Gray wolves carry young pups over rugged terrain to track spring elk migration

Gray wolf pups are born nearly helpless: blind, deaf and lacking the acute sense of smell of their elders. They usually remain in the safe confines of their den until they are at least three weeks old.

That is why UC Berkeley biologists were surprised to observe gray wolves near Yellowstone National Park traveling 20 kilometers or more over rugged, mountainous terrain, with very young pups in tow.

“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 presenting the findings, which appeared online today (Aug. 1) in the journal Current Biology. “You can picture a squirming child and the mom just being like, ‘All right, we’re doing this.'”

Shawler and the other researchers believe wolves undertook these risky journeys to move their packs closer to elk, their preferred prey, during the elk spring migration to higher altitudes. The study is the first time gray wolves outside of the Arctic have been observed migrating, or shifting their territorial range, to be closer to prey during pup-rearing season.

“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 study senior author Arthur Middleton, a Berkeley professor of environmental science, policy and management.

Understanding how wolves are adapting to the movements of their prey is key to the conservation of both species, Shawler said. It can help land managers understand seasonal patterns of human-wildlife conflict in an ecosystem that includes both ranches and wilderness, where wolves may view livestock as a tasty alternative to elk.

“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,” said Shawler, who completed a Ph.D. at UC Berkeley in 2024. “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 to Yellowstone National Park in 1995, and researchers estimate that their population in the Greater Yellowstone Ecosystem has since grown to around 500. Tens of thousands of partially migratory elk also inhabit the region.

Climate change and shifts in land use are putting pressure on both species and leading them to adapt accordingly. Earlier research led by Middleton showed that the timing of annual elk migrations is currently in flux, with elk arriving at their winter ranges up to 50 days later in 2015 compared to 2001.

To explore how elk migration patterns impact wolf behavior, the researchers used GPS collars to track the movements of 19 gray wolves and 99 elk in the eastern Greater Yellowstone Ecosystem between 2019 and 2021.

They found that wolves are surprisingly adaptable to the movements of their prey. Some elk herds in Yellowstone only migrate short distances in the spring, and the wolf packs that tracked them generally stayed in the same territory where they first established their dens. Other elk herds travel much longer distances in the spring, and wolf packs that tracked them had to get more creative, engaging in behaviors the researchers called “commuting” and “migrating.”

The researchers used the term “commuting” to describe temporary forays taken outside of the wolves’ home territories, usually to track migrating elk herds.

Wolves “migrated” when they moved to an entirely new seasonal range, following migrating elk up to 50 kilometers. Sometimes they carried small pups as far as 20 kilometers from their original dens to new pack “rendezvous” 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 findings can inform conservation efforts and land management in any region that has gray wolves—including California, which is home to approximately 10 packs after wolves began recolonizing the state in 2011. Middleton is co-leading the new California Wolf Project, which aims to understand the social and ecological factors that are shaping these wolf populations.

“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.”

Additional study co-authors include Kristin J. Barker of UC Berkeley and Beyond Yellowstone Living Lab; Wenjing Xu of the Senckenberg Biodiversity and Climate Research Center in Germany; and Kenneth J. Mills and Tony W. Mong of the Wyoming Game and Fish Department.