Unlikely food source may be behind moose success at Voyageurs Park

©Star Tribune (Minneapolis)

Brian Peterson/Minneapolis Star Tribune/TNS

Deep in the woods of Voyageurs National Park, on the remote Kabetogama Peninsula just south of Rainy Lake, a small and isolated moose population is surviving, even as others in Minnesota have been cut in half or wiped out.

The moose inside the park have been dealing with the same challenges as those outside it, from disease to predators to warming temperatures, yet their numbers today are almost identical to what they were in the early 1990s. The question is, why?

A team of wolf researchers, which has been painstakingly documenting every summertime kill and meal for wolves in the park, believes the answer may be because Voyageurs moose have a robust ally — or, perhaps, a sacrificial pawn — that others don’t: American beavers.

Beaver numbers are so strong inside the national park that they’ve become the primary food for many of the park’s wolves in the summer. It’s possible that the beavers, once hunted to the brink of extinction, are keeping the wolves fat and happy enough that the predators don’t need to eat the moose or their calves, said Tom Gable, project lead for the Voyageurs Wolf Project, a group of researchers with the University of Minnesota and the National Park Service studying summer wolf habits.

There are no easy meals in the wild. “But, relatively, it is much easier for them to catch a beaver than to risk getting kicked by a moose,” Gable said.

With fewer calves being eaten, a higher percentage of moose may be living long enough to breed, keeping numbers stable even as the population deals with the same threats and diseases that plague moose in the rest of the state, Gable said.

The surprising thing is that Voyageurs has a relatively large wolf population. But, for whatever reason, the wolves inside the park almost never eat or kill moose in the spring and summer, when calves are at their most vulnerable, Gable said.

“We’ve tracked and found over 800 kills of beavers and deer fawns and everything else wolves are eating,” Gable said.

Out of all of those kills, only three were moose.

A tempting alternative

Beavers are treated like a nuisance throughout much of the state. The same front teeth and engineering skills that allow them to build intricate dams and ponds for their young can also cause flooding in developed areas, kill off timber and reroute or choke popular trout fishing streams.

When their dams cause damage or threaten property, trappers come in and the dams are destroyed. But inside the park, beavers have flourished for 50 years among nearly 200 square miles of untouched aspen and birch trees. Their population in the park, estimated to be more than 3,000, makes Voyageurs one of the largest and densest beaver habitats left in the Midwest. They are up to 10 times more abundant in the park than elsewhere in the state, according to U research.

Growing up to 60 pounds, an adult beaver can make quite a meal for a wolf, Gable said.

The researchers and volunteers with the Voyageurs Wolf Project have been combing the national park for about seven years, tracking dozens of wolves and wolf pups to learn more about how they survive and act before snow is on the ground. Until recently, little had been documented about their summer behavior.

They’re difficult to track because they stop hunting in packs and are often on their own, blending in almost perfectly with the brush and traveling incredible distances, Gable said.

Their kills in the summer, when food is plentiful, are much less dramatic, and much less evidence is left behind than when a pack takes down a moose or a deer in the winter.

Researchers using GPS collars and trail cameras can record everywhere a wolf goes. Each time a wolf stays put for longer than 20 minutes, a member of the team hikes to that location to look for remains of what the wolf just ate.

The project made national news when it found that not only are wolves proficient at fishing, they actually set the fish aside, stockpiling them while the fishing is good and eating them when it slows down. Cameras also caught wolves eating blueberries and regurgitating those berries for their young.

What has become apparent, Gable said, is that wolves prefer to ambush and eat beavers than to try to chase moose and their calves.

Careful balance to study

Over the next several years, researchers plan to study exactly how moose populations correlate with beavers and wolves.

Careful study is needed because it’s possible an abundance of beavers could actually harm moose populations, Gable said. More beavers in the spring and summer could create more food for wolves, allowing more to survive into the winter, when they are forced to eat more moose once the beavers are hidden in their icy dams.

But, at least early on, the health and stability of moose populations inside Voyageurs seems to point to the benefits of having beavers around to distract and satiate wolves while moose are at their most vulnerable.

If it turns out that beavers can help, it could give state and federal wildlife officials a new tool for bringing back the giant grazers.

In the early and mid-2000s, moose numbers plummeted across the state, dropping from as many as 9,000 to somewhere in the range of 3,000 to 4,000 animals, though it has stabilized since then. The Minnesota Department of Natural Resources (DNR), which conducts a winter population estimate every year, believes the numbers have held relatively flat since 2011.

Researchers point to a number of reasons for the decline, including habitat loss and rising temperatures, as well as growing wolf populations. One of the biggest threats is the spread north of a parasitic brainworm.

But it might not take much for moose to turn the corner. If just a few more females survived to breeding age and a few more calves made it to maturity, the population could start rising again, said Glenn DelGiudice, DNR moose project leader.

Calves are at their most vulnerable in the first 30 to 50 days after they’re born in spring, DelGiudice said.

“All of a sudden in the first two or three weeks of May, there will be thousands of deer fawns and moose calves on the landscape in northern Minnesota,” DelGuidice said. “It’s like a smorgasbord for wolves and black bears, who are just out of hibernation.”

About 65% of calves born in Minnesota die before they reach a year old, according to a recent DNR study. Most of those calf deaths — 60 to 70% — are caused by wolves.

Except in Voyageurs, where, smorgasbord or not, the wolves seem content to hunt beavers and occasionally fish or snack on blueberries.

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