Mid-sized predators avoid large carnivores by hiding behind humans and dying from them
Wed, 2023-05-31 02:00
Photo courtesy of Prugh Lab, University of Washington
Sometimes the lesser of two evils is a lie, at least for mid-sized predators like coyotes and bobcats looking for safety.
When coyotes and bobcats want to avoid large carnivores, they often head for human settlements, where they die three times more often that mesopredators who stick to the wild, according to a new study published in Science. The results suggest that as wolves return to more parts of the western United States and cougar populations grow, they could end up having big effects on the ecosystem, not just where they live. , but where they do not live.
Laura Prugh, a wildlife ecologist at the University of Washington in Seattle, and her colleagues tethered deer and elk to see how their movements might change as wolves recolonize parts of Washington state. “I thought it was a great opportunity to see how large carnivores affect small carnivores,” she said. Prugh and his colleagues captured 35 coyotes and 37 bobcats in northern Washington, comparing their movements to 22 collared wolves and 60 collared cougars. They tracked the animals’ movements for five years. They also tracked if and how coyotes and bobcats died.
Wolves and cougars strongly avoided high traffic areas. When wolves and cougars were absent, so were coyotes and bobcats. But when large carnivores were present, coyotes kept well away from areas used by wolves. In Alaska, far from human presence, Prugh noted, wolves often kill coyotes. “It makes sense; wolves are definitely a real threat to them,” she said. They also avoided areas that were heavily frequented by mountain lions. perhaps because they prefer the forest, as do cougars.But in both cases, their avoidance meant that bobcats and coyotes shifted their use to more human-touched areas when wolves and cougars were present. The areas weren’t suburbs or cities. They were “ranch land, farmland, maybe a few small towns, more logging activity, just more human presence “, said Prugh. But the large carnivores always avoided it, making humans a shield for the smaller animals.
The choice had a consequence. Over the five years of the study, cougars took down two bobcats and three coyotes. The wolves killed neither. The humans, on the other hand, ended up killing 11 bobcats and 14 coyotes, most of them trapped or shot. Mesopredators were three times more likely to be killed by humans than by larger carnivores.
Geography might have impacted the study’s results, noted Christopher J. Schell, an urban ecologist at the University of California, Berkeley, who was not involved in the study. Not all human domains are created equal, he said. In this part of Washington state, “people have large tracts of land that probably have livestock,” he explained. “When they see these carnivores, they shoot them on sight.” It would be interesting, he said, to see if there are similar effects in other regions, and if people on tribal lands, for example, might be more tolerant.
Apparently not. Some of the animals were on the lands of the Spokane Indian tribe, notes Prugh collaborator Savanah Walker, a wildlife biologist for the Spokane tribe. “The mortality risk for all predators would be similar to that of surrounding rural areas,” she said.
The increase in deaths also might not impact populations of these animals, said Roland Kays, an ecologist at North Carolina State University in Raleigh, who was also not involved in the study. We know that mesopredators are moving towards humans and dying, he said, but that doesn’t mean their numbers are going down. Food opportunities provided by humans, for example, could mean that animals reproduce enough to succeed anyway.
The results show the impact of carnivores on more than their typical prey, Schell said, as they navigate living in areas cleared of humans. “The paper does a good job of centering this notion that these apex predators occupy the space they need,” he noted, which ends up leaving mesopredators “between the figurative rock and the anvil.” .
It’s possible, Prugh noted, that the effect worked in the opposite direction if coyotes turned to wolves to avoid humans. “But I think maybe they didn’t recognize humans as such a strong threat,” she said. “And so they ended up in trouble.” Coyotes and bobcats cannot smell or see the gun pointed in their direction from several hundred yards or spot the traps set. But she’s not too worried about coyotes as a species. In places where mesopredators are at exceptionally high levels due to a lack of large carnivores, “reducing their numbers may actually be a good thing.” And she knows that nothing will hold back a good mesopredator for long. Coyotes in particular “do very well in the face of human persecution and change,” she said. “They are winners.”