Wolves might help moose avoid acquiring a deadly parasite from deer, study shows

FOR IMMEDIATE RELEASE 

ST. PAUL, Minn. — Higher densities of predators on the landscape caused deer and moose to use less of the same habitat, decreasing the likelihood of a parasite spilling from deer to a vulnerable moose population, according to a new study led by scientists from the University of Minnesota and the Grand Portage Band of Lake Superior Chippewa.

The parasite they were interested in is called Parelaphostrongylus tenuis, a brainworm mostly harmless to deer but fatal to moose. The researchers found that predator pressure by wolves on the Grand Portage Indian Reservation in Northeastern Minnesota changed how deer and moose used the landscape; higher wolf pressure was linked to less overlap between deer and moose and a lower risk of parasite transmission.

The study, published this week in the journal Science Advances, offers a new theory on the role of predators in disease transmission among prey. While it’s understood that predators like wolves can directly reduce disease among their prey by killing those infected, these findings suggest that wolf influence on cervid movements and habitat choices might indirectly reduce parasite transmission.

The results could have broad implications. Twenty-three percent of collared moose that died in Northeastern Minnesota in the past 15 years were infected with P. tenuis. During that period, the region’s moose population declined by half, from about 10,000 to about 5,000. Further, more and more deer are making their way onto moose range throughout the U.S., which leads to increased concerns of spillover of P. tenuis and other infectious diseases—such as chronic wasting disease.

The findings give state and tribal managers new information to consider in drafting and implementing herd and wolf management plans in Minnesota and beyond. Maintaining healthy moose populations is a central goal of tribal managers, as moose are an important subsistence species for the Grand Portage Band and important to cultural preservation.

The scientists had a unique data set to study. The Grand Portage Band and University researchers have for years been studying moose in an effort to understand and reverse a long-term moose population decline. Between 2007 and 2019 they trapped and collared more than 200 deer, moose, and wolves on the Reservation in Northeastern Minnesota for a broader ecosystem health project. For this latest project, they sought to learn the 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.

The researchers, led in part by wildlife epidemiologist and principal investigator Tiffany Wolf, DVM, PhD, in the Department of Veterinary Population Medicine (VPM), found that amid typical wolf pressure, deer and moose used the landscape differently from one another. For example, during the winter deer favored lowland areas while moose favored highland areas; the reverse became true during the spring migratory period. But the researchers also wanted to know how the cervid movements might change if there were fewer wolves on the landscape. What they found in that case was deer and moose were more likely to overlap—especially during the spring and summer when the parasite spreads—increasing the chance of spillover.

“We often think of wolves as bad news for moose because they kill a lot of calves,” Wolf said. “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.”

RELATED: Newly funded: Understanding the shifting environmental factors affecting moose

Among other implications, the findings illustrate that the dynamics of disease in the wild may change with the loss of carnivores like wolves and with landscape disturbances caused by nature or humans.

“Understanding the effects of managing predators and prey on the landscape is an area of research that needs considerable attention in an experimental fashion,” said Seth Moore, director of biology and environment for the Grand Portage Band and co-principal investigator of the project. “The results of the study really illustrate that predator-prey dynamics may impact wildlife disease and overall ecosystem health. Our applied research to restore moose in Minnesota will incorporate this new and important area of study for ecologists and epidemiologists by using approaches that combine predator-prey dynamics with the interactions of disease.”

Moore added that many factors can influence how deer and moose use the landscape, and in this study the team chose to look at predators. From an ecology perspective, more research is needed to fully understand all factors influencing the behavior of these species in Northern Minnesota and how managers can leverage that understanding to benefit moose.

Current models of disease transmission in the wild are based on a general distribution of deer and moose and often assume the animals move randomly. That scientists now know habitat choices might be predicated on wolf movements could reshape expectations of wildlife disease transmission. 

Key to the study were Moore, Edmund Isaac, and Yvette Chenaux-Ibrahim, of the Grand Portage Band; Luiz Gustavo Oliveira-Santos, of the Federal University of Mato Grosso do Sul, Brazil, who provided spatial ecology expertise; Virginia Tech assistant professor Luis Escobar, in the Department of Fish and Wildlife Conservation; William Severud and Tyler Garwood in the VPM department; and James Forester in the University’s Department of Fisheries, Wildlife, and Conservation Biology.

Funding was provided by the Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources; the U.S. Fish and Wildlife Services Tribal Wildlife Grant Program; the U.S. Bureau of Indian Affairs; the U.S. EPA Great Lakes Restoration Initiative; the Minnesota Zoo Ulysses S. Seal Conservation Fund; the Indianapolis Zoo Conservation Grant; and the Van Sloun Foundation.