The puma family took biologist Mark Elbroch by surprise. They were supposed to be a ways off. But here they were, year-old kittens, bungling the final moments of a baby mule deer's life in a matted-down circle of grass as the mother mountain lion looked on.
Elbroch, the puma program director for Panthera, saw a rare opportunity to capture on film what biologists call "operant learning." So he set up the remote cameras he had in his backpack, and he waded back into the hip-high grass of western Wyoming and out of sight.
What unfolded on film over the next 25 minutes confirmed that "mountain lions take a long time to become efficient killers," Elbroch says. Even at a year old and each outweighing the fawn by 50 pounds or more, he says, "They're just clueless."
They still hadn't dispatched the screaming fawn when the kittens dragged it off camera. "It's horrific to watch," Elbroch says.
It turns out that, as pumas learn to hunt throughout their lifetimes—even long after they've left their mothers' sides—it affects their choice of prey.
This discovery, reported March 29th in the journal Conservation Science and Practice, potentially calls into question the assumption that allowing hunters to kill more pumas will translate into more of the elk and mule deer that human hunters prize. This assumption has led to recent decisions to increase hunting of mountain lions in the western United States.
Elbroch and his Panthera colleague, Howard Quigley, pulled together data on 13 GPS-collared pumas between April of 2012 and January of 2016 from the organization's long-term Teton Cougar Project based near Jackson, Wyoming. They then modeled the data to gauge the influence of different factors, such as age, elevation, and the animal's sex, along with various combinations of these variables, on the prey these individual animals went after. The results of the analysis, Elbroch says, were "incredibly simple."
"As pumas get older, they tend to select larger prey," he says. And the reason for that is equally straightforward.
"It takes time to learn how to take down monstrous animals that are eight times your size," Elbroch says. Mountain lions "risk their lives every time they jump on the back of something big."
Young cougars typically go after small prey like hares, raccoons, and grouse. With age, they graduate to killing mule deer and then to specializing on elk, the most common preference among the cats in the study and the one favored by the oldest animals.
Those results suggest that recent moves to increase the numbers of sought-after trophy species of herbivores like mule deer might be ill-advised and counterproductive. Colorado Parks and Wildlife, the state's game agency, has embraced a "predator control" strategy involving the hunting and trapping of up to 15 pumas and 25 black bears a year with the goal of boosting a flagging mule deer population in the state's northwest corner. The deer's meat and the males' antlers make it a favorite quarry of hunters, and Panthera said pressure from hunting groups helped set this plan in motion.
But earlier research in Idaho demonstrated that taking pumas (and coyotes) out of the equation didn't help local mule deer populations grow, even though more females and fawns survived. Another study revealed a correlation between sustained puma hunting and a younger puma population, as hunters seek out and kill the oldest and largest cats. The upshot of that finding, taken together with this new study, is that killing more pumas might actually increase the proportion of the population that specializes in mule deer, which are smaller and easier to bring down than elk, Elbroch says.
"The conclusion that unintended consequences are possible is a really important one," says Kyle Knopff, a wildlife biologist with Golder Associates in Calgary, Alberta.
Knopff, who was not involved in this study, notes that 13 animals is a small sample size that makes it difficult to draw more specific conclusions, and agrees with Elbroch's view that the results warrant further testing with more mountain lions over longer time periods. Knopff also notes the "incredible amount of effort" that such research would entail.
In 2010, Knopff, then at the University of Alberta, and his colleagues published a study in The Journal of Wildlife Management that examined the prey selection of more than 50 pumas in Alberta. Among their most significant findings was the notion that individual puma prey preferences varied, with male pumas, which are much bigger than females, going after large game like moose.
But, Knopff adds, more research is needed to confidently say that puma hunting will or will not increase populations of ungulates, the hoofed mammals that include elk, deer, and bighorn sheep.
"In some systems that may be true," he says. "In others, it's clearly not."
"In my view, the actual scientific conclusion is that we need to be very careful how and under which circumstances we harvest predators if our intentions around predator management are to have some certain outcome for ungulate populations," Knopff says.
"The take-home message here is that it does matter what animals you remove from the population," says John Laundré, a cougar biologist at Western Oregon University.
Laundré says Elbroch's study supports what researchers have been saying about predator-prey relationships for decades.
"It's not the predator that determines how many prey there are," Laundré says. "It's the weather, how much food, how cold it gets, how hot it gets, all these types of things."
Indeed, many scientists blame protracted droughts across the western U.S., not pumas or other predators, for diminished mule deer numbers.
Still, reining in predator populations remains a favored wildlife management strategy at agencies across the West. Elbroch says it's important to note that legal hunting in its current form across the western U.S. and Canada won't wipe out pumas. Wildlife managers "have done a super job of maintaining mountain lions on the landscape."
But, he says, "I do believe that hunting is the greatest threat to the stability and the ecological function of mountain lions."
In a recent study, Elbroch and his team made the case that mountain lions are "ecosystem engineers" because the carcasses they leave behind provide food and habitat for a wide range of other creatures. The researchers found 215 species of beetles in prey animals killed by mountain lions.
While current management strategies ensure that cougars persist in the West, these approaches don't account for the "unintentional effects" of hunting, Elbroch says. In his view, that calls for a "move away from the numerical assessment" of mountain lions.
"Numbers are not what build populations. Individuals build populations," Elbroch says. "Mountain lions are individuals. We need to recognize that."
This story originally appeared at the website of global conservation news service Mongabay.com. Get updates on their stories delivered to your inbox, or follow @Mongabay on Facebook, Instagram, or Twitter.