Concerns over deer and other animal populations have inspired a series of predator-prey studies in Washington
Stealthy survey: Wolves are thriving. Researchers want to know how their prey are doing. Photo: ODFW.
By K.C. Mehaffey. January 5, 2023. Scientists are beginning to untangle the complex food web involving Washington’s deer, elk and moose populations and their predators—including wolves, cougars, bears, coyotes, bobcats and humans.
A major five-year joint research project conducted by the Washington Department of Fish and Wildlife and the University of Washington is producing numerous peer-reviewed studies that will be pulled together in a report to the state legislature this spring.
Donny Martorello, science division manager for WDFW’s Wildlife Program, said that after wrapping up their field work last year, UW students have been working on graduate dissertations and peer-reviewed studies, which are now being published.
“Once all that is done by mid-spring, then we’ll have the exciting opportunity to sit down and say, ‘What does it all mean?” he told the Washington Fish and Wildlife Commission on Dec. 9.
He said the state agency will be considering whether the studies are able to answer questions about the impact of wolves, and can be used in management decisions.
Through the Predator-Prey Project, scientists put radio collars on the predators and their prey in two parts of Washington—the northeast corner, where wolves have become commonplace, and the north central part of the state, where wolves are still repopulating the area.
Students and biologists collected and analyzed data from 660 GPS-collared animals, 2,500 scats and 350 wildlife cameras from 2016 through 2021. They investigated more than 600 sites where deer and elk died, set up 150 cameras at kill sites to see who returned, and surveyed vegetation to analyze the quality of habitat at 260 sites.
Studies prompted by concerns
The research was initiated largely by hunters and conservationists who worried that the deer and elk populations may not withstand the added stress from a growing population of wolves, especially in northeastern Washington, where 22 of the state’s 33 packs now reside.
In 2015, lawmakers from that region heeded their constituents’ concerns and proposed a bill directing WDFW and UW to study the impact that wolves are having on the state’s ungulate species.
Sen. Shelly Short, R-Addy, was a state representative at the time and the prime sponsor of a bill to study the wolves’ impact.
She said although it never passed the legislature, the bill led to a budget provision in 2016 to fund the project.
Where the wolves are: Wolf packs in Washington. Map: UW School of Environmental and Forest Sciences
Short said she pushed for the law because wolves—absent for 80 years—moved back into the state and were growing in number every year.
According to the state’s most recent annual report on wolves, there were at least 206 wolves in Washington in 2021, and the population had grown by an average of 25% each year since first reappearing in 2008.
“We have this high apex predator back in our environment. So, how are other predators responding? And are there enough ungulates? That was always the basis” of the joint research project, said Short.
Shifting dynamics
The Predator-Prey Project is beginning to answer those questions—and many more—but the answers won’t be simple.
UW graduate student Taylor Ganz is attempting to figure out how wolves are impacting deer and elk for her doctorate dissertation.
She told commissioners that white-tailed deer and elk populations in the northeast corner of the state were not experiencing dramatic declines during the five-year study period, according to her modeling.
Hunting the hunters: Taylor Ganz. Photo: Prugh Lab
She explained that scientists don’t have numerical population estimates for deer and elk because they’re too hard to count, but she used data gathered through the project to assess changes in population.
Within the study area—which includes the territories of four wolf packs—the deer population seemed to be declining slightly, while the elk population was growing, she said.
Ganz cautioned, however, that numerous factors contribute to population growth, and noted the data for her study was gathered before an outbreak of hemorrhagic disease in the white-tailed deer population.
“This is a really complex system with a lot of dynamics going on,” Ganz said. “We did our very best to investigate as many of those as possible, but we definitely don’t have all the answers.”
Ganz said that when there are population declines, it’s not usually caused by one factor. Deer in northeastern Washington experience severe winters, limitations in forage and a group of predators whose populations are also changing.
“The population dynamics from that five-year period that we studied doesn’t indicate that there’s anything concerning” about the slightly declining deer population, which is within normal parameters of fluctuation, she added.
Forensic research
Ganz is focusing on the northeast ungulates and what factors influence their mortality, seeking to answer how wolves, other predators, forage availability and changes in the landscape affect their survival and movement.
That required an analysis of why each collared animal died.
Ganz said some causes of death—like being hit by a vehicle—may be relatively easy to confirm. But investigating a predator kill is more complex.
“We investigate the scene as rapidly as possible, basically playing CSI (Crime Scene Investigation) to try and figure out what happened,” she said.
Biologists mostly use bite wounds to confirm that an animal died of predation.
“As you can imagine it can be really hard to find this information, so there are many cases where we have an unknown cause of death, or were unable to confirm that an animal died of predation even though that may likely be the case,” Ganz said.
Tracks at the scene and patterns of consumption offer clues, but scavengers complicate their findings, Ganz noted.
Down not out: A Tucannon Pack wolf in Washington wakes up from immobilizing drugs after capture. Photo: WDFW
To help, scientists also collected DNA samples.
Ganz said that, surprisingly, of 46 adult female deer and 72 fawn mortalities in the northeast study area, none were confirmed to be killed by wolves.
“Now, we know from diet analyses that wolves are eating deer in this system, but because wolves very quickly consume a carcass, and disperse it, it can be very hard to confirm,” she said.
Some wolf kills were likely among the unknown causes.
Of the confirmed or unconfirmed-but-likely predations, cougars were found to be the largest predator of adult white-tailed deer. For fawns, cougars, coyotes and bobcats were the major confirmed predators.
Getting hit by a vehicle was also high on the list of confirmed fatalities.
Converging studies
Ganz’s study on ungulate mortality is just one of many coming out of the Predator-Prey Project.
Other scientists used the data to look at things such as the interactions between wolves and cougars, and the impacts of human activities—such as hunting and cattle grazing—on these wildlife species.
Beth Gardner, associate professor at the UW School of Environmental and Forest Sciences and director of its Quantitative Ecology Lab, was one of three principal investigators for the project.
Den master: Beth Gardner. Photo: UW School of Environmental and Forest Sciences
She said in addition to the primary graduate students conducting the research, dozens of other graduate and undergraduate students helped, both in the field and by analyzing data.
WDFW biologists led efforts to capture and collar the animals, and gathered some of the data while students were in school. Several studies are complete, but the peer-review process is ongoing, Gardner said, noting, “We will still have a fair number of products that will come out later.”
Undergraduate students also used the data to develop capstone projects, she said. Topics included examining the effects of hunting on deer productivity; whether black bears use habitat where livestock are grazed; and the impact of wolves on coyote populations.
“It’s really touched a lot of students,” Gardner said, noting that one student recently decided to use the data that’s already been gathered to look into impacts of smoke on wildlife.
But figuring out the impact wolves are having on the state’s deer and elk populations is still the central theme of the project.
Gardner said a lot of people told the researchers that there used to be a lot more deer, but it’s hard to separate out impacts caused by wolves or by other changes—like human population growth.
“It’s going to be an ongoing question, and it’s going to require reevaluation. Now, we have a good snapshot in their recolonization period,” she said.
Landmark report landing soon
While Short is still awaiting the report, she’s encouraged by the quality of work coming out of the project.
“As with all research, it’s never a one-and-done,” she said. “It’s very clear they thought about how they went about getting samples, and how thoroughly things were tested. I think it will provide a good piece of information.”
Short said the research is also raising new questions for her—like whether the 36% annual survival rate for white-tailed fawns noted in Ganz’s study is unusual.
The lawmaker said while the number of wolves in the state’s northeast corner continues to grow, most people—including ranchers—have accepted their presence, as long as the state continues to manage them.
This project could help them do that, she said.
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