Mountain lions, or pumas, have long inhabited the undeveloped lands in and around Stanford. Though rarely seen, the elusive cat occasionally leaves tantalizing clues of its presence—like the fresh paw prints found near the campus golf driving range in January.
Now, Stanford researchers have obtained visual proof that mountain lions regularly roam through University lands.
The evidence comes from a network of 19 remote cameras strategically placed in Jasper Ridge Biological Preserve, Stanford's 1,189-acre field research site five miles west of the main campus. Since 2009, cameras have captured more than 40 photos and two brief videos of mountain lions making dusk-to-dawn forays.
"Over the years, we've seen a number of deer kills in the preserve, so we assumed that mountain lions were coming here, maybe every few months," says Trevor Hebert, GIS and data manager at Jasper Ridge. "But when we started getting weekly and even daily photos of lions on major trails, that was a surprise."
In 2006, biology professor Rodolfo Dirzo and colleagues installed the first generation of camera traps in undisturbed areas of the preserve. In 2 ½ years they recorded more than 15,000 photos of animals—from coyotes to bobcats to humans—but no mountain lions.
Hebert began installing a new camera network in October 2008, this time along open trails and dirt paths. Instead of triggering a visible flash, these cameras use infrared sensors that detect changes in body temperature when an animal moves, then transmit the digital image wirelessly to the Jasper Ridge servers.
The results were dramatic. On September 10, 2009, an infrared camera captured a black-and-white photo of a solitary puma at night; two more lion photos were taken that year. After a lull of months, cameras recorded 30 lion photos on 28 days between May and September 2010, with peak activity between sunset and sunrise. Hebert suspects that the same lion was photographed many times, occasionally at the exact spot where researchers had been doing fieldwork hours earlier. Several photos were shot less than a mile from Jasper Ridge headquarters.
"While it was exciting to discover that mountain lions are an integral part of the Jasper Ridge ecosystem, the photographs also raised questions about the safety of our field researchers, who sometimes work alone on and off the trails," says Jasper Ridge faculty director Chris Field, PhD '81, professor of biology and of environmental earth system science.
Photo: Jasper Ridge Biological Preserve
In response to the sudden spike in puma pictures, Field and other members of the Jasper Ridge advisory committee recommended a full review of mountain lion policy at the preserve.
The timing couldn't have been better. In spring 2010, Jasper Ridge docent Margaret Krebs had approached staff scientist Nona Chiariello about partnering with the Woods Institute for the Environment on a pilot project called the Rising Environmental Leaders Network.
"The goal of the project was to provide Stanford postdoctoral researchers and graduate students an opportunity to practice their communication skills by framing a real-world environmental problem and presenting their solutions to a decision-making body," explains Krebs, program manager at the institute's Leopold Leadership Program.
Chiariello, PhD '81, invited the postdocs and grad students to review the mountain lion images and advise Jasper Ridge on policies, procedures and opportunities for research and community outreach. Five volunteered to serve on the consulting team: graduate student Lena Perkins, MS '07 (mechanical engineering) and postdocs Kye Epps (soil science), Steve Litvin (marine ecology), Scott Loarie, '01, MS '02 (landscape ecology) and Mike Papenfus (economics).
Nicole Ardoin, a member of the Jasper Ridge advisory committee, served as faculty lead on the project. "This was a test case—an opportunity to engage faculty, postdocs and graduate students in project-based learning with a risk assessment/management component," explains Ardoin, assistant professor of education and center fellow at the Woods Institute.
A 1-IN-10-MILLION RISK
In September 2010, the Woods Institute and Jasper Ridge brought together mountain lion experts, Stanford faculty and staff, and the student consulting team for a two-day workshop. After conferring with the experts, conducting a statistical analysis of the lion photos and reviewing the historical record of human-lion interactions, the students drafted a 50-page assessment of mountain lion management and policy options at Jasper Ridge.
They first considered how many lions regularly roam through Jasper Ridge. "Current camera-trapping data suggest that mountain lions are present on the preserve about 24 percent of the time," they wrote. However, "there are likely at most only one male, one female and possibly several cubs whose territory includes the preserve."
A male puma can weigh 200 pounds and make a horizontal leap of 30 feet onto a deer. But are these powerful carnivores a threat to humans?
"Based on statewide historical data, the annual risk of a mountain lion attack on a person [at Jasper Ridge] is estimated to be 1 in 10 million," the team concluded. "To put this in perspective, the annual probability of lightning striking someone on Jasper Ridge is 250 times greater than an attack by a mountain lion."
California state records confirm 15 mountain lion attacks and six fatalities since 1890. Yet hundreds of lions have been killed, legally and illegally, during that period. In 2004, police shot and killed a lion that wandered into a residential section of Palo Alto. In September 2010, police fatally shot a female lion in Berkeley, and last March, a state game warden killed another female in Redwood City nine miles from Jasper Ridge.
PUMA COUNT: 2010 sightings in San Mateo County (blue, Jan.-Mar.; green, Apr.-Jun.; yellow, Jul.-Sept.). (Photo: Courtesy San Jose Mercury News)
"The perception is that if it's dangerous, shoot it," says report co-author Papenfus. "But mountain lions have been at Jasper Ridge forever, and there have been no negative interactions with people."
Although the risk of a lion-human encounter is extremely low, the report recommended a series of safety protocols for staff and visitors that have been adopted elsewhere. Among them:
• Work in groups of two or more from dawn to dusk.
• Avoid crouching when doing fieldwork.
• Fight back in the unlikely event of an attack.
• Post signs—such as, "Private Property, No Trespassing, Mountain Lion Habitat"—along the perimeter fencing of the reserve.
KEEPING OUR BALANCE
The images captured so far have provided a trove of data for ecologists and other researchers. For example, Hebert detected a seasonal pattern of lion activity, with more visits occurring during the dry season from May to September.
"One of the very encouraging things about all of the mountain lion pictures is that we know that we essentially have an intact ecosystem with the top predator actively killing deer," Hebert says. "We weren't always sure that was the case."
According to the student report, the confirmed presence of mountain lions in the preserve opens numerous opportunities for research, education and conservation.
"The Jasper Ridge photos could be used to inform the public about the important ecological role of mountain lions and the need to protect their shrinking habitat in the Bay Area," says co-author Litvin. "Mountain lions help control the deer population, and deer eat a wide variety of plants. Too many deer could have a negative impact on the entire ecosystem."
LION'S SHARE: The top predator in the local ecosystem helps keep the deer population under control. (Photo: Jasper Ridge Biological Preserve)
To help build positive awareness of living and working in lion habitat, the authors recommended that Jasper Ridge engage local communities in mountain lion research. For example, staff could develop an interactive website where people outside the preserve could post real-time information about lion activity. Co-author Loarie recently launched a website called iNaturalist that allows Jasper Ridge docents to post sightings of animals and plants.
To assess puma abundance in Jasper Ridge more accurately, the student team proposed several long-term research initiatives, including collaboration with the Bay Area Puma Project and other groups that use satellite-transmitting collars to track individual pumas in the Santa Cruz Mountains.
"I'd love to see additional research on how mountain lions interact with other species," Perkins says. "The more we can learn, the better equipped we'll be to manage lions in a prudent way and keep a healthy population in the Bay Area."
The Jasper Ridge advisory committee has begun implementing some report recommendations, such as adopting measures to raise awareness of mountain lions among Jasper Ridge users, and switching from infrared to near-infrared cameras to obtain higher quality images. "It was really an inspired idea to bring such highly qualified graduate students and postdocs together to quickly gather useful information for the committee," Hebert says. "From the faculty perspective, this project has been a complete success," adds Ardoin.
Epps agrees. "This experience succeeded in giving lonely, isolated postdocs like me an opportunity to connect with other professionals I don't routinely interact with." Although Epps has never seen a mountain lion, she has grown to respect the ability of this remarkable animal to persevere, both at Jasper Ridge and throughout the Bay Area.
"We humans present a greater risk to mountain lions than mountain lions present to us," she says. "Greater knowledge of how they move about can really help us to plan wisely so that we can keep both humans and mountain lions safe."
Mark Shwartz is a communications/energy writer at the Precourt Institute for Energy at Stanford.
