Biologists from the University of California, Berkeley have observed gray wolves near Yellowstone National Park traveling distances of 20 kilometers or more across difficult terrain with very young pups. This behavior was documented through camera trap photos and GPS tracking.

“The first time I saw a camera trap photo of a wolf carrying its pup, I just cracked up because the pup is being carried by its butt,” said Avery Shawler, first author of a new study published in Current Biology. “You can picture a squirming child and the mom just being like, ‘All right, we’re doing this.’”

The research focused on wolves that track the Cody Herd on the southeast side of Yellowstone National Park. According to Shawler and colleagues, these journeys appear to be an effort by wolf packs to move closer to elk during their spring migration to higher elevations. The study marks the first observation outside the Arctic of gray wolves migrating or shifting their territorial range during pup-rearing season in response to prey movements.

“Our findings counter years of assumptions by researchers that migratory hoofed mammals can escape predation in spring because [their predators] are tied to dens and immobile offspring,” said Arthur Middleton, senior author and professor at UC Berkeley.

Understanding these adaptations is important for conservation efforts involving both species. Shawler noted that many wolves live outside protected areas where they may come into contact with livestock. She explained, “In the U.S., more wolves live outside of protected areas than within protected areas, and these wolves are going to overlap with humans and livestock. Our research provides some insight into the behavior of wolves living on working landscapes and how they’ve had to adapt to an environment that is different from what wolves were dealing with 100 years ago.”

Gray wolves were reintroduced into Yellowstone National Park in 1995; their population in the Greater Yellowstone Ecosystem has grown to around 500 since then. The region also supports tens of thousands of partially migratory elk.

Climate change and land use changes are affecting both elk and wolf populations in Yellowstone. Earlier studies led by Middleton found that elk now arrive at winter ranges much later than they did two decades ago due to shifts in migration timing.

To better understand how these changing patterns affect predator-prey interactions, researchers tracked 19 gray wolves and 99 elk using GPS collars between 2019 and 2021.

They discovered differences among wolf packs depending on which elk herds they followed. Packs tracking short-distance migrating herds generally stayed near their original dens while those following long-distance herds engaged in what researchers described as “commuting” — temporary trips outside their home territory — or “migrating,” where entire packs relocated up to 50 kilometers away for new seasonal ranges. Sometimes adults carried pups as far as 20 kilometers from original den sites.

“In Yellowstone, research has shown how a lot of wolf mortality can come from other packs coming in and killing pups, because there’s a lot of packs competing for space and food,” Shawler said. “It’s pretty wild that this risky behavior of moving young pups is even occurring when that’s happening next door.”

The study's findings may inform management practices beyond Wyoming; California now has about ten wolf packs after recolonization began there in 2011. Middleton is co-leading the California Wolf Project, which aims to study factors influencing wolf populations statewide.

“While it’s still early days, our partners in California have a strong hunch that the numbers and movements of deer and elk are playing into wolf behavior, including livestock predation,” Middleton said. “The work around Yellowstone sharpens our ideas and approaches as we grow the project in California.”

Co-authors include Kristin J. Barker (UC Berkeley), Wenjing Xu (Senckenberg Biodiversity & Climate Research Centre), Kenneth J. Mills (Wyoming Game & Fish Department), Tony W. Mong (Wyoming Game & Fish Department). The study received support from several organizations including UC Berkeley.