Learning to live with large predators

Large predators around the world have long been hunted and persecuted by humans. Recently, however, many large predators are making a comeback. Mountain lions, grizzly bears, wolves, and alligators are all examples of big fierce North American predators whose populations have rebounded, thanks to conservation efforts. However, as once-rare animals become more abundant, old attitudes about the merits of killing large predators often resurface. Efforts to restore wild nature can be undermined if overreaction to the growing presence of predators leads to excessive fear-based lethal control of predators. However, as Benson et al. (1) describe in PNAS, there exists enormous variability in how human communities respond to the growing presence of predators, and the patterns can be surprising.

Benson et al. tracked nearly 600 radio-collared mountain lions (Puma concolor) in populations spanning the species’ distribution across all of California. Over more than four decades of monitoring, 263 mountain lion deaths were documented, and the cause of death was determined in nearly 200 cases. Despite a statewide ban on mountain lion hunting enacted in 1990, humans caused more than half of all mountain lion deaths in California, and lethal management ranked as the leading source of known-cause deaths. Benson et al. leveraged the extensive geographic coverage of their dataset to explore how human-caused mountain lion mortality varied across regions characterized by disparate densities of people, roads, and livestock, as well as substantial differences in public sentiment about environmental issues.

For mountain lions, one might expect human-caused mortality to increase with human population density—after all, more people means more chances for a mountain lion encounter, as well as more roads and traffic, resulting in more vehicular collisions. However, Benson et al. find that mountain lions near California’s major urban centers were relatively safe from people. It was mountain lions living in areas of intermediate human density that had the greatest risk of a human-caused death. Perhaps this pattern of risk could be due to a greater concentration of livestock in areas of intermediate human density—more interactions between predators and livestock might result in more management killings. But Benson et al. reject this hypothesis. After controlling for other factors, the density of goat and sheep farms (California mountain lions primarily target smaller livestock) was not significantly related to the risk of mountain lion mortality. A far better predictor of human-caused mortality risk to mountain lions is cultural attitudes as evidenced by voting records on environmental ballot measures. Mountain lions near human communities that were broadly supportive of environmental initiatives were less likely to die at the hands of people.

Another key finding from Benson et al. is that the deaths attributed to humans reduced the overall survival rate of mountain lions. That finding challenges a common assumption of wildlife management, which is that mortality caused by humans is compensated for by increased survival among the remaining individuals. In theory, compensation can arise if the targeted cats were likely to have otherwise died of natural causes such as disease or extreme weather or if the killing of some animals reduces competition or aggression among the remaining individuals. In practice, no such compensation was detected by Benson et al. While earlier studies (2, 3) also found no evidence of compensatory mortality in mountain lions, Benson et al. were able to clearly reject the compensation hypothesis because the spatial scale over which they collated mortality events was sufficiently large to rule out migration as a confounding factor.

As Benson et al. describe in PNAS, there exists enormous variability in how human communities respond to the growing presence of predators, and the patterns can be surprising.

The lack of compensatory mortality is important. The implication is that lethal management is not without consequences for population dynamics, and this in turn reinforces the need to identify alternative, nonlethal management strategies so as to not undo recent conservation gains. Yet, managers commonly turn to lethal tactics. Over the last two decades, the US Department of Agriculture’s Wildlife Services killed hundreds of mountain lions each year across the United States (Fig. 1). These kills were in addition to those sanctioned by state wildlife agencies for hunting and/or management. For example, the California Department of Fish and Wildlife reported a minimum of 1,834 mountain lions killed under state-issued depredation permits issued from 2001 to 2020 (4).

Fig. 1.

From 2000 to 2021, Wildlife Services killed, on average, 340 mountain lions each year in the United States (5). These kills were in addition to those permitted by various state wildlife agencies.

Benson et al. point out that livestock losses are the primary catalyst for lethal management of mountain lions. It remains an open question whether, or how frequently, mountain lions might be wrongly blamed for losses that are due to other causes or other predator species. Such misappropriation of blame is known to occur in the case of wolves, for example (6).

Regardless, lethal management and hunting of predators should be measures of last resort given the important role that predators play in shaping ecosystems (7), as well as the fact that many people cherish the presence of dangerous wild animals in our otherwise tame world. For example, many Southern Californians mourned the death of P-22, the mountain lion that was often seen near Los Angeles’ famous Hollywood sign (8). Given the functional and intrinsic value of large predators, studies aimed at improving the effectiveness of nonlethal management should be a top priority (9, 10). Nonlethal methods are especially important because killing predators can be costly and ineffective (9, 10) and, worse, can have the opposite effect of what is intended, as has been observed in wolves. Specifically, lethal management of predators can increase, rather than reduce, predation on livestock (11). Fencing combined with guard animals and other deterrents can be effective at protecting livestock, and there is some evidence that keeping existing predators in their territories may reduce human–wildlife conflict.

Learning to coexist with rebounding populations of large predators is a major challenge for conservation and for society as a whole. The study by Benson et al. is exemplary in its geographic breadth and the large number of mountain lions studied. Their exploration of how mountain lion mortality varies across regions shines light on the role that human attitudes can play in decisions about using lethal management. Future comparisons across states that contrast sharply with California in terms of regulations and public attitudes would further advance our understanding of the interplay between human values and the management of large carnivores such as mountain lions. Making such comparisons is a serious challenge, however, because each state’s wildlife agency collects data in its own idiosyncratic way, and data are often buried in reports (6). Understanding the population consequences and cost-effectiveness of different strategies for managing wide-ranging predators will require interagency coordination and transparent sharing of data. However, in the end, cultural perceptions and attitudes will determine how well people can live with large predators.