Wolves Are Thriving at Michigan’s Isle Royale National Park, Reaching Their Highest Numbers in Almost 50 Years, New Data Suggests
Scientists estimate that 37 of the animals are now roaming the rugged archipelago, which has contributed to the dwindling moose population. But the predators and prey might be nearing a tipping point
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The gray wolf population on a rugged archipelago in northwestern Lake Superior has surged to its highest number in nearly 50 years.
After completing their annual survey earlier this year, scientists estimate 37 of the apex predators are now roaming around Isle Royale, a 132,000-acre U.S. national park that’s part of Michigan and located near Thunder Bay, Canada. The moose population, meanwhile, has declined to an estimated 524 animals, according to a report released in April.
Together, the new figures suggest Isle Royale is returning to a healthier predator-prey dynamic after years of imbalance.
“The wolf and moose populations are now approaching the edge of where they have been in the past, with moose low and wolves high,” says Rolf Peterson, an ecologist at Michigan Technological University and co-leader of the Isle Royale Wolf-Moose Project, in a statement.
Did you know? Visiting Isle Royale
Isle Royale National Park is open to visitors from mid-April through the end of October. But it’s usually one of the least-visited national parks in America, largely due to its remoteness. The only way to reach the main island is by ferry, seaplane or private watercraft.
Scientists have been studying the complicated relationship between wolves and moose on the remote island chain since 1958. The study, now in its 68th year, is the world’s longest continuous predator-prey study.
Researchers believe moose first arrived on Isle Royale in the early 1900s. For decades, they lived on the archipelago without any natural predators. Then, in 1948, the animals’ lives changed forever: Wolves showed up, likely by crossing an ice bridge from Canada.
The populations of the two creatures have varied greatly depending on weather conditions, food availability, disease and other factors. Still, wolves are the sole predator of the moose—and beavers—that live there. Since 1980, the moose population has been as low as 500 animals and as high as 2,400. During that same time frame, wolves have gone from a high of 50 animals to just two highly inbred individuals.
In 2018 and 2019, the National Park Service (NPS) trapped wolves in Minnesota, Canada and Michigan’s Upper Peninsula and translocated them to the island. They hoped the 19 newcomers might help improve genetic diversity and boost the predators’ numbers, leading to a more balanced dynamic between wolves and moose.
So far, that initiative appears to be achieving its desired outcomes. Since 2019, researchers have observed numerous litters of wolf pups on the island—and the moose population has been dwindling.
Wolves are predating on the lumbering ungulates, but they’re also contributing to their own demise by overbrowsing young balsam fir trees, which prevents the plants from maturing and dropping fir cones that would lead to the growth of more firs. In recent years, the trees have also been infested with spruce budworms, moth larvae that feast on needles and buds.
This year, scientists conducted their annual survey from January 22 through March 3, making observations from planes, following tracks on the ground and inspecting kill sites.
Based on the data, Peterson and his colleagues suspect wolves killed 24 percent of the island’s moose population over the last year. But the researchers also observed record-low growth rates for balsam fir, a primary source of food for the island’s moose, especially in the winter. Isle Royale’s young balsam fir trees grew a little more than an inch, on average, over the last year. For comparison, the trees grow an average of nearly eight inches taller during years when moose don’t put as much pressure on them.
Though moose numbers are now declining, the animals heavily browsed the island’s balsam fir saplings from 2018 to 2021. This year’s findings suggest the trees still haven’t rebounded from that period.
“They’ve been hammered by moose, particularly in the early years of their growth, and so they’re just barely able to hang on, and they really haven’t recovered their growth yet,” Peterson tells the Daily Mining Gazette’s Graham Jaehnig.
The 37 wolves are split into three packs, the West Pack, East Pack and Northeast Pack, which are all expected to welcome pups this spring. Meanwhile, for the first time since the study began, scientists did not observe a single moose calf this winter. That wasn’t a surprise, given the high level of wolf predation on the ungulates.
Zooming out, the ecosystem appears to be reaching a tipping point. Though the wolf population is increasing and moose numbers are decreasing, researchers expect those trends to stabilize in the near future.
“There is going to be a point in which the wolf population starts to decline,” Sarah Hoy, an ecologist at Michigan Tech who co-leads the Isle Royale Wolf-Moose Project, tells WLUC’s Colin Jackson. “When food is low, the number of wolves is going to start to go down. We’re very close to a turning point.”
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