Why Do Adult Cougars Kill Each Other?

Portrait of F51, an adult female mountain lion, tracked by the Teton Cougar Project in northwest Wyoming. Photograph by Mark Elbroch / Panthera

F51, an adult female mountain lion currently tracked by Panthera’s Teton Cougar Project, meandered towards the eastern edge of her range, her two female offspring bouncing like electrons in orbit around her. Who can say what a mountain lion thinks, but from our perspective, life seemed good for F51.

The family had fed off a series of elk in quick succession, and then successfully dodged the local wolf pack that stole her last kill from them. Her kittens were fat, healthy and growing fast. How quickly things can change.

M85, an adult male also tracked by the project, sat on his kill at the base of spectacular red cliffs, content to move little and eat more. He heard F51’s approach—he likely heard the kittens—as she dropped through a narrow cleft in the rocks above his position, and he set out to intercept them. This much was clear, written out in the snow, but the next part involves some speculation.

Perhaps M85 approached aggressively, or perhaps F51’s kittens were exposed in front of her, but whatever the scenario, she engaged him. The pair met in a storm of claws and fury, packing the snow as they rolled and wrestled. They slid down the hill about 15 feet, packing another circle of snow and leaving behind great tufts of fur. Down they slid even further, to tumble and roll yet again, the first sprinkles of blood shining ruby red on the untouched snow.

Then there was a last great tumble, the pair locked tooth and claw as they slid fast and slammed into a young fir tree; the lowermost branches were snapped off in the violence. Blood and fur soaked and covered the area at the base of the trunk, where they lay long enough that their entwined bodies melted into the snow. And then she was dead, this magnificent animal, this mother of two.

M85 dragged her another 20 feet before he left her. He returned to feed lightly from her carcass, but shortly after, abandoned the area completely. The kittens fled at the first signs of trouble, but are still hanging about the area, now four days later. At seven months old and without a mother, their futures are uncertain, if not bleak. Kittens typically need to be older than a year in order to survive on their own.

F51, an adult female mountain lion, hisses to defend her food from another female that is trying to share in the kill. Photograph by Mark Elbroch / Panthera.
F51, an adult female mountain lion, hisses to defend her food from another female that was trying to share in the kill. Photograph by Mark Elbroch / Panthera.

Intraspecific killing (“intra” meaning “within” and “specific” referring to species) is a scientific descriptor for an animal that kills another animal of its own kind. When it’s humans and premeditated, we call it murder, but for other mammals, we use varied vocabulary to describe killing for reasons other than food. Interspecific (across species) competitive killing is killing another species for competitive reasons, intraguild predation describes a predator that kills another predator, and infanticide describes adults that kill young animals of their same species. Regardless of the terminology, we’re talking about death.

The horrific battle between F51 and M85 stretched 60-70 feet and was painted with blood. But as one fascinated with mountain lion social behaviors, what I really wanted to know was why it happened. And the larger question, or course, is whether solitary cougars are always so aggressive towards each other. These are the questions Panthera is trying to answer.

Cooley et al. (2009) proposed that infanticide of cougar kittens by adult males increases in hunted population, where there is regular male turnover. In fact, in this case, M85 was west of his usual haunts and in an area typically defended by M29, the resident male that had been legally killed by a hunter several months earlier. M29’s territory has remained open, and in his wandering M85 encountered F51, who we believe he’d never met before.  This might offer a partial explanation.

F51's kittens, playing. Photographs by Neal Wight / Panthera.
F51’s two kittens, playing. Photographs by Neal Wight / Panthera.

But is it common for cougar clashing to result in the death of one or the other? According to 13 years of research: yes and no. Yes, in that we have documented mountain lions killing other mountain lions of every age category. Over 13 years, the Teton Cougar Project has documented two of 68 kittens between zero and 18 months of age that were killed by other mountain lions, and two more that were killed by an unidentified predator, which might have been mountain lions. Three of 16 subadults that died or disappeared between the ages of 18 and 30 months were killed by other cougars, and now five of 36 adults we’ve tracked (two females, three males) were killed by their own kind. So yes, it happens. But it’s also rare.

Our more recent research has revealed that adult mountain lions interact with far greater frequency than we ever imagined, and that only five to 10 percent of interactions involve aggressive physical contact. In fact, F51 shared a meal with an adult male while she was still lactating in the fall, and just several weeks before her death she interacted with another adult female around a kill for several days.

Mountain lions, we’ve found, are surprisingly tolerant of each other. This makes F51’s death even more mysterious. One theory behind infanticide is that it creates future mating opportunities for the male killing the kittens, but why a male would kill an adult female is more difficult to explain with biology. Thus, we expect it had something to do with defending her kittens.

F51 was an icon for the Teton Cougar Project. She was the star of National Geographic Wild’s American Cougar as a young adult, and since has provided us insights into cougar social systems, movements, and fecundity (see fecundity, a previous blog in which she is described). Her loss is a blow for the project, but one we will weather with time. Such is often the lot of the biologist, to bear witness, document, and learn.

Will F51’s kittens survive on their own? Will the unmarked female we’ve glimpsed several times this winter in F51’s range, set up residency there? Will a new male move in to fill M29’s territory, or will M85 migrate west? And if he does, will his movements disrupt existing social relations and families? There are still so many questions.

Peruse old photos and videos of F51 and new posts about other cougars on the Teton Cougar Project Facebook page.

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Cooley HS, Wielgus RB, Koehler GM, Maletzke BT (2009) Source populations in carnivore management: cougar demography and emigration in a lightly hunted population. Anim Conserv 12:321–328.



Meet the Author
Mark Elbroch is Director of the Puma Program for Panthera, a US-based non-profit that conducts science and conservation action to promote wild cat conservation worldwide. He has contributed to puma research in Idaho, Colorado, California, Wyoming, Mexico, Washington and Chile. He earned his PhD at the University of California, Davis, where his dissertation research focused on puma ecology in Patagonia in the presence of endangered humeul deer. He has authored/coauthored 10 books on natural history (http://www.amazon.com/Mark-Elbroch/e/B001ILHI96) and numerous scientific articles published in peer-review journals.