When wolves move in, they push smaller carnivores closer to human development – with deadly consequences

When wolves move in, they push smaller carnivores closer to human development – with deadly consequences

(The Conversation is an independent and nonprofit source of news, analysis and commentary from academic experts.)

(THE CONVERSATION) Large carnivores like wolves are returning to areas they used to occupy, leading scientists to wonder whether they may once again fulfill important ecological roles. But wolves’ return to the landscape can affect other nearby animals in complex ways.

Our research, published in the journal Science, shows that an increase in predators can lead smaller carnivores, like coyotes and bobcats, to seek refuge near people – but humans then kill them at even higher rates than large predators do.

We are wildlife ecologistswho study how predators shape ecosystems. Along with colleagues from the Washington Predator Prey Project and the Spokane Tribe of Indians, we are seeking to understand how recoveries of wolves and other predators are altering ecosystems in Washington state.

Predators structure ecosystems

Large carnivores play crucial roles in their ecosystems. As they prey on or push other animals to avoid the areas they frequently use, predators shape the way interconnected food webs work.

The iconic reintroduction of wolves to Yellowstone National Park in 1995 had cascading effects down the food chain. The elk population shrank, and those that remained avoided areas with wolves, termed a “landscape of fear.” These changes in elk abundance and behavior allowed aspen and willow trees to recover after decades of overconsumption by elk.

Wolves also kill smaller predators like coyotes, providing respite for the animals that coyotes eat. Research from Yellowstone suggests that landscapes with wolves may have more diverse vegetation and more small animals like songbirds than those without wolves.

But because humans are often intolerant of predators and kill them at high rates, large predators tend to avoid areas that are frequented by people. In national parks where humans rarely kill wildlife, some prey species use areas popular with people, such as hiking trails and campgrounds, as refuges from predators. This is known as the “human shield” effect.

Predators in human-dominated landscapes

Three decades after the Yellowstone release, wolves have continued to recolonize vast areas of the American West. In 2008, after an 80-year absence, wolves – some of which descended from the original Yellowstone population – began to naturally recolonize Washington. These wolves moved in from neighboring populations in Idaho and British Columbia.

But unlike Yellowstone, many of the landscapes wolves are now returning to are heavily modified by humans. This level of development raises the question: Do predators have the same influence on ecosystems where humans, rather than wolves, are the top dogs?

To answer this question, we used GPS collars to track the movements of 22 wolves, 60 cougars, 35 coyotes and 37 bobcats as they navigated the landscapes of northern Washington, comprising a patchwork of public forests and land used for agriculture, ranching, logging and residential development.

Using hundreds of thousands of GPS locations, we constructed statistical models to reveal how coyotes and bobcats navigated a landscape where humans, wolves and cougars all posed concurrent threats. The GPS collars also notified us when coyotes and bobcats died, allowing us to investigate what caused their deaths.

When ‘human shields’ are lethal

We found that wolves and cougars avoided areas heavily influenced by humans, such as busy roads and residential areas. Coyotes strongly avoided wolves, which brought them closer to humans. In parts of the landscape with large predators around, both coyotes and bobcats moved to areas with approximately double the human influence, potentially using humans as shields.

When coyotes and bobcats sought refuge near people, they instead encountered a more lethal source of danger. We found that humans were the greatest cause of mortality, killing these smaller predators at more than three times the rate that large carnivores did.

Our findings fit with earlier research that characterizes humans as “super predators.” People use modern technologies such as firearms and steel traps to kill small predators at far higher rates than other predators kill small predators. Unlike other predators, humans often target animals in prime condition.


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