Wolves are coursing, social predators that operate in packs to select disadvantaged prey in open areas where they can test their prey’s condition. Mountain lions are solitary, ambush predators that select prey opportunistically (i.e., of any health) in areas where slopes, trees, boulders, or other cover gives them an advantage. Thus, wolves and cougars inhabit and utilize different ecological niches, allowing them to spatially and temporally coexist; nevertheless, in the absence of wolves, cougars utilize areas traditionally assumed to be the sole dominion of coursing wolves. This suggests that where wolves are sympatric with cougars, wolves limit mountain lions.
In fact, wolves kill mountain lions. This has never been disputed. Wolves are considered the dominant competitors in most interactions between the species. Take for instance, the Hornocker Institute study of mountain lions in Northern Yellowstone led by Dr. Toni Ruth, in which researchers discovered the remains of three mountain lions killed by wolves. What is contentious is the idea that mountain lions might kill wolves.
Liz Bradley, a Montana Fish, Wildlife and Parks wolf biologist, reports that she has discovered five wolves killed by mountain lions in three years—all bearing the characteristic canine punctures in their skulls betraying the identity of the perpetrator. Some dispute her claims and point out that wolves fight each other too, especially adjacent packs, and that they also attack the head; skeptics believe a canine puncture in a wolf skull could be made by another wolf just as easily as a mountain lion.
The Teton Cougar Project operates in the Southern Yellowstone Ecosystem, and is one of very few long-term studies of mountain lions. Since the start of the project, wolves have trickled into the area, established territories and reproduced. In 2001, U.S. Fish and Wildlife Service surveys estimated that there were about 10 wolves in our study area, and that number steadily increased to as high as 91 in 2010. To date, we’ve documented five lions killed by wolves, all kittens, and all less than six months old while they were still relatively slow to climb and less than fully coordinated. But it was just last October that we finally documented the contrary. For the first time, a mountain lion we were tracking killed a wolf.
She’s a particularly feral mountain lion, F109, an adult female with three three-month-old kittens. All cougars are feral, of course, but there’s something unique about F109. She has “crazy” eyes, and always wanders the most rugged, inhospitable terrain. She was near impossible to catch in the first place. She’s a survivor.
We can’t tell you exactly what happened, but we can describe what we deciphered from the clues left behind in the snow. F109 was up high traversing steep, barren slopes, where we expected there was little game. Nevertheless, her location data indicated that she’d stopped and we suspected she’d made a kill. We slogged up the mountain to investigate, the ground bare of snow adjacent the road, but as deep as our thigh in the high bowl where she lingered. The entire area preceding her position was a mosaic of wolf tracks and trails. A wolf pack made up of adults, subadults and pups had criss-crossed the area, leaving barely a patch of snow without their sign.
Perhaps the wolves had challenged F109, or perhaps just one of them wandered too close to her kittens, or perhaps a pup felt like exploring on its own—trying to decipher the absolute pandemonium of tracks was beyond us. Whatever the circumstances, F109 captured and killed a pup born this year just above the chaos of wolf activity. By this time (November), wolf pups are sizable, their skulls larger than those of coyotes. We discovered the signs of struggle, the telltale blood in the snow, and the pup’s remains beneath a lonely subalpine fir: a pile of coal black fur, bone shards from the legs, and the skull, skinned but completely intact. F109 and her kittens had consumed the pup completely.
Thus far, our research has supported exactly what everyone expected: Wolves dominate mountain lions in most encounters. But, this recent exchange is particularly exciting. No longer can we say that wolves dominate mountain lions in all encounters. What circumstances led to F109 turning the tables, we do not know. Perhaps F109’s predecessors served as naïve intermediaries relearning to coexist with a dominant competitor, a species absent since 1926, when the last wolf was killed in Yellowstone National Park. Perhaps F109 is evidence that lions learn quickly and adapt, and that mountain lions will successfully coexist with wolves in the Yellowstone Ecosystem for generations to come.