.

Wilmers said the team’s research underlines the importance of “big, undeveloped areas of open space,” in maintaining mountain lion populations. He hopes for future development to be focused on making cities denser, and not spreading out further into undeveloped areas.

Santa Cruz County does contain healthy habitat for mountain lions, Wilmers said. “The Santa Cruz Mountains, in general, we’ve done a great job,” he said. “But that’s because we’ve been incredibly vigilant in protecting these places. It’s not a done deal.”