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The Secret Fish Trees at Northwood's Wolves: NPR



New research at Voyageurs National Park challenges the conventional wisdom of wolves: Their diets are much more varied than previously thought.

Courtesy of Voyageurs Wolf Project


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Courtesy of Voyageurs Wolf Project

New research at Voyageurs National Park challenges the conventional wisdom of wolves: Their diets are much more varied than previously thought.

Courtesy of Voyageurs Wolf Project

Wolves, as it turns out, may not be the bloodthirsty, moose, nordwoods roaming predator you always thought they were.

New wolf package research at Voyageurs National Park in Northern Minnesota challenges conventional wisdom On wolves: Their diets are much more varied than previous researchers.

Scientists with the Voyageurs Wolf Project, a collaboration between the park and the University of Minnesota, have for the first time documented wolves hunting freshwater fish as a seasonal food source – and they have video to prove it.

A diet of meat and berries

Wolves are still dependent on deer, but previous studies on wolves in the park have shown that they also eat a large number of beavers – and even blueberries – to supplement their diet .

Wolf scat shows evidence of blueberries in the diet.

Courage of Tom Gable with Voyageurs Wolf Project


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Court of Tom Gable with Voyageurs Wolf Project

Wolf scat shows evidence of blueberries in the diet.

Courtesy by Tom Gable with Voyageurs Wolf Project

These new discoveries, recently published in the journal Mammalian Biology were possible thanks to new technology.

Since 2015, researchers have placed the GPS collar on wolves from seven different packages in and around the park. They collect site data from the animals every 20 minutes, allowing them to zoom in on the animal's predation habits on a finer scale than previous versions of the collar had allowed: When wolves spend more than 20 minutes in any place, they know they probably eat something.

It was like they first suspected members of the Bowman Bay package were eating fish. In April 2017, the University of Minnesota researcher Tom Gable walked to a stream where one of the colleague wolves had spent much time. He searched for evidence of a death.

He looked up and saw a checked wolf about 50 meters away. But the wolf didn't see him.

"It was really crazy," he said. "He came within about 8 to 10 meters of me and he had no idea I was there. I hid in the bushes on the edge of this bay."

Over the next 15 minutes, Gable saw the wolf back and forth around the stream. Periodically, it would run into the stream and splash around. Then it stopped and looked like it was eating something before returning to the brook.

Eventually the wolf left and Gable came out to hide to explore the area. He immediately realized that the wolf was hunting for fish – shaking suckers – in the pelvis.

University University of Minnesota Researcher Tom Gable gathers the skull / jaw of a beaver killed by a wolf.

Honor of Tom Gable


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Court by Tom Gable

University of Minnesota scientist Tom Gable gathers the skull / jaw of a beaver killed by a wolf.

Courtesy of Tom Gable

"And since I explored the area even more, I found wolf tracks all over the clay on the pelvis and I found fish scales and blood and intestines over the edges and could only see the wolves having spent much time there," he said. "And there were also wolf mushrooms full of fish scales and fish remains."

Gable and his colleagues quickly learned that the little scene he witnessed was not just a one-time meal. During the month following their migration to the bay, the researchers found that the two GPS collars in the Bowman Bay package spent about half their time hunting fish there.

A year later, Gable and his colleagues noted the pack that visits the brook again, so they set up track cameras and caught traces of the wolves at night.

"You can see the wolves suddenly head to the water several times after hearing a splash," Gable said. "They learned what a fish is splashing in the stream sounds like and they know it means food."

The video also captured wolves that catch fish and do not eat them immediately. Instead, they stored them on the stream's beach and fished a little more.

That behavior gives a glimpse of a wolf's mental processing, Gable says. "It knew in some way that it would be more, so it might as well be getting fish while fishing was good and then coming back to the fish after he got what he could".

A first for freshwater fishing

Scientists have long known that wolves in coastal habitats in British Columbia and Alaska eat spawn. But this is the first time that a similar behavior with hunting freshwater fish has become detailed.

"Given the impressive adaptability of wolves to find food, it is not entirely surprising," says project consultant Joseph Bump.

But wolves are elusive, he said: "Especially in the dense forest areas in northern Minnesota you must either be in the right place at the right time or have access to GPS collar data. "

These collars have helped push new light into the wolf's secret life in the dense boreal forest of northern Minnesota. Scientists map out 68,000 GPS sites that the packages visited just this past summer.

A package of wolves on a frozen lake in Voyageurs National Park.

Courtesy Voyageurs Wolf Project


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A package of wolves on a frozen lake in Voyageurs National Park.

Courtesy Voyageurs Wolf Project

Among their great finds so far have been:

  • Wolves omnivores. They eat a lot of blueberries in July and August. When the fruit matures in northern Minnesota, deer groats – the wolf's primary prey in June – are old enough to get away.
  • Wolver eating beaver – many of them. Beavers can account for up to 42 percent of a packaging diet from April to October, researchers have found. Preliminary data show that on average one wolf in Voyageurs kills about six to eight beavers per year. But it varies. Individual wolves cannot eat any beaver at all. But they found a wolf that had eaten 28 beavers in a year.
  • Wolves hunting shifts differently than they do other prey. Instead of chasing them, they lie in ambush and strike when the beaver wins on land.
  • The wolves are good swimmers. A watched wolf swam 12 times over parts of Rainy Lake over a two day period covering 2.6 miles.

All these results help to confirm what researchers have understood for a long time: Wolves are highly adaptable creatures, and therefore they have succeeded in so many different habitats, from North America to Europe to Asia.

"Wolves are opportunistic. They can be adapted quite easily to new food sources," explained Steve Windels, an animal biologist at Voyageurs National Park.

Nevertheless, he acknowledged that it is exciting to confirm behaviors suspected by researchers, especially in Minnesota wolves that have not been studied as intensely as their counterparts in Yellowstone National Park and elsewhere.

One of the remaining details Windel hopes to tease is the complex relationship between the wolves' predation on beaver, deer and moose and the impact it has on their populations.

Voyageurs is unique because it has one of the densest populations of beavers in the region. It is also one of the only places in Minnesota where the moose population stays steady. In other parts of northeastern Minnesota, the moose has declined sharply over the past decade for many reasons, including diseases and other health-related causes, but partly due to wolf spreading.

It is still too early to make a direct tie between Voyageur's permanent moose population and its abundance of beavers for wolves to feed on, Windels said. But "this is an excellent opportunity for us to really get that question just because of the density of beavers we have here, we create a unique laboratory where we can actually begin to see how that dynamics play."

Meanwhile, wolf research at Voyageurs has received a lot of attention. A new Facebook post that maps the various wolf package areas in the park has drawn over 500,000 views, Gable says.

"It's really a satisfying part to do all this is to share what we actually find with people and to see how excited people are about the work we do."


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