Editor's Note: A version of this post is published on National Geographic's Cat Watch blog. Read that post here.
I found the fresh footprints of a subadult male puma not one mile from the typically bustling headquarters of the High Lonesome Ranch in western Colorado, USA. But it was early and the ranch had yet to wake. I sat on the track in the pitch black, awaiting sunrise and the arrival of our houndsmen, Grant and Cody. My radio crackled soon enough, and I told them where I was. Not long after they arrived, we caught a young male we called P3. He weighed 46 kg (102 lbs), and was approximately 18-20 months of age. He hadn’t left his mother all that long ago.
P3 remained in our study area only a day; he was likely dispersing in search of his own territory when we caught him. He moved east, and north, paralleling Interstate 70. We followed, conducting field investigations in search of prey remains in every location where he spent four or more hours. While he traveled, just 8% of his diet was adult elk or deer, which made sense given that large, adult ungulates could be dangerous. Pumas are occasionally killed when pierced or crushed by antlers or horns, or when thrown by large prey and subsequently slammed into trees. Instead of deer and elk, an amazing 28% of P3’s diet was North American porcupines. Porcupines differ from other mammals in North and South America, in that they wear weapons to deter potential predators. Porcupines are covered by approximately 30,000 quills—sharp, rigid, hollow hairs 2-10 cm long, and each tipped with 700-800 barbs.
In contrast, when P3 established a home range four months later and 65 miles northeast of where we captured him, 32% of his diet was adult deer and elk, and his intake of porcupines dropped to just 12%. In fact, after several months in his new territory, he stopped eating porcupines all together. P3’s pattern of foraging was repeated several times as we followed dispersing pumas in the Rocky Mountains and thus, a question was born. Could we predict when and why pumas choose dangerous prey?
Ecologists have in fact already made predictions about such things. Large carnivores should kill prey larger than themselves—because then they save energy by hunting less often. Nevertheless, Hayward et al. (2007) found that young African lions hunted small prey while they learned the requisite skills to take down larger, more dangerous prey. Following this research, Jen Feltner, Howard Quigley and I formed our first prediction: young pumas would avoid adult deer and elk, because of the dangers they posed to inexperienced hunters.
Somewhat in contrast to what was documented in African lions, ecologists also predict that juvenile predators, individuals of lower social rank, and hungry, less-experienced individuals are more likely to take additional risks and engage dangerous prey (Mukherjee & Heithaus, 2013). Thus, our second prediction was that young, inexperienced, dispersing pumas unfamiliar with the terrain through which they passed would be more likely to engage porcupines, a small, easy to handle prey, but one made dangerous by the quills they wear.
When we stepped back to assess a sample of pumas, the pattern was very clear—each of the ecologists before us was right. Though young, dispersing pumas avoided dangerous adult elk and deer and disproportionately hunted smaller game, they also disproportionately killed small but dangerous porcupines. We believe this stage-dependent foraging pattern (young, dispersing animals versus resident adult pumas) is important in describing the ecology of pumas, as well as in identifying potential dispersal habitat that could see puma expansion in areas of North and South America where they were previously eradicated.