“Never say you can’t train a cat,” is what a researcher said after taking ten months “and a lot of meat” to train “Rascal” and other captive mountain lions to walk on a treadmill. The cooperation of the felines helped scientists understand how wild mountain lions burn energy and explained why the big cats’ use of the ambush method to catch their prey works so well for them.
The puma, the Western Hemisphere’s most widely distributed mammal, is rarely seen. But its stealth may explain how the cat manages the high-energy costs of its carnivore lifestyle, a new study based in part on teaching a puma to run on a treadmill shows.
The highly adaptable puma can live in most any American habitat, from alpine forests to swamplands, and goes by names as varied as the places it once roamed. But “ghost cat” best captures the American lion’s secretive nature, which challenges researchers studying its habits to develop increasingly clever methods of doing so.
Among the most basic questions biologists want to answer is how pumas manage the energetic costs of hunting and killing prey at least twice their size. And now, a team of biologists has managed what some thought impossible – training a puma to run on a treadmill – to show how the big cat’s ambush-hunting strategy helps it conserve enough energy to survive.
The group, led by Terrie Williams and Chris Wilmers of the University of California, Santa Cruz, spent years working with engineers to develop a novel wildlife tracking collar to measure the energetics, movements and behaviors of animals in the wild. Energetic expenditure is the lifeblood of an animal, says Wilmers. “If they’re burning more calories than they’re consuming they’ll die. And without enough surplus calories, they’ll never reproduce successfully.”
But biologists didn’t have a direct way to continuously monitor energy costs. So Williams and Wilmers developed their SMART (species movement, acceleration and radio tracking) collar, which tracks location with a global positioning system and measures movement-generated forces with an electronic accelerometer.
To translate the accelerometer’s output into energetic costs, the team needed to know what the animal was doing to trigger the patterns and how much oxygen it consumed. That meant training a puma to run on a treadmill.
Williams had no illusions about doing such a thing with a wild puma. But after years of putting wolves, water rats and even river otters on treadmills, she thought surely she could do the same with a captive puma. But her colleagues at zoos and wildlife facilities thought she was crazy.
There’s a reason you don’t see pumas performing tricks in shows, zoo experts told Williams. Everyone insisted they wouldn’t tolerate a collar and certainly wouldn’t go on a treadmill because they’re impossible to train, she says. “It took three years for me to get to somebody who was even willing to put a collar on a captive puma.”
Finally, Williams found Lisa Wolfe, a veterinarian with Colorado Parks and Wildlife who had raised three pumas after their mother was killed. Williams asked Wolfe, a skilled animal trainer, if she’d be willing to put a collar on her cats. Wolfe quickly agreed.
“Never say you can’t train a cat.”
“After she got the collar on, I dropped the bomb about the treadmill,” Williams says. Wolfe, who’d run bighorn sheep on treadmills for a previous study, embraced the challenge. It took 10 months and “a lot of meat,” Williams says, “but once they knew what the game was, they were brilliant. Never say you can’t train a cat.”
The team collected data from the collar while videotaping the treadmill sessions, to match each behavior to the accelerometer’s patterns. A Plexiglas box around the treadmill was connected to an oxygen analyzer, which measured how much oxygen cats used for everything from rest to running, so the team could determine how many calories each behavior burned.
The collared cats were also videotaped as they pounced, groomed and lazed about in an outdoor enclosure. The setup mimics Fitbit monitors, though they calculate energy use based on years of oxygen measurements taken as people of all sizes run on treadmills.
“We had to develop the equations for a mountain lion,” Williams says. With a library of accelerometer signatures to match the energetic costs of a wide range of behaviors, the team could interpret the data they’d been collecting on the wild pumas that Wilmers and his team had collared in California’s Santa Cruz mountains. What they found opens a window on the predatory behavior of large cats in the wild.
On a typical hunting day, pumas take about two hours to hunt, stalk and kill their prey. While GPS tracks have been used to estimate energy costs, they can’t reveal how much energy carnivores need to move through rugged terrain or overtake different-sized prey, so biologists used indirect methods.
The costs of hunting, it turns out, are more than twice the amount typically assumed in carnivore energetic models. All the adjustments an animal makes to run uphill, jump across rocks and pursue prey takes a toll. But evolution appears to have equipped pumas with the hunting skills to offset the high costs of carnivory. Cats who revealed their presence – unwisely abandoning the ambush strategy that relies on waiting patiently out of sight before striking – burned more calories than their stealthier counterparts.
This covert hunting strategy likely helps them conserve enough calories to reproduce, Wilmers says. But the traces of their accelerometers revealed another energetic trick. Wilmers and his team identified likely kill sites by the clustering of GPS signals, suggesting a cat was feeding. Then they visited the sites to measure the weight and size of the prey, to see if energy costs varied with prey size. When they matched the accelerometer signatures to the carcasses, it was clear that pumas saved their most powerful pounce for their biggest prey.
“This is an exciting leap forward in quantifying the energetic expenditures of wild mountain lions,” says Mark Elbroch, who directs the Teton Cougar Project and was not involved in the study. He thinks it will help biologists test the energetic limits for cats and other carnivores coping with diverse human and ecological stresses to better understand what they need to survive.
Williams says the findings suggest that pumas have evolved the most economical way to survive and reproduce. “But we’ve made it harder and harder for them to do that.” We’re just learning what it really takes to be a lion in the wild, she says. If pumas are living on the energetic edge, human activities that destroy the vegetation they use for cover while hunting or reduce prey abundance could threaten their survival.
The team plans to use their collar to study how land use and prey density affect the energetics of pumas and other carnivores. “Large carnivores are declining all over the world,” says Wilmers. “If we can better understand how human activity impacts their energetic balance, we can hopefully do a better job of conserving them.”