Research reveals more secrets of where wolves hunt in northern Minnesota and their impact on forests
Research published in the past month by scientists with the Voyageurs Wolf Project reveals further insights into how and where wolves in far northern Minnesota hunt for their prey, and how in some cases that hunting can have a profound impact on the region’s forests.
One study builds on past research that demonstrated how wolves living in and around Voyageurs National Park eat large numbers of beaver, and by doing so can significantly shape the ecosystem by influencing the creation of wetlands.
The new findings estimate that wolves, by ambushing beavers when they stray far from water in search of trees to eat, can also have an impact on the land, by altering the trajectory of nearly three percent of the boreal forest in the Voyageurs area.
Meanwhile, a second paper identified a strong link between human development and where wolves successfully hunted deer fawns. The research suggests that people in northern Minnesota may inadvertently have aided wolves in their search for food.
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“When we put all of the pieces together, it is pretty clear that the cumulative effects of all major aspects of human activity in the Northwoods — logging, infrastructure development, and road/trail development — have fundamentally changed where and how wolves hunt deer fawns here,” said Sean Johnson-Bice, a PhD candidate from the University of Manitoba and one of the lead authors of both studies.
“The rules of this predator-prey game change when people alter ecosystems, and it’s possible we have created conditions that may have tipped the scales in the predators’ favor.”
Tracking wolves
For the past decade, researchers have combined cutting-edge technology — GPS collars and trail cameras — with countless hours of sweaty, buggy field research to gain a better understanding of how wolves hunt during the summer months in the dense, boreal forest of northern Minnesota.
Most past studies of wolf predation have been conducted in the winter, when wolves are easier to track, and when they hunt in packs for large prey such as deer.
Every spring, researchers place GPS collars on about a dozen wolves in their study area. The collars send a location signal every 20 minutes.
Whenever a wolf spends more than 20 minutes in the same spot, scientists hike in to investigate. They know it’s likely a place where the wolf ate something. They gather evidence like forensic scientists, and sometimes set up trail cameras to help document future activity.
Over the years they’ve uncovered some surprising predation behavior, including that wolves hunt freshwater fish, gorge on berries and kill a surprising number of beavers, often by waiting, sometimes for hours, to ambush beavers as they leave their ponds in search of forage.
Now, in a study published earlier this month in Proceedings of the Royal Society B, researchers found that wolves disproportionately kill beavers the farther away from water that they venture, thus helping to preserve the forest farther away from beaver ponds.
The study examines what happens to the surrounding ecosystem when an apex predator, a wolf, meets up with a beaver, a major ecosystem engineer that shapes forests by cutting down trees and creates wetlands by damming creeks.
Beavers in northern Minnesota create a network of well-defined trails emanating out from the ponds where they live. They travel along these trails to forage for food. And they can have profound impacts on the makeup of the surrounding forest.
Beavers prefer to eat deciduous trees, such as aspen, often leaving evergreen conifer trees standing. Over time, as beavers eat more and more deciduous trees close to the water, that creates what are known as “conifer halos” around ponds, easily seen from above.
In this study, researchers found the farther beavers ventured away from ponds in search of food, the more likely they were to be killed by wolves.
They searched nearly 28,000 clusters of GPS locations from 51 collared wolves, documenting nearly 2,000 ambushing attempts by wolves, and more than 500 beavers killed by wolves.
“Basically what they’re doing, through just their basic presence and predation, is allowing certain forests to remain undisturbed by beavers,” explained Tom Gable, a University of Minnesota researcher who leads the Voyageurs Wolf Project.
For Gable, while the study may not demonstrate wolves are dramatically altering forests on a wide scale, he said it does illustrate wolves “are connected through predation to larger ecological processes. And that just shows how in the natural world, everything is in some way to a degree connected.”
Hunting near people
Scientists also found that the actions of people can have a profound impact on where wolves hunt in northern Minnesota.
That was the finding of another paper recently published by many of the same authors in Ecological Applications. In it researchers documented how wolves utilize roads and trails to hunt deer fawns, that they hunt more often in recently logged areas, and that they hunt close to homes and resort areas where deer congregate.
In fact, the researchers found kills were much more likely to occur closer to buildings than random locations in the forest.
“Surprisingly, wolves tend to kill deer fawns closer to human infrastructure, like cabins, year-round residences, and barns, than expected,” said Johnson-Bice from the University of Manitoba and co-lead author of the study.
The finding seems to contradict a long-held theory called the “human shield hypothesis,” which holds that prey will congregate close to people as a refuge or safe haven from predators, to take advantage of the fact that most predators, including wolves, have a fear of humans.
“And so if we would expect that to be happening in our study area, we would have expected to find wolves killing deer fawns predominantly farther from infrastructure, but we found the opposite pattern,” said Johnson-Bice.
Researchers are quick to point out that there is no evidence wolves in their study area near Voyageurs National Park have lost their fear of humans. They say they are rarely seen near the resort communities of Ash River and Kabetogama.
Researchers suspect that means wolves are entering those areas at night to hunt to avoid detection.
They also hypothesize that they are coming close to humans because that is where the deer are gathering, likely at least in part because many people feed deer, especially during the winter.
“And we think that almost certainly congregates deer around the neighborhoods. And at the end of the day, predators are going where the deer are,” said Johnson-Bice.
Researchers also note that they didn’t look at the rates of predation; they didn’t assess whether wolves were killing more deer fawns than they would otherwise. Rather, they analyzed where wolves are killing fawns.
They also noted wolves disproportionately hunted and killed deer fawns in areas of the forest logged within the past five years. Those areas provide important forage for deer, as well as dense thickets of young saplings that provide excellent hiding spots for fawns.
Scientists also found that wolves preferentially hunt fawns along “linear” features, including power line corridors, logging roads and ATV trails. Researchers say that makes wolves more efficient predators.
“Just like humans, wolves often prefer to travel on linear corridors like roads and trails rather than bushwhacking through the dense forest,” said John Bruggink, a professor at Northern Michigan University, and a co-author of the study.
Through trail camera footage collected over several years, researchers also gathered evidence that wolves weren’t only using roads and trails to travel, but that they also served as hunting grounds, indicating that deer also used them as travel corridors.
Gable said the findings from the project over the past decade — which now include about two dozen published papers — are possible not only because of improved technology, but also because of the length of the project, and funding from the state’s Environment and Natural Resources Trust Fund, and other sources.
“I think as time goes on, we're able to collect better data on how humans are connected to these patterns and processes,” Gable said. “We hope to kind of unravel that a bit more.”