Small Predators Seek Safer Areas Despite Greater Risk from Large Predators

Medium-sized carnivorous species – mesopredators like coyotes or bobcats – tend to move into human-dominated areas to avoid predation by larger carnivores, a phenomenon also known as the "human shield" effect. However, according to a new study, doing so places these safety-seeking species at considerably greater risk for mortality due to human activities. The findings describe a "paradox of the lethal human shield" for mesopredators, which could become an increasingly important driver of carnivore community dynamics and ecological trophic structures as species restoration and recovery efforts expand the coexistence of large predators and humans in shared landscapes. Although the use of human shields has been linked to increased wildlife survival rates in some instances, it also has the potential to impose increased risk for human-caused mortality through hunting, human-wildlife conflict removals, or vehicular collisions. However, the interacting dangers posed by large carnivores and humans affect the behavior and mortality of smaller predators remains poorly understood. Using data from radio-collared coyotes and bobcats (mesopredators), as well as wolves and cougars (sympatric large carnivores), Laura Prugh and colleagues investigated the movements of these animals in relation to one another and in relation to substantial human activities across northern Washington state. Prugh et al. found that smaller predators tended to move away from the larger predators into areas with greater human influence, suggesting the smaller species perceived humans to be less of a threat than larger carnivores. However, rather than shielding mesopredators and improving their overall survival, the authors discovered that the human-caused mortality rates for mesopredators were more than three times higher than large-carnivore-caused mortality in these areas. Prugh et al. suggest that this scenario could represent an ecological trap. "Despite uncertainty among underlying behavioral and evolutionary processes, the study by Prugh et al. highlights the ecological implications of human influence on relationships among multiple trophic levels," write Chris Darimont and Ishana Shukla in a related Perspective.