In the spring of 2017, University of Minnesota graduate researcher Tom Gable had a rare, surreal and as it turns out, fortuitous encounter with a wolf while he was tromping through the thick, swampy woods of far northern Minnesota.
He knew a wolf that researchers had outfit with a GPS tracking collar had been spending time in the area. As he approached, he spotted it splashing in a creek, only 30 feet away. So he quickly hid behind some shrubs, pulled out his iPhone and videoed the scene.
Eventually the wolf left, and Gable explored the area. He realized right away the wolf was hunting fish in the shallow stream. There were fish scales, blood and guts strewn around, with wolf tracks and scat everywhere.
The following year, Gable and his colleagues set up trail cameras, and captured additional video of two wolves from the same pack feasting on fish at the same spot.
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Scientists have long known that wolves on the Pacific coast hunt spawning salmon, but this was the first time researchers documented wolves eating freshwater fish to supplement their diet.
At the time, researchers assumed they had stumbled upon “a fluke of sorts, where a couple smart wolves had figured things out, and it was really a behavior restricted to those individuals,” said Gable.
He is now project lead with the Voyageurs Wolf Project, a University of Minnesota-led effort to better understand wolf ecology and predation habits in the summer — one of the biggest knowledge gaps in wolf research.
Not a fluke
Researchers have documented wolves fishing in and around Voyageurs National Park in six out of the past seven years. And they’re convinced that wolves elsewhere in Minnesota and in similar boreal forests in Wisconsin, Michigan and across Canada are also gorging on fish.
“And people just haven't known about it, because it's a really challenging behavior to document,” said Gable.
Researchers have found some wolves figure out how to hunt fish by themselves, while others learn it from their parents or older siblings.
“After observing males and females, yearlings and adults, lone wolves and pack members fish, we think that wolves hunt spawning fish across similar boreal ecosystems, and they likely have been doing it for quite a while. We don’t think it is a new behavior,” said Dani Freund, lead author on a new paper in the journal Royal Society Open.
GPS collars and trail cameras
This is the ninth summer that researchers have been conducting fieldwork, delving into the summer habits of wolves in and around Voyageurs National Park.
By placing GPS collars on wolves from seven different packs, they collect location data from the animals every 20 minutes, which allows them to zoom in on the animals' behavior at a finer scale than earlier versions of the collars had permitted.
When wolves spend more than 20 minutes at any one site, they know they're probably eating something.
Then they set up trail cameras at those sites to capture footage of wolves fishing, and other behaviors.
“We've got videos of wolves successfully catching fish and wolves waiting in ambush on creeks, trying to get fish, all sorts of really neat stuff,” Gable said.
They also recently started mounting GoPro cameras on some of the GPS collars they put on wolves. One of those wolves started to fish shortly after they placed that camera on it, Gable said.
“And we actually got video footage of that wolf eating several freshly caught fish. So a lot of these different pieces of information have come together to kind of tell us this larger story.”
Some other intricacies of when, how and where wolves fish that researchers uncovered include:
Wolves fish almost exclusively at night. They appear to mainly use their ears to find fish, not their eyes. When a fish breaks the surface of the water, “that's what allows them to launch an attack, rather than seeing them,” Gable said. “So wolves appear to be keying or cueing in on that sound.”
They fish from April to June, when suckers swim in masses up rivers and streams to spawn. Fish splash more and are distracted when they lay their eggs. That makes it easy for wolves to detect their prey and catch them.
Wolves fished in creeks, rivers, and streams less than three feet deep, often in the shallow waters below beaver dams. The dams create barriers for fish as they swim upstream to spawn. That can cause a “fish traffic jam” that researchers say wolves then use to their advantage.
Researchers surmise that wolves may be keying in on fish when they spawn in part because it’s a relatively risk-free diet.
“Wolves' main weapon is their mouth, so going after prey such as deer can cause a severe injury,” said Freund. “Fish on the other hand can’t do much to a wolf, and wolves seem to be taking advantage of that. Some wolves seemed to completely pass up larger prey such as beaver when fish were available and abundant.”
A larger menu
Wolves aren't fishing all summer. They appear to focus intensively on fish during a two to three week window when suckers spawn, said Gable. When that food source disappears, they turn to other options.
Other novel research already published by the Voyageurs Wolf Project has documented that wolves in and near the park also eat a large number of beaver, and that they hunt them, not by chasing them, as they do deer, but by lying stealthily in ambush, sometimes for hours.
Wolves are also omnivores. They will gorge on blueberries when they ripen to supplement their diet, which still relies heavily on deer.
“If you think about wolves as a species more broadly, they occupy so many different habitats: deserts, the Arctic forests, mountains, plains,” said Gable. “And it's probably this ability to take advantage of unique food sources that has allowed them to occupy all these really unique habitats.”
Another big takeaway for Gable is that even with the advancements in technology that have made their project possible, wolves often outsmart them. He said when they go out in the field to place new trail cameras to document their activity, such as fishing, wolves often sense that humans were there, and will move to another spot.
“But every once in a while, you get a clip that's a real gem and you're like, ‘Oh my gosh, can you believe that?’ So that's kind of stuff that keeps the work really exciting.”