CSI: Puma Country

They call us “wildlife ecologists” but we are crime scene investigators, of sorts. Every day we log new victims, studying their twisted remains for clues about who they were and how they died.

The Clues

Given the general shape of the remains and our location in the Andes, if the body is large with a dark brown tail or brow, it’s a guanaco. If it’s small and sand-colored, it’s a vicuña.

The shape of the pelvis tells us whether it was male or female; the tooth wear along the bottom jaw gives us its age. The color of the marrow in the thigh bone tells us whether it died fat and strong, or thin and weak. And tell-tale signs on the carcass and all around it—skull punctures, bruising on the neck, blood splatter on the rocks, marks of struggle in the sand—help us name the final cause of death. Almost always, the killer was a puma, lunging claws-first from its hiding place, clamping to the victim’s neck, and holding on until the kicking and the breathing stop.

Each day our research team records the species, sex, and age of several puma-killed vicunas and guanacoes. Photo by Arthur Middleton.
Each day our research team records the species, sex, and age of several puma-killed vicunas and guanacos. (Photo by Arthur Middleton)

The Setup

I’m back at San Guillermo National Park in Argentina for the southern summer, following the pumas we collared last year. I work with three others: Emiliano Donadio, of Argentina’s national research council, plus two field assistants, Mikael Cetjin and Laura Rollán.

Once a week we download a fresh set of GPS locations from satellite collars on the pumas, then we map every instance of multiple GPS locations within a 20-meter radius. These location clusters represent potential kill sites. Each morning, we plug some of the clusters into our GPS units and set out on foot to visit them.

On some days we hike miles into the hot, still air of the San Guillermo plains. On others we scramble, breathless, up the park’s windy mountainsides. Often, all we find is a place where a puma shaded up for a nap. But sometimes we find a victim’s final resting place. If the kill is fresh—a day or two old—we may be welcomed by three dozen condors, bursting off the ground in sudden bedlam.

This guanaco met its end in the jaws of a puma while the rest of us were celebrating the New Year. (Photo by Arthur Middleton)

This method of finding kills—“cluster searching”—is a relatively new way to study the feeding habits of big predators. From the savannas of Africa to the boreal forests of Scandinavia and the mountains of the Americas, biologists are coupling high-tech satellite tracking with old-fashioned, boots-on-the-ground field work to see deeper into the lives of lions, wolves, bears, and pumas. Kill by kill, we build a picture of where the predator hunts and which prey animals it hits the hardest.

These morbid data help us understand why prey numbers fluctuate, why prey behave the ways they do, and what it all means for the ecosystems they inhabit.

The Findings

So far, the method is working beautifully at San Guillermo. In two months of late 2014, the team found 76 kills made by five collared pumas. If early patterns hold, it seems the cats prefer to kill the larger guanaco, even though a guanaco is harder to come by than a vicuña. It also appears that pumas prefer to hunt in the grassy meadows and rocky canyons even more strongly than we thought—we find the majority of their kills are in those places. As masters of the surprise attack, this is where they are at their deadliest.

A day’s work following San Guillermo’s pumas is not without its challenges. The thin air and dry heat of this desert at nearly 12,000 feet in elevation limit how long and how hard we can work. And the unbelievable preponderance of kills lying around on the landscape—we often find new carcasses are piled atop older ones—can confuse matters once in a while. But when each kill sheds new light on the lives of these high mountain pumas, and each day takes us somewhere new in this wild place, we have no complaints.

The end of a cluster-searching day at San Guillermo, with afternoon storms in the distance. Photo by Arthur Middleton.
The end of a cluster-searching day at San Guillermo, with afternoon storms in the distance. (Photo by Arthur Middleton)

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Meet the Author
Arthur is a wildlife ecologist based at Yale School of Forestry and Environmental Studies. He studies the predator-prey interactions and seasonal migrations of large mammals in the Rocky and Andes Mountains.