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Wolves may help keep deer, and brainworm, away from moose

Study on the Grand Portage Reservation sheds light on complex wildlife relationships.

Bull moose on Grand Portage Reservation
A bull moose feeds in the forest of the Grand Portage Reservation. A new study found that having wolves in an area helps keep moose and deer apart, reducing the risk that deer will spread a parasitic brainworm to moose.
Contributed / Seth Moore

Could having wolves in the area help keep deer and moose apart, and thus spare moose from a deadly parasite that’s spread by deer?

That’s the finding of a new study by University of Minnesota and Grand Portage Band scientists who found that having wolves around caused deer and moose to split up more, decreasing the likelihood that deer will spread parasitic brainworm to moose.

The study found that higher wolf pressure was linked to less overlap between deer and moose and a lower risk of parasite transmission, the study noted.

While moose have coexisted for centuries with wolves around, they didn’t have to deal with white-tailed deer much until the last century. Especially in the last 50 years, deer have moved farther north into moose territory, and the deer have brought along a parasite called P. tenuis. The parasitic brainworm is harmless to the deer but nearly always fatal to moose, and it’s considered a critical factor in why northern Minnesota moose have declined dramatically.

The study, published last week in the journal Science Advances, was headed by Tiffany Wolf of the University of Minnesota and Seth Moore, director of biology and environment for the Grand Portage Band of Lake Superior Chippewa.

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Tiffany Wolf, a wildlife veterinarian with the University of Minnesota's Department of Veterinary Population Medicine, works on a wolf that's part of ongoing research on the Grand Portage Reservation into the links between, wolves, deer, moose and habitat — all aimed at recovering the regions' beleaguered moose population.
Contributed / Seth Moore

Researchers found that, with typical wolf pressure, deer and moose used the landscape differently. During the winter deer favored lowland areas while moose favored highland areas. But the researchers also wanted to know how the animal’s behavior might change if there were fewer wolves on the landscape.

During periods when fewer wolves were around, deer and moose were more likely to overlap, increasing the risk that moose would pick up brainworm from the deer.

“We often think of wolves as bad news for moose because they kill a lot of calves,” Wolf said in a statement. “But this (study) suggests that wolves may provide a protective benefit to adult moose from a parasite-transmission perspective. Because brainworm is such an important cause of adult moose mortality in Minnesota, we can now see that the impact of wolves on moose is a bit more nuanced.”

The results could have broad implications. Some 23% of radio-collared moose that died in Northeastern Minnesota in the past 15 years were infected with P. tenuis. In the Grand Portage study area, the brainworm kills as many as 35% of the adult moose, Moore said. Over those 15 years Northeastern Minnesota’s moose population plummeted from about 10,000 to about 5,000. Brainworm was also a culprit in the complete collapse and elimination of the northwestern Minnesota moose herd in the 1990s.

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Meanwhile, more deer are making their way into moose range throughout the northern U.S., which leads to increased concerns of spillover of P. tenuis and other problems, including liver flukes and chronic wasting disease, both carried by deer.

And having a lot of deer in the area also encourages more wolves. Northeastern Minnesota has among the highest wolf densities anywhere in the world, higher than Alaska or Canada, because wolves thrive more on easy-to-kill deer than they do on larger prey.

“And having those deer keeping the wolf population... higher is also a huge problem for moose calves. Because in May, when the moose calves come out, they are the easiest things in the woods for a wolf to kill. Even easier than a deer,” Moore said. “That’s why we're seeing zero calf recruitment.”

That means almost no moose calves survive to become adults.

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The Grand Portage Band and University researchers have for years been studying moose in an effort to understand and reverse Minnesota’s long-term moose population decline. Between 2007 and 2019 they trapped and collared more than 200 deer, moose and wolves on the Grand Portage Reservation at the tip of Minnesota’s Arrowhead region, in Cook County. In the latest research, the scientists were looking at seasonal migratory patterns of deer and moose, and how the risk posed by wolves to those animals might affect those patterns and influence the transmission of brainworm.

Moore said the study shows the complex relationship between the three species and noted that any effort to save Minnesota's dwindling moose population may require intensive deer management and, at least to start, targeted wolf management.

“I think if we can agree on an area in the core moose range where we are going to work to benefit moose, and we include deer management and maybe some wolf management to start, along with targeted habitat work, we might succeed,” Moore said. “We might be able to keep moose in Minnesota.”

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