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Studying elusive wolves in northern Minnesota is always challenging, but tracking their eating and movements has typically been easier in winter.

Wolves travel in packs this time of year, hunting large prey such as deer and moose. With bare trees and a blanket of white spread over the ground, it’s easier for observers to watch the wild canines and spot evidence of carcasses left from their meals, even from the air.

But when the forest thickens up in the summer and wolves have pups, the packs separate and the wolves travel mostly alone. They eat smaller animals and almost completely devour them, leaving little evidence for researchers to find.

In recent years, the University of Minnesota and Voyageurs National Park have been collaborating on intensive summer ecology research on wolves, using real-time data from GPS collars to set up trail cameras in strategic places.

The research led to the discovery published recently that blueberries may play a more important role in the canines’ diet than researchers knew.

Not only do wolves eat berries — something researchers were already aware of — but adult wolves also regurgitate them to feed their pups.

“That had never been seen before,” said Tom Gable, a lead researcher and a Ph.D. student with the U’s Department of Fisheries, Wildlife and Conservation Biology.

The observation also raises more questions: Are wolves using the berries out of desperation to survive at a time when deer are well-fed and can outrun them? Or are they recognizing berries as an abundant food source that takes less energy to find?

“We don’t really think of wolves as omnivorous animals, necessarily. We think of them as carnivores,” Gable said. “But they are flexible.”

Researchers found evidence of berries in wolf scat previously, Gable and others said.

In 2017, researcher Austin Homkes went to a drained beaver meadow near the national park after learning from GPS collars that it was a “wolf rendezvous site.” He saw five pups gather around an adult wolf that was regurgitating food for them.

About a half-hour after they moved away, Homkes went to the spot where they had been standing and found small piles of chewed and whole wild blueberries mixed with stomach fluids.

Previous researchers had thought pups were eating the berries themselves, but Homkes’ observation means that adults were recognizing the berries’ value for their young, too.

The discovery “provides another example of the potential importance of berries as a food source for wolves,” the researchers wrote in a paper published recently in the Wildlife Society Bulletin.

Gable and colleagues captured the berry-eating on camera last summer after looking at GPS collar data and finding the wolves in one pack were spending a lot of time in an area with berries.

In late June, they went to the spot and put up more than two dozen cameras.

They released what they believe is the first video footage of wolves gobbling blueberries.

Other wolf researchers have been impressed by the discoveries and credit Gable and Homkes for the effort they put into it.

“What they’re finding is so novel in so many ways that it really is opening up so many other questions,” said Shannon Barber-Meyer, who has studied wolves and is a research wildlife biologist with the U.S. Geological Survey. “They really put in so much effort to find out things that the rest of us knew were hard to do.”

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