The resurgence of apex predators and wolf populations across the continental United States, a result of measures under the Endangered Species Act, has been a hot topic among conservationists. While wolves, along with other apex predators, have been recognized for their role in keeping smaller predator species in check, new research now reveals an unexpected facet of this ecological dance.
The study, published in the journal Science on May 18, reveals that in Washington state, the dual presence of apex predators – wolves and cougars – does regulate populations of mesopredators, such as bobcats and coyotes.
However, the twist in the tale lies in the fact that these apex predators were not found to be the primary cause of mortality among the mesopredators.
Instead of falling prey to the fangs and claws of their larger counterparts, the bobcats and coyotes were driven into areas with higher human activity. The consequences were inevitable – it was the humans who ended up playing the grim reaper.
The study was led by wildlife ecologist Laura Prugh and her collaborative team from the University of Washington, the Washington Department of Fish and Wildlife, and the Spokane Tribe of Indians.
The experts discovered that bobcats and coyotes were more than three times as likely to die from human activities, such as hunting or trapping, than from encounters with cougars and wolves.
This revelation provides a stark illustration of how humanity’s ever-expanding footprint is significantly altering interactions among wildlife 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,” explained Professor Prugh.
“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 investigation, the researchers embarked on a five-year journey, from winter 2017 to summer 2022, tracking the activity of 22 wolves, 60 cougars, 35 coyotes, and 37 bobcats in two study areas in north-central and northeastern Washington as part of the Washington Predator-Prey Project.
They used GPS collars to monitor the animals across a diverse landscape comprising national forests, camping, hunting, and fishing recreational areas, as well as lands devoted to agriculture, timber harvesting, ranching, and residential use.
The study revealed a fascinating shift in animal behavior. When wolves or cougars moved into their region, bobcats and coyotes altered their movements to avoid them.
“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.
Further, upon investigating the causes of death for any animals tracked during the study, the team found that areas with high human activity were far more lethal for mesopredators than those with a lesser human presence.
For instance, of the 24 coyotes that died during the study, over half were killed by humans. Similarly, humans were responsible for half of the 22 bobcat deaths recorded. Some mesopredators were shot after preying on livestock, others were targeted for threatening poultry.
In a nutshell, human activities accounted for three to four times more mesopredator deaths in this study than the apex predators – wolves and cougars.
Interestingly, the study doesn’t signal immediate danger for the overall populations of bobcats and coyotes, which rank among the most widespread mesopredators in North America. Neither are endangered, and coyotes especially are highly adaptable to human presence.
However, Professor Prugh warns that not all mesopredator species share this resilience. Some reproduce more slowly, while others may be vulnerable in multiple ways to human activities. For example, rodent poisons used in pest control can be lethal for fishers, another type of mesopredator.
Looking forward, researchers need to investigate how mesopredators use space and resources in areas with high human activity. They should also explore the potential risks these shifts pose to humans. “These are not trivial shifts in territory or space. There are real consequences,” said Professor Prugh.
The study also sheds new light on the “human shield hypothesis,” a working theory in wildlife-human interactions. This hypothesis suggests that prey species move to areas with higher human activity due to the presence of predators.
Instances of this behavior can be seen in Yellowstone National Park, where elk have moved near hiking trails, typically avoided by wolves and other large carnivores.
However, the human impact in areas like Yellowstone is typically less compared to other recreational spaces or farming, grazing, and residential developments. This has prompted scientists to question the efficacy of humans as a “shield” in such environments.
“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,” Prugh said.
“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.”
The research presents a sobering reminder of our role in reshaping wildlife interactions. As apex predators continue to reclaim their former habitats, our growing human footprint also modifies these ecosystems.
Balancing our presence with the needs of these animals becomes an ever more pressing issue. The dance between apex predators, mesopredators, and humans continues to play out, and only time will tell where this dynamic interaction will lead us.
The research was funded by the National Science Foundation, the Washington Department of Fish and Wildlife and the Australia Fulbright Program.
A “mesopredator” is a term used in the science of ecology to identify medium-sized, mid-ranking predators that are not apex predators. This category includes a broad variety of species across numerous animal groups, which can vary according to the specific ecosystem and food web under consideration.
Generally speaking, mesopredators are small to medium-sized carnivores that occupy an intermediate trophic level in food webs. Examples of mesopredators include raccoons, skunks, foxes, and coyotes in North America, or jackals and servals in Africa. In aquatic environments, mesopredators might include certain species of sharks or large fish.
One crucial role of mesopredators in an ecosystem is controlling the populations of smaller animals, usually herbivores or omnivores, which they prey upon. This relationship can help maintain a balance and biodiversity in the ecosystem.
However, the population and behavior of mesopredators are often controlled by larger predators, or apex predators. In ecosystems where apex predators have been removed or their populations significantly reduced (often due to human activity), mesopredators can become overabundant.
This situation, referred to as “mesopredator release,” can lead to declines in the prey species and overall biodiversity loss. For example, in the absence of wolves (an apex predator), coyote (a mesopredator) populations can increase, leading to declines in smaller mammal and bird populations.
Furthermore, as demonstrated in the study discussed earlier, mesopredators can have complex relationships with humans.
Some mesopredators have adapted well to human-dominated environments and can live in close proximity to human settlements (e.g., urban foxes or coyotes). However, this proximity can also make them more susceptible to threats such as vehicle collisions, hunting, trapping, or poisoning.
In terms of reproduction and survival rates, mesopredators can vary widely. Some species, like coyotes, can quickly adapt to a variety of environments and have relatively high reproduction rates, enabling their populations to sustain despite threats. In contrast, other mesopredators may reproduce more slowly or be more vulnerable to human activities, potentially leading to population declines in certain areas.
Overall, mesopredators play a vital role in maintaining the health and balance of ecosystems. Understanding their behavior, interactions with other species, and responses to human activity is essential for effective wildlife management and conservation strategies.