The Wolves and Moose of Michigan’s Isle Royale Battle for Survival


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In the northwest corner of Lake Superior’s icy waters, the ancient drama of life and death, predator vs. prey, plays out on Michigan’s Isle Royale. Observation of this struggle, now in its 64th year, is the world’s longest predator-prey study.

The National Park Service is in the thick of collecting data for the 2023 Isle Royale Wolf Report. Winter, with its absence of leaves and white ground, is the ideal time for aerial surveys. The results should be available this spring.

The winter study is a collaboration between the NPS, Michigan Tech, and the ongoing research project, Wolves and Moose of Isle Royale.

Estimates from the 2022 report (based on a 38-day study) include:

  • 28 wolves
  • 1,346 moose
  • 4% moose population growth rate
  • 8.9 moose killed annually per wolf
  • 26 inches average snow depth
  • 12.2 degrees Fahrenheit

The study also estimates a whopping 457 beaver colonies (lodges, dams). Colonies average five beavers. Beaver is a preferred food of the wolves when they can get it.

Wolves are the apex predators in Michigan’s Isle Royale National Park, the subject of the world’s longest-running predator-prey study. Photo credit: NPS/Courtesy of J. Vucetich, Michigan Technological University

Moose arrived on Isle Royale in the early 1900s, crossing an ice bridge from Canada. Isle Royale became a national park in 1940. Then, the wolves came in the late 1940s, and everything changed. Catching wind of something unique, the scientists showed up in 1958 to begin their landmark research.

Wolves and Moose of Isle Royale, states on its website, “The project began during the darkest hours for wolves in North America—humans had driven wolves to extinction in large portions of their former range. The hope had been that knowledge about wolves would replace hateful myths and form the basis for a wiser relationship with wolves.”

After several years of predator-prey research on Isle Royale, ecologists noted not much had changed between the wolves and moose. The conclusion was that the ecosystem had achieved a “balance of nature,” a commonly accepted norm for the dynamics of the natural world. But scientists kept observing and their patience paid off in a big way.

Isle Royale is 45 miles long, and its widest point is nine miles. Its modern-day name comes from French Jesuit missionaries honoring their royal patrons. Photo credit: NPS

Eleven years later, the moose population had doubled. This startling shift in the balance of nature procured more funding for further research. By 1980, the moose population had tripled from its original size and then declined to half its maximum size. During that save time, wolves more than doubled to fifty. The study was proving that rich, dynamic variation, not “balance of nature” was the force that guides nature.

The wolf population then suffered further fluctuation, dropping from 50 to 14 due to a canine virus. The population partially recovered during the 1980s, only to fall again in the next decade. Researchers were perplexed. Disease was gone. Food was abundant. What they discovered was Isle Royale’s isolation, so advantageous for research, created a natural barrier for wolf health. All of Isle Royale’s wolves were highly inbred, descending from a single female and two males.

The moose also experienced dramatic change. With low predation in the late 1980s and early 1990s, their population tripled to almost 2,400. But in 1996, a lack of food, an abundance of moose ticks, and a severe winter decimated moose numbers from their all-time high to just 500.

Pictured here is the first wolf released on Isle Royale, one of four transported in from Minnesota. Photo credit: NPS / Jacob Frank

Salvation temporarily came in the winter of 1997 when a wolf crossed the ice bridge bringing new life for the wolves. By 2006, Isle Royale had 30 wolves in three packs. The recovering moose population dropped again due to weather effects and tick-borne disease to an all-time low of just 385 animals. The moose recovered from there and grew to 1,250 by 2015.

The wolf population, however, declined to just three by 2015. The National Park Service (NPS) began determining what, if anything, to do. The idea of relocating wolves to the island went against the NPS’s policy of “Let nature take its course.” The NPS surmised by following its hands-off policy. Extirpation was imminent. The moose would then flourish and overpopulate the island decimating their food source, resulting in mass starvation. Wanting to avoid this, along with tremendous public outcry for wolf relocation, prompted the NPS’s decision in the spring of 2018 to relocate 20-30 wolves to Isle Royale over the following three years.

That fall, with only two wolves remaining on the island, the NPS relocated four wolves from Minnesota. Over the next twelve months, 19 wolves from Minnesota, Michigan, and Ontario would be given a new home on Isle Royale. The Michigan wolves were captured from Baraga, Gogebic, Houghton, and Ontonagon Counties in the Upper Peninsula.

Of those 19, one returned over the ice bridge to the area from where it came. Four wolves were killed by other wolves. This type of conflict is common as wolves defend and establish territories and pack hierarchy. Two wolves died of illness. Two others died from unknown causes.

From left, National Park Service veterinarian Michelle Verant, Michigan Department of Natural Resources veterinary specialist Dan O’Brien and Michigan DNR wildlife technician Brad Johnson take vital signs and measurements of a gray wolf captured Sept. 6, 2019, in Michigan’s Upper Peninsula. Photo credit: NPS / John Pepin

But the good news is the wolves are thriving. NPS trail cameras recorded two wolf pups in 2019. Scat samples taken in September 2020 suggested two different litters of pups at the east end of the island. Michigan Tech cameras recorded footage of four wolf pups in January 2021. Wolf and moose surveys have been interrupted by the pandemic, and current counts are not known.

Whereas the wolves are doing well, the moose seem to be in decline again. “Moose really struggled to find enough food this past winter,” says Sarah Hoy, MTU research assistant in a July 12 article. “Because there have been such large numbers of moose on the island over the last five years and moose ate branches faster than the trees can recover and replace them, the amount of food available to moose during winter has been getting progressively worse each year since 2017.”

The ongoing predator-prey study on Isle Royale has taught the scientific community that nature is unpredictable. At best it can be influenced but never controlled.


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