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New research confirms old theory: Wolves really do prefer old and sick moose

Michigan Tech scientists found Isle Royale wolves show a definite preference for old moose and those with osteoarthritis.

wolves chasing moose on Isle Royale
A pack of Isle Royale wolves chasing a moose later found to be suffering from osteoarthritis. New research shows wolves on the island do indeed select older moose and those with disease more often as their prey.
Contributed / Rolf Peterson, Michigan Tech
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ISLE ROYALE, Mich. — It’s long been assumed that wolves will prey upon the easiest meals out there, including the sick, the very young and the old among the deer or moose they live with.

Now, a new study by Isle Royale researchers from Michigan Technological University has documented that assumption as fact, and found that wolves play a key role in keeping moose populations healthy on the big Lake Superior island.

Wolves on the island showed a strong preference for elderly moose over prime-age moose, with wolves selecting their targets based on the age of the moose and whether it suffered from osteoarthritis, a chronic disease that can be influenced by genetics and injuries.

“The results indicate that wolves play an important role in keeping prey populations healthy and have considerable implications for the conservation management of predator and prey populations,” the researchers noted.

The findings were published April 20 in the journal Frontiers in Ecology and Evolution.

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moose hip with Osteoarthritis - Peterson (1).JPG
The hip bone of an Isle Royale moose that suffered from osteoarthritis.
Contributed / Rolf Peterson, Michigan Tech

Multiple case studies, such as the reintroduction of wolves in Yellowstone, have shown that the presence of wolves improves ecosystem health. Wolves keep prey populations, such as deer, elk and moose, in check, which benefits vegetation. Carcasses left behind by wolves provide food for other animals such as scavengers and redistribute nutrients.

But the Michigan Tech effort was the first to test the theory that wolves keep prey populations healthy by acting as a selective force against genetic diseases, said Sarah Hoy, one of the lead Michigan Technological University researchers on the project.

The research is an offshoot of the ongoing wolf-moose study that’s been underway for 63 years — the longest running predator-prey study in the world — that also includes John Vucetich and Rolf Peterson.

Selective predation by wolves can benefit the moose population not only by reducing the gene pool for impacted moose, but also by allowing healthy juveniles and healthy adult moose to keep reproducing and pass on their genetics, thus reducing the impact wolves have on overall population numbers.

“Osteoarthritis is a progressively crippling disease caused by deterioration of cartilage on the surfaces of moveable joints’’ such as knees and hips, Hoy noted. “As individuals get older, they are more likely to develop osteoarthritis and develop more severe forms of the disease.”

Young bull moose in fall2 - Hoy (1).JPG
A young bull moose on Isle Royale. New research shows that wolves do indeed show a preference for targeting old and diseased moose for their prey, leaving young moose like this one most likely to survive.
Contributed / Sarah Hoy, Michigan Tech

The presence of severe osteoarthritis, but not mild or moderate, increased the vulnerability of prime-age moose to predation.

“When it comes to wolves and moose, it makes a lot of sense that wolves would preferentially target moose that are in poorer condition because an adult moose weighs between 800 and 900 pounds, which is between eight and 10 times as heavy as a wolf,” said Hoy.

Researchers also found that the incidence of osteoarthritis in the moose population declined following years with higher kill rates by wolves.

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“The decline in osteoarthritis following years with more predation is, we think, because wolves preferentially removed moose with osteoarthritis from the population,” Hoy said.

The findings should give credence to the value of wolves as part of a healthy ecosystem, Hoy added.

“The management and conservation of wolves is controversial among the public. Yet our results suggest wolves might be an effective, natural and more ethical way of regulating the health of deer and moose populations — as opposed to using culls or recreational hunting to reduce the incidence of diseases or parasites of concern," she said. “The results are also relevant for policy-related arguments about reasons to refrain from intensively hunting wolf populations."

Wolves walking across ice - Peterson.jpg
Two Isle Royale wolves walking across ice. New research shows wolves on the island show a preference for preying on older and disabled moose.
Contributed / Rolf Peterson

63rd winter survey held this winter

After 62 years of annual surveys, Michigan Technological University researchers couldn't go to the island in winter 2021 because of COVID-19 concerns. But they were back this winter for the 63rd winter survey conducted from the air.

The moose herd was estimated at about 1,800 in early 2020, after the last full survey, but that number has almost certainly dropped dramatically since then with moose starving, unable to find quality food to eat. Researchers who went to the island in the spring said the state of the forest was the worst they had ever seen, with moose eating the forest faster than it could grow.

It's also unclear how many wolves now roam the island, but it's likely well over a dozen adults and many pups, all of them wolves relocated from Minnesota and Ontario and airlifted to the island in recent years, or offspring of those wolves. None of the island's original wolves remains.

Moose came to the island around 1900, peaking at 2,445 in 1995 and hitting bottom at just 385 in 2007. Wolves are relatively new to the island, having crossed the ice from the North Shore in 1949. Their numbers reached a high of 50 in 1980, and 24 wolves roamed the island as recently as 2009 before they crashed to just two when the wolf transplant began in 2017.

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At 45 miles long, Isle Royale is the largest island on Lake Superior, sitting about 14 miles off Minnesota's North Shore from Grand Portage. The island is a national park and mostly designated wilderness with few human visitors. There are no other major predators on the island; no human hunting is allowed; and moose are the only large prey species, making it a unique wild laboratory for the ongoing study.

The full research article can be found at frontiersin.org/articles/10.3389/fevo.2022.819137/full .

John Myers reports on the outdoors, environment and natural resources for the Duluth News Tribune. He can be reached at jmyers@duluthnews.com .

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Carpenter Thomas Spence's side job is capturing the essence of the wild along the North Shore of Lake Superior and the Superior National Forest.

John Myers reports on the outdoors, natural resources and the environment for the Duluth News Tribune. You can reach him at jmyers@duluthnews.com.
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