Science, field investigation in action
Biologists with NMU ties find wolves eat fish, berries
MARQUETTE — White-tailed deer and beavers are prey animals of wolves, but the wolf diet might be more varied than previously thought.
A team of biologists, including Northern Michigan University alumnus Tom Gable (’16 MS) and master’s student Austin Homkes, has documented a pack of wolves in Minnesota’s Voyageurs National Park that hunts fish as a seasonal food source.
They even captured some night-vision video of the activity. This discovery, along with earlier studies through the Voyageurs Wolf Project, suggests the animals’ diets are different from earlier beliefs.
“Arguably even more interesting was that during Tom’s master’s work, berries (mostly blueberries) were an important part of the diet of one of the other wolf packs for several weeks during the summer,” biology professor John Bruggink, who has conducted research with both men, said in a news release.
Bruggink said Gable’s master’s thesis at NMU focused on wolf predation in and around Voyageurs. One chapter described the sites where wolves kill beavers and the other addressed biases in scat-based diet studies.
Homkes is in his second year as an NMU graduate student and is also working in and around the national park. But he is researching wolf predation on white-tailed deer fawns instead of beavers.
“These aspects of wolf ecology have historically been difficult to study because, unlike with adult deer and moose, wolves can consume small animals like beavers and fawns quite quickly and almost completely,” Bruggink said. “Tom and Austin managed to pull this off by combining cutting-edge technology in the form of global positioning system radio collars that provide very frequent locations via iridium satellites, with good old-fashioned investigative field skills for examining possible kill sites.”
Gable is pursuing his doctorate at the University of Minnesota. His NMU thesis results have been published in four papers co-authored with Bruggink in peer-reviewed journals; Homkes is listed as a co-author on one.
They address the following topics: weekly summer diet of gray wolves in northeastern Minnesota; estimating biomass of berries consumed by gray wolves; where and how wolves kill beavers; and confronting sampling method biases in wolf diet studies.
In a Dec. 17 feature for Minnesota Public Radio, reporter Dan Kraker wrote that in April 2017 Gable trekked to a creek where a collared wolf had spent a good deal of time. Searching for evidence of a kill, Gable saw a collared wolf — that didn’t see him — 50 feet away.
Gable watched the wolf move back and forth around the creek for the next 15 minutes, periodically running into the creek and splashing around. The wolf stopped and looked like it was eating something, and then went back to the creek.
Gable discovered the wolf was hunting spawning suckers.
“And then as I explored the area even more, I found wolf tracks all over the mud on the creek, and I found fish scales and blood and guts all over the edges of the creek, and you could just see that wolves had been spending a lot of time there,” Gable was quoted as saying. “And there were wolf scats as well that were full of fish scales and fish remains.”
A month later, researchers found the two GPS-collared wolves in the Bowman Bay pack spent about half their time hunting fish there, according to the article, and about a year later, Gable and his colleagues noticed the pack visiting the creek again. They then set up trail cameras, and caught footage of the wolves fishing at night.
The Voyageurs Wolf Project wrote a Dec. 18 post on its Facebook page that addressed the mammal’s berry-eating habits. It read in part: “Well, we are here to tell you it is true! In July and August, wolves spend considerable time in areas with abundant berries. During this July-August period, berries can make up to 80 percent of the weekly diets of wolves.
“Now, this doesn’t mean that wolves prefer berries over their typical prey, but rather that in July-August wolves’ typical prey (deer fawns and beavers) are harder to catch and so wolves turn to a food source that is abundant and requires little energy expenditure.
“However, there are trade-offs. Berries have 3.75 times less energy per pound than meat which means that wolves have to eat a lot of berries to get the same amount of energy. In addition, it doesn’t seem wolves have a digestive system that is great for digesting berries.
“We are continuing to study what role berries may or may not be playing in the summer ecology of wolves! We should have some exciting news to report on this in the next year or so!”
The project’s Facebook page also includes the video footage of the wolves hunting freshwater fish, giving credit to its collaborator: Fisheries, Wildlife and Conservation Biology-University of Minnesota.