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Serving Northern St. Louis County, Minnesota

Wolf predation may reduce brainworm frequency in moose

Predators appear to encourage segregation of moose and deer

Marshall Helmberger
Posted 1/19/22

REGIONAL— It turns out that gray wolves may not be all bad when it comes to northeastern Minnesota’s moose population. A new study published last month by University of Minnesota and …

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Wolf predation may reduce brainworm frequency in moose

Predators appear to encourage segregation of moose and deer

Posted

REGIONAL— It turns out that gray wolves may not be all bad when it comes to northeastern Minnesota’s moose population. A new study published last month by University of Minnesota and Grand Portage Band researchers suggests that wolf pressure can actually help to reduce the incidence of the parasitic brain worm, known as P. tenuis, among adult moose.
The brain worm, which is carried by white-tailed deer, is a significant contributor to adult moose mortality. Indeed, 23 percent of collared moose that died in northeastern Minnesota over the past 15 years were infected with the brain worm. That’s a significant impact to the region’s moose population, but it’s an impact that pressure from gray wolves may actually help to reduce.
While moose and white-tailed deer generally spend their time in different habitats, both species demonstrate some seasonal migration, especially ahead of winter. During spring migration and during summer, the two species are more likely to intermingle the study found— and that’s when moose are most likely to fall victim to brain worm infection.
Increased predation pressure from gray wolves, it turns out, had the effect of increasing the segregation of deer and moose across their various habitats. More segregation leads to less opportunity for moose to contract the brain worm.
The brain worm is harmless to white-tailed deer, since the parasite spends its life in a host white-tail residing in the tissue immediately surrounding the animal’s brain. White-tails expel brain worm larvae through their feces. The deer droppings are subsequently fed on by land snails, which ingest the larvae. Moose accidently ingest the snails as they browse on forest plants, and once ingested, the developing larvae migrate toward the moose’s brain. Unlike with white-tailed deer, where the worm is content to reside just outside the brain, with moose, the worm burrows into the brain, gradually consuming portions of it. Eventually, most moose succumb to the effects of the parasite.
The study was conducted in and around the Grand Portage Band of Lake Superior Chippewa Indian Reservation in Cook County, where U of M and Grand Portage researcers have been studying moose in an effort to understand and reverse a long-term moose population decline. Researchers captured and tracked 94 adult moose, 89 deer (65 adults) and 47 adult wolves during the 2007–2019 study period.
“We often think of wolves as bad news for moose because they kill a lot of calves,” said principal investigator Tiffany Wolf, DVM, Ph.D., an assistant professor in the Department of Veterinary Population Medicine. “But this 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 findings give state and tribal managers new information to consider in drafting and implementing herd and wolf management plans in Minnesota and beyond.