Out of the frying pan: Coyotes, bobcats move into human-inhabited areas to avoid apex predators — only to be killed by people
IMAGE: THIS IMAGE SHOWS A BOBCAT BEING RELEASED BACK INTO THE WILD IN FEBRUARY 2020 AFTER BEING FITTED WITH A GPS COLLAR AS PART OF THE WASHINGTON PREDATOR-PREY PROJECT. view more
CREDIT: ZACHARY WARDLE
Link to Google Drive folder containing images:
https://drive.google.com/drive/folders/1Wv5Va5E0Pti0kLRogMUdoSnCEIaWlEFy?usp=sharing
Since their protection under the Endangered Species Act, wolf populations have been making a comeback in the continental United States. Conservationists have argued that the presence of wolves and other apex predators, so named because they have no known predators aside from people, can help keep smaller predator species in check.
New research shows that in Washington state, the presence of two apex predators — wolves and cougars — does indeed help keep populations of two smaller predators in check. But by and large the apex predators were not killing and eating the smaller predators, known as mesopredators. Instead, they drove the two mesopredator species — bobcats and coyotes — into areas with higher levels of human activity. And people were finishing the job.
The study — published May 18 in the journal Science by researchers at the University of Washington, the Washington Department of Fish and Wildlife and the Spokane Tribe of Indians — reports that bobcats and coyotes were more than three times likely to die from human activity, like hunting or trapping, than from the claws and jaws of cougars and wolves.
The findings illustrate how humankind’s growing footprint is changing interactions among other species.
“When cougars and wolves moved into an area, coyotes and bobcats employed a specific strategy to avoid apex predators by moving into more human-impacted regions,” said lead author Laura Prugh, a wildlife ecologist and UW associate professor in the School of Environmental & Forest Sciences. “That indicated to us that coyotes and bobcats likely perceived these large carnivores as a greater threat to them than people. But when we looked at causes of mortality for the mesopredators, humans were by far the largest cause of death.”
For the study, researchers used GPS collars to track the activity of 22 wolves (Canis lupus), 60 cougars (Puma concolor), 35 coyotes (Canis latrans) and 37 bobcats (Lynx rufus) across two study areas in north central and northeastern Washington from winter 2017 to summer 2022 as part of the Washington Predator-Prey Project. The study areas — which included portions of Okanagan, Stevens, Spokane, Pend Oreille and Lincoln counties — consisted of national forests; recreational areas for camping, hunting and fishing; and lands dedicated to agriculture, timber harvesting, ranching and residential use.
Tracking data indicated that, when wolves or cougars moved into their region, bobcats and coyotes would shift their movements accordingly.
“Coyotes and bobcats started using areas that had twice as much human influence compared to where they were before the large carnivores moved in,” said Prugh.
Researchers also attempted to determine the cause of death for any tracked animals that died during the study period. They discovered that areas with high human activity were far more deadly to mesopredators than those without a large human presence.
More than half of the 24 coyotes that died over the course of the study were killed by people. Some were shot after preying on livestock. Humans also killed half of the 22 bobcats that died during the study, including several that were attacking chickens.
In general, humans killed between three and four times more mesopredators in this study than wolves or cougars, both of which typically avoid areas with high levels of human activity.
In the short term, human activity poses little threat to the overall populations of bobcats and coyotes, which are two of the most widespread mesopredators in North America. Neither are endangered, and coyotes in particular are highly adaptable to the presence of people.
But not all mesopredator species are as resilient in human areas as coyotes and bobcats, said Prugh. Others reproduce more slowly or may be vulnerable in multiple ways to human activity. Rodent poisons used to keep away pests, for example, can kill fishers, another mesopredator species.
Future studies would need to investigate how mesopredators use space and resources in areas with high human activity, and what the risks of these shifts are to people.
“These are not trivial shifts in territory or space,” said Prugh. “There are real consequences.”
The findings also add a wrinkle to a working theory of wildlife-human interactions called the human shield hypothesis. Under the hypothesis, the presence of predators in a region causes prey species to move to areas with higher human activity. In Yellowstone National Park, for example, elk have at times moved near hiking trails, which wolves and other large carnivores typically avoid.
But the impact of humans in Yellowstone is typically smaller compared to other types of recreational areas or farms, grazing lands and residential developments – leaving some scientists to wonder if humans would be much of a “shield” in those areas.
“In these areas with higher levels of human activity, it was unknown whether a mesopredator would perceive the apex predator or humans as the greater threat,” said Prugh. “Here, we found that bobcats and coyotes perceived their apex predators as the greater threat, but their strategy of avoiding those large carnivores backfired by bringing them into contact with a much more effective predator: us.”
Co-authors are UW postdoctoral researcher Calum Cunningham; former UW researcher Rebecca Windell; Brian Kertson, a biologist with the Washington Department of Fish and Wildlife; Taylor Ganz, a UW doctoral student in environmental and forest sciences; Savanah Walker with the Spokane Tribe of Indians; and Aaron Wirsing, UW professor of environmental and forest sciences. The research was funded by the National Science Foundation, the Washington Department of Fish and Wildlife and the Australia Fulbright Program.
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For more information, contact Prugh at lprugh@uw.edu.
Grant numbers: DEB-1652420, 16-07846
Reference: Prugh LR, Cunningham CX, Windell RM, Kertson BN, Ganz TR, Walker SL and Wirsing AJ. “Fear of large carnivores amplifies human-caused mortality for mesopredators.” Science 2023. DOI: 10.1126/science.adf2472
A note from Science for journalists: “Advance copies of embargoed papers may be obtained by registered reporters from our press package, SciPak, at https://www.eurekalert.org/press/scipak/. For reporters having difficulties accessing the paper from the press package, please have them contact scipak@aaas.org. After embargo lift, anyone may view a copy of your manuscript at https://www.science.org/journal/science.”
This video shows UW researchers trapping a bobcat in 2020, fitting it with a GPS collar and releasing it as part of the Washington Predator-Prey Project:
https://www.youtube.com/watch?v=fYPCD6yKNHs [Credit: Calum Cunningham]
JOURNAL
Science
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
Animals
ARTICLE TITLE
Fear of large carnivores amplifies human-caused mortality for mesopredators
ARTICLE PUBLICATION DATE
18-May-2023
This image taken by a game camera at night shows a coyote wearing a GPS collar in September 2018 as part of the Washington Predator-Prey Project.
CREDIT
Savanah Walker
Fear of large predators drives smaller predators into areas they perceive as safer, but where risk is greater
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.
JOURNAL
Science
ARTICLE TITLE
Fear of large carnivores amplifies human-caused mortality for mesopredators
ARTICLE PUBLICATION DATE
19-May-2023
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