A wolf-colonized island gives new insights into predator and prey relationships

·6 min read

Sarah Hoy spends winter in a small cabin on a remote, snow-covered island colonized by wolves.

Drinking water comes from a hole in the ice on Lake Superior, which surrounds the island. A generator provides a few hours of electricity for laptops. A wood-burning stove provides heat.

Isle Royale is the perfect place for a researcher.

The 45-mile-long hunk of land, belonging to Michigan, offers some of the most interesting terrains for researchers examining how natural ecosystems work, and since 1958, researchers have continually monitored animal populations there.

“It’s very quiet,” said Hoy, a research assistant professor in the college of forest resources and environmental science at Michigan Technological University. “It makes it so much easier to monitor wildlife.”

Despite the serene surroundings, new research published earlier this week about wolves and moose in Isle Royale’s special environment provides fascinating insights into the relationship between predators and prey.

Wolves take down moose with arthritis and kill them at an outsized pace, according to the study in Frontiers in Ecology and Evolution. The moose on Isle Royale might need wolves, the study suggests, to keep their populations healthy from disease. The research could offer data for fresh arguments in the divisive debates over wolf management roiling many communities, where some ranchers view the creatures as a threat to their livestock and livelihoods.

A researcher's paradise

For scientists, Isle Royale has long been a fascinating fishbowl for research.

“It’s the longest-running predator-prey study in the world,” said Doug Smith, a wildlife biologist who has worked on Isle Royale in the past and now operates a wolf restoration program for the National Park Service in Yellowstone National Park.

For more than a century, scientists have observed dramatic shifts in the seesawing populations of wolves and moose.

Moose are thought to have arrived on the island first. A few animals likely swam (Moose are unsteady on ice) more than a dozen miles to the island in the early 1900s, Smith said. Their population settled into a boom-bust pattern.

“The moose eat themselves out of house and home, literally, and then they have a massive die-off. They crash, and then it starts all over again,” Smith said.

Then came the wolves.

They arrived on the island sometime around the 1940s, likely traveling over a 15-mile bridge of ice that sometimes forms between Isle Royale and mainland Minnesota.

Wolves are the only predator to eat moose on the island. “By keeping wolves in Isle Royale, you keep the moose population in check, which means they don’t eat the whole forest up,” Smith said. “Without a predator, they repeat the whole cycle.”

Diseases, tick outbreaks and severe winters have driven some population trends. But in recent years climate change made an impact so significant that the U.S. government decided to step in.

Ice bridges to the island once formed seven years out of 10. Today, these bridges form just once or twice during the same time span, Smith said.

And in recent years, the wolf population dwindled to just two — a severely inbred pair who were both father and daughter and brother and sister, according to Hoy. They couldn’t produce pups that would survive.

“It was clear why the wolf population crashed. It was because of the loss of the ice bridge. They no longer had connectivity,” Smith said. “Genetic depression.”

The moose population began to skyrocket.

The U.S. Fish and Wildlife Service began a project in the fall of 2018 to relocate wolves to the island to provide genetic diversity.

A bull moose near Pebble Creek in Yellowstone National Park in Wyoming on April 6, 2017. (Jacob W. Frank / NPS)
A bull moose near Pebble Creek in Yellowstone National Park in Wyoming on April 6, 2017. (Jacob W. Frank / NPS)

The perfect prey

Researchers visit Isle Royale at least twice each season.

“We work in the winter because it’s easier to track and observe wolves and moose. They leave tracks in the snow,” Hoy said. Aerial surveys are easier when there aren’t leaves on trees.

During summer, volunteers and researchers help collect moose remains, which provide research data points.

In the recent Frontiers study, researchers evaluated the bones of moose killed by wolves over a 32-year period from 1975 to 2007. More than 38 percent of the 1,572 moose skeletons they examined had signs of osteoarthritis.

Analysis of wolf kills suggests they preyed more frequently on old moose. Wolves didn’t appear to target moose in their prime ages, unless the moose were affected by severe arthritis, the study found.

Rates of arthritis in moose grew during years with lower kill rates from wolves, the research says.

To kill a moose, a wolf must attack an animal about 10 times its size with only its teeth, so it makes sense that wolves would succeed in taking down those unable to move well, Hoy said.

The study hints that wolves could play an important role in controlling genetic diseases by removing unhealthy animals from the population. It follows similar research in deer, which show wolves can help dampen the impacts of easily spread infections like chronic wasting disease.

“This is a good example of how the predator is actually helping the moose population,” said William Ripple, a professor and ecologist at Oregon State University, who was not involved in the research. “The wolves don’t just randomly take prey. It just so happens they will take more prey that are diseased than by chance, and that has strong evolutionary implications for natural selection.”

In other words, it’s possible that a landscape with wolves produces genetically healthier moose, though more research is needed.

Ripple said he viewed the Isle Royale research as careful and credible.

Wolf politics

Wolves are a controversial topic.

Driven to near extinction by the middle of the 20th century by poisoning, trapping and shooting, the Endangered Species Act and wolf restoration projects have pushed their numbers to more than 6,000, according to the Fish and Wildlife Service.

But wolves are not welcome in many ranching communities. The animals sometimes prey upon cattle.

When wolves came to Washington state, for example, they prompted decades of lawsuits, hard-fought political battles and even death threats — for wolves and humans alike.

In some states, poaching and poisoning cases are not uncommon, and wolves are killed by state wildlife managers after they attack livestock.

The federal protection status that has kept the species off-limits to hunting has seen dramatic changes in recent years. The Trump administration removed gray wolves from protection in most of the U.S. in 2020, allowing them to be hunted. This year, a federal judge reversed the Fish and Wildlife decision in that case, restoring protection in many areas. State policies in the northern Rocky Mountains — where wolves do not have protection — recently expanded hunting.

Despite the political battles, other research has suggested that wolves can have an outsized, positive role on ecosystems.

Years ago, Ripple revealed that aspen trees began to die off in Yellowstone following wolves’ slaughter in the 1920s. The extirpation of wolves caused a proliferation of elk, which ate baby aspen trees.

Other research suggests wolves might help keep the population of coyotes down and prevent car accidents by reducing the deer population.

Hoy hopes the new research provides a reason to avoid intensive hunting of wolves and pushes communities to consider their potential benefits.

“Think of the widespread ecological benefits wolves provide,” Hoy said. “What kind of things might we lose out on if we don’t have wolves on the landscape?”