This blog post is provided by Kristin Barker and tells the #StoryBehindthePaper for the paper “Large carnivores avoid humans while prioritizing prey acquisition in anthropogenic areas“, which was recently published in Journal of Animal Ecology. In the study, they investigate the impact of human activity on the behaviour of grey wolves, finding a nuanced response to different human influences depending on the context.
Right now, populations of large carnivores like grizzly bears and grey wolves are recovering across the globe. There’s a common story in ecology that these predators deliberately avoid humans, and many of our key ecological theories hinge on this story. For example, we attribute the increasing use of human areas by ungulates (hooved mammals) to the reduced predation risk afforded by large carnivores’ avoidance of humans. But livestock producers and others who live in carnivore recovery areas share stories of large predators killing and eating prey right in front of humans with no apparent avoidance response.
To reconcile the disparity between our expectation that large carnivores should avoid humans and the reality that sometimes they don’t, we need to understand how these animals perceive and respond to humans. Are large carnivores scared of humans only if we directly threaten them, for instance by hunting? Or are they not scared at all, but rather just generally disturbed by human activity, in which case we would expect a weaker but more generalized avoidance of humans? It’s also possible that carnivores are attracted to human areas where ungulate prey concentrate in predictable places and times, but it’s not clear whether this potential food benefit might outweigh the costs of potentially interacting with humans. Teasing apart carnivore perception of humans could help resolve some of the uncertainty around carnivore responses to humans in different contexts.
To answer these questions, and to investigate whether human-induced behavioral changes in large carnivores affect the risk of predation for their ungulate prey, we launched a new field campaign in the southeastern Greater Yellowstone Ecosystem, USA. Over the course of three winters we skied, snowshoed, waded, and snowmobiled to more than 1000 potential wolf kill sites. We then contrasted characteristics of the 170 wolf kills we found with those of matched non-kill sites to quantify how predation risk changed as a function of human influences, while controlling for key environmental factors. Specifically, we evaluated the effects of roads, trails, and human-run ungulate feedgrounds, and we also investigated whether wolves responded more strongly to these influences if they had previously been hunted by humans and/or if it was during the day when humans were most active.
We found that wolves did change their predatory behavior in response to humans, but they didn’t unequivocally perceive humans as either scary, disturbing, or beneficial. Instead, wolves in our study area actively distinguished between different types of human influences based on the immediate costs and benefits of each. For example, we found opposite responses of wolves to roads and trails. Wolves preferentially made kills far from paved, plowed roads but close to unplowed oversnow trails, despite plowed roads making it much easier to travel through the snowy landscape. However, wolf response to human influences was much weaker – and in some cases nonexistent – in areas where prey availability was particularly low. Furthermore, despite their preference for using unplowed trails to access their prey, wolves avoided killing prey near trails during the day when humans were most likely to be using them.
This nuanced response of wolves to different human influences helps clear up superficially incongruous results from other studies and personal observations. Based on our finding that wolves actively differentiate between the immediate risks and rewards of multiple simultaneous human influences, it is not surprising that wolves respond very differently to humans in different contexts. Our work suggests that the degree to which wolves alter their predatory behavior hinges on the availability of ungulate prey in conjunction with the intensity or predictability of human use. In particular, in areas where prey are scarce, wolves may be unlikely to prioritize avoiding humans over acquiring prey despite their general avoidance of human activity. In the next phase of our research, we are building on these findings to investigate how the responses of wolves to humans can directly and indirectly affect populations of their native prey.
As populations of large carnivores continue to recover across the globe, they will inevitably continue to expand into human-dominated areas. Wildlife managers, conservationists, policymakers, and local stakeholders all have a vested interest in anticipating and responding to the ecological and socioeconomic effects of carnivore recovery. By unveiling some of the nuance behind wolf response to humans, we hope our work can help inform strategies to mitigate concerns related to human-wildlife conflict, prey population dynamics, and undesirable ungulate distributions in human-dominated areas.
Read the paper
Read the full paper here: Barker, K J., Cole, E., Courtemanch, A., Dewey, S., Gustine, D., Mills, K., Stephenson, J., Wise, B., & Middleton, A D. (2023). Large carnivores avoid humans while prioritizing prey acquisition in anthropogenic areas. Journal of Animal Ecology, 00, 1– 12. https://doi.org/10.1111/1365-2656.13900