New research shows that the effects of wolves on the recovery of aspen has been exaggerated by how it was measured

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S.J. & JESSIE E. QUINNEY COLLEGE OF NATURAL RESOURCES, UTAH STATE UNIVERSITY

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IMAGE: PREVIOUS RESEARCH SHOWED STRONG POSITIVE GROWTH IN YOUNG ASPENS IN YELLOWSTONE NATIONAL PARK AS THE ELK POPULATIONS DECREASED—A WELCOME RESULT. BUT NEW RESEARCH SHOWS ASPEN RECOVERY IS NOT AS ROBUST AS PREVIOUSLY THOUGHT. view more 

CREDIT: PHOTO COURTESY LAINIE BRICE

It’s an environmental success story that feels like a parable—the reintroduction of wolves in Yellowstone National Park in the mid-1990s triggered a cascade of effects that ultimately restored the ecosystem, including the recovery of aspen trees. But like many stories based on ecological realities, it’s more complex than at first glance—aspen recovery in the park is not as robust as generally believed, according to new research.

The Yellowstone story is a textbook example of a trophic cascade, in which predators help plants grow by eating or scaring away herbivores that eat the plants. When wolves were reintroduced into the Yellowstone food chain, they helped to reduce numbers of elk, which had been consuming young aspen trees. Previous research showed strong positive growth in young aspen as the elk populations decreased—a welcome result, as aspen forests have been vanishing from the northern Yellowstone landscape for the last century.

But new research from Elaine Brice and Dan MacNulty, from Utah State University’sDepartment of Wildland Resources and Ecology Center, and Eric Larsen, from the University of Wisconsin Stevens Point’s Department of Geography and Geology, shows that the effect of wolves on the recovery of aspen has been exaggerated by how it was measured.

Previous studies evaluated aspen recovery in Yellowstone by measuring the five tallest young aspen within a stand. The reasoning was that the tallest young aspen trees represent a ‘leading edge’ indicator of the future recovery of the entire aspen population. But this is not the case—sampling only the tallest young aspen estimated a rate of recovery that was significantly faster than was estimated by random sampling of all young aspen within the stand, according to the research.

“These are extremely complex systems, and understanding them is a major challenge because they are difficult to properly sample,” said Brice. “The traditional method of sampling by only using the tallest young aspen plants to measure growth—which most research currently relies on—doesn’t capture the entire picture.”

For one, elk are picky about the aspen they consume. They tend to eat plants at shoulder height for which they don’t have to crane their necks. As the leader stem (main trunk) of a young aspen grows past the shoulder height of adult elk, it is decreasingly likely to be eaten as it grows taller, said MacNulty. “This means that the tallest young aspen grow faster because they are taller, not because wolves reduce elk browsing,” said MacNulty. This finding highlights the complicating fact that height of young aspen is both a cause and an effect of reduced elk browsing. 

Taller aspen also thrive because they tend to have the best growing conditions (sunlight, moisture, soil quality). Measuring just the tallest young trees downplays the role of these other factors that have nothing to do with elk or wolf populations. And measuring just the tallest aspen also overlooks the failure of some young aspen to regenerate in the first place.

“That’s like calculating a team’s batting average without the player who always strikes out,” said Brice. Random sampling from the research showed an absence of aspen regeneration in some places, a vital piece missing from the initial measurements.

Understanding how ecosystems respond to changes in large predator populations is vital to resolving broader debates about the structure of food webs, determining species abundance and delivering ecosystem services, said the authors. This study demonstrates how deviations from basic sampling principles can distort this understanding. Non-random sampling overestimated the strength of a trophic cascade in this case, but it may underestimate cascading effects in other situations. Randomization is one of the few protections against unreliable inferences and the misguided management decisions they may inspire, they said.

“The bottom line is that ecologists must stick to classic principles of sampling design, like randomization, to fully understand trophic cascades in complex wildlife systems like Yellowstone,” said MacNulty.

Carnivore interactions are a game of risk and reward

 Coyotes can eat by scavenging cougars' prey but it's a risky proposition as coyotes often end up killed by cougars too, a new study of predator interactions by Oregon State University shows.

Researchers in the OSU College of Agricultural Sciences also looked at black bears and bobcats and found the interplay within the four-species "guild" of predators defied simplistic description.

Findings, published today in the Proceedings of the National Academy of Sciences, challenge the traditional model for carnivore interactions among species: that dominant predators suppress the other ones.

The study, one of the first to quantify rates of both scavenging and intraguild predation, is important because understanding the influence of dominant predators is necessary for anticipating the ecological effects of changes in carnivore populations.

Factoring in the study area's cougar and coyote density, the findings suggest nearly one-quarter of the area's coyote population is killed by cougars each year, although in many cases, coyotes did not appear to be killed while scavenging.

"That kill percentage estimate implies a strong suppressive effect counteracting the benefit to coyotes provided by the cougars," said Oregon State Ph.D. student Joel Ruprecht. "Overall, the issue of whether subordinate species incur a net fitness cost or benefit from dominant predators is far from resolved."

Coyotes seem to readily accept the risk of being near a cougar if a food reward is available, possibly because they can manage the risk by being extra vigilant, he added. Also, if a dominant predator becomes satiated after feeding on a kill, it may not be motivated to kill other carnivores.

"Learning whether dominant carnivores kill subordinate carnivores for food or for the long-term benefit of removing a competitor needs to be the focus of further research," said OSU associate professor Taal Levi.

Ruprecht, Levi and Ph.D. student Charlotte Eriksson led the study, which also involved scientists from the Oregon Department of Fish and Wildlife, the U.S. Forest Service and the University of California, Santa Cruz.

Between 2016 and 2020 in the Blue Mountains of northeastern Oregon, researchers tagged a "guild" of predators -- 17 cougars, 17 coyotes, 11 black bears and six bobcats -- with GPS collars that recorded their location every few hours. Scientists also tested the animals' scat to see what they were eating.

"How often elk turns up in the scats of the subordinate predators is a proxy for how much scavenging they're doing because it's unlikely any of them are killing adult elk," Levi said. "That means if they're eating elk it's probably either via scavenging or preying on calves, but in the Blue Mountains coyotes and bobcats rarely kill elk calves; black bears are somewhat more likely to."

To further zero in on what the predators were eating, the scientists did ground searches based on clusters of cougar GPS locations -- indicating potential kills -- and set up cameras at 28 of the 128 confirmed kill sites. The cameras allowed for a daily tally of site visits by bears, bobcats and coyotes and thus enabled an estimate of scavenging rates.

"The traditional paradigm for species interactions among carnivores has stressed hierarchies: Dominant predators curb the efforts of the next level, the mesopredators," Levi said. "We found evidence of that but also evidence of facilitation. The coyotes we studied had a strong attraction to kill sites, frequent carrion in their diet and high scavenging rates, compared to two indicators of suppression: They avoided cougars and also were preyed on by them."

There was no evidence to suggest coyotes' attraction to kill sites was lessened if a cougar was around, he added, indicating coyotes' willingness to disregard cougar risk if a food reward was present.

Bears had moderate scavenging rates and ate moderate levels of carrion but showed a statistically significant aversion to being around cougars. Nothing suggested bears were particularly attracted to kill sites or suffered predation at the hands of cougars, or that cougars had any effect at all on bobcats.

"Bobcats were indifferent to both cougars and their kill sites," Ruprecht said. "And bobcats weren't avoiding coyotes in general, meaning coyote presence was probably not a primary reason bobcats didn't feed on cougar kills."

There were coyotes on the scene at 89% of carcasses, bears at 50% of carcasses outside the hibernation period and bobcats at none of them.

Scat analyses showed elk in 58% of coyote scats and deer in 12%, comparable to the percentages for cougar scats (61% and 22%). Bear scats contained elk 29% of the time and deer 8% of the time. No bobcat scats provided evidence they had eaten elk, and 8% of bobcat scats contained deer.

"Investigations of the cougar kill sites showed that elk represented 64% and deer 16% of the prey items killed by cougars," Levi said. "Investigations also showed that coyotes represented 7% of cougar kills. In eight cases coyotes were the only prey item found, and in one case a dead coyote was found along with another prey item."

The bobcat findings were particularly surprising, he noted, because bobcats are known to scavenge from and be eaten by cougars in other locations, and also because it's usually more likely for a wild cat like a cougar to kill another species of cat than a predator from outside their taxonomic family.

"By foregoing the energy benefits they could gain from eating on cougar kills, and in doing so reducing mortality risk, bobcats in our study area approached the risk-reward tradeoff quite differently than the coyotes," he said. "But scavenging is only optimal under a specific set of conditions that also includes the probability of finding other food sources, and the energy required to search for them. The coyotes we studied faced little risk except from cougars and scavenged profusely; they're probably less likely to scavenge when there are lots of competitors for each carcass."

Southeast’s gray foxes may be struggling for survival

Competition for food from coyotes seems to be key to declining populations

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UNIVERSITY OF GEORGIA

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IMAGE: GRAY FOX POPULATIONS SEEM TO BE DECLINING IN THE SOUTHEAST, ACCORDING TO UNIVERSITY OF GEORGIA RESEARCH. view more 

CREDIT: SARAH WEBSTER

For generations, gray foxes have been part of the Southeastern landscape. They, along with red foxes, are among the carnivores that dine on a range of smaller animals, plants and berries.

But a new study published by researchers from the University of Georgia suggests competition for food from coyotes—a relative newcomer to the Southeast—may be putting pressure on foxes, particularly the gray fox.

“Gray fox populations, especially in the Southeast, seem to be declining, and have been for some decades,” said James Beasley, an associate professor in the UGA Warnell School of Forestry and Natural Resources whose doctoral student, Sarah Webster, wrote the study as part of her dissertation.

The study, published in the Journal of Mammology, was co-authored by Beasley as well as Warnell professor Michael Chamberlain and Warnell alumnus Joseph Hinton.

By looking at reports given by licensed animal trappers in South Carolina, where Beasley’s lab is located, it was clear to the researchers that the number of harvested foxes—particularly gray foxes—has been decreasing, while the number of harvested coyotes has increased.

“Here on the Savannah River Site, there are excellent historical trapping records and gray foxes used to be really abundant,” said Beasley. “But now we don’t see them nearly as frequently. That’s prompted questions of why—why are we seeing the reduction in these numbers?”

At the Savannah River Ecology Lab in Aiken, South Carolina, where the study took place, Beasley said habitats have changed dramatically over the years, from agricultural areas preferred by red foxes to forested areas more conducive to tree-climbing gray foxes. Also, food is abundant for generalist carnivores such as coyotes and foxes, which will eat a variety of plants and animals, and coyotes are now abundant in this landscape.

In the Midwest, where foxes and coyotes have lived together for hundreds of years, the species have found a way to carve out food sources without overlapping too much—scientists call this “partitioning.” But coyotes have only been in the Southeast since the 1970s, giving them far less time to sort out their overlapping food preferences.

Still, Webster wanted more information about how coyotes’ and foxes’ food sources might differ between the regions. So, she used hair samples gathered from red and gray foxes and coyotes from both regions and from a variety of decades, including preserved samples from the Georgia Museum of Natural History. By measuring the amounts of carbon or nitrogen in the hair, Webster was able to assess the amount of overlap in diet between each species.

For example, a diet high in protein would manifest as a higher nitrogen content. Vegetation, such as fruits or grasses, translates as carbon in the hair samples. By noting the relative amounts of carbon and nitrogen content in hair samples, Webster was able to assemble a picture of how much diet overlap there was between each species in each region.

The results? There are significant regional differences in how coyotes and foxes dine.

“In the Midwest, we found there were significant differences in diet between species, whereas in the Southeast they overlapped significantly,” she said. In the Southeast, red and gray foxes had a large amount of overlap in their diets prior to the onset of coyotes, and that overlapping continued once coyotes arrived, according to more recent samples. “So, all three species are overlapping now in the Southeast.”

Beasley noted that the diet partitioning that takes place among these species in the Midwest is something that developed over hundreds of years, as coyotes and foxes learned to navigate the landscape around each other. There apparently hasn’t been enough time for that dynamic to play out in the Southeast.

“The question is, will that happen fast enough, before the gray fox populations continue to decline further?” he added. “It’s not exceptionally dire for the gray fox, but we now often find them closer to buildings or other marginalized areas. So, they may be finding other mechanisms to coexist with coyotes. But they do need forested areas.”

Habitat is one way, said Webster, that we can work to ensure future populations of gray foxes remain stable. When we understand the dynamics at play between the species, we can better plan for the future.

“We don’t have good evidence that we can effectively manage coyote populations on a large scale. They’re generalists, and they’re too flexible in their behavior and patterns. They will survive just fine,” said Webster. “So, a more effective approach likely would be to focus on the gray fox. Step one is to better understand how the gray fox population is doing by studying their population dynamics, and then going forward from there and trying to build effective management around the gray fox to ensure they continue to thrive in the Southeast.”

DNA assay aids in identifying and protecting North American wolves, coyotes

NORTH CAROLINA STATE UNIVERSITY

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Forensics specialists can use a commercial assay targeting mitochondrial DNA to accurately discriminate between wolf, coyote and dog species, according to a new study from North Carolina State University. The genetic information can be obtained from smaller or more degraded samples, and could aid authorities in prosecuting hunting jurisdiction violations and preserving protected species.

In the U.S., certain wolf subspecies or species are endangered and restricted in terms of hunting status. It is also illegal to deliberately breed wolves or coyotes with domesticated dogs.

"If it's a case where you have a whole specimen, authorities can typically identify it based on physical characteristics, though similarity between some species makes that method less than ideal," says Kelly Meiklejohn, assistant professor of forensic science at NC State and corresponding author of the research. "If you're working with cross-bred animals, or incomplete specimens, you need DNA-based methods to accurately determine what species you have."

Although some U.S. federal laboratories perform DNA-based identification of wolves and coyotes, their methods and genetic reference databases aren't publicly available. Meiklejohn partnered with the U.S. Fish and Wildlife Service to see if it was possible to use a commercially available assay designed for dogs as a way to recover the mitochondrial genome from diverse North American canid species.

The mitochondrial genome is one of two genomes inherited from an animal's parents. Specifically, the mitochondrial genome is inherited from the mother. It is useful for species identification both because its circular shape makes it less prone to degradation, and because there are more copies of this genome per cell, increasing the chance of retrieving useful material from small or damaged samples.

The team used a method, called a 'hybridization capture,' in which about 80 base-pair long RNA fragments are used to isolate DNA for sequencing. Samples are incubated with the RNA fragments, and if there's a match, the fragment will bind with the sample's DNA. The bound DNA can be isolated and sequenced. In this case, the team used a hybridization capture panel designed for the dog mitochondrial genome.

"The fragments will bind if there is about 80% similarity, which is why we felt the dog kit would be useful for sequencing wolves and coyotes," Meiklejohn says. "Dogs only diverged from wolves around 20,000 years ago, so the mitochondrial genomes aren't that different."

They sequenced 51 samples, and were able to recover full mitochondrial genomes and successfully differentiate between four species of interest: dog, wolf, Mexican wolf, and coyote.

"Essentially, this finding means we can do more with less," Meiklejohn says. "In forensics we rarely have high quality DNA samples; they've usually been exposed to the environment and are degraded. The flexibility of this kit allows us to determine the species we're looking at, which in turn may aid in prosecuting hunting or breeding violations and protecting endangered canid species."

Environmentalists plan to file lawsuit over Idaho's new wolf law

 

 

Environmental groups have notified Idaho Gov. Brad Little and other state officials of their intent to file a lawsuit over an expanded wolf-killing law the groups say will result in the illegal killing of federally protected grizzly bear and lynx

 Environmental groups have notified Idaho Gov. Brad Little and other state officials of their intent to file a lawsuit over an expanded wolf-killing law they believe will result in the illegal killing of federally protected grizzly bear and lynx.

The Center for Biological Diversity, Western Watersheds Project and others on Monday gave a required 60-day notice of their intent to sue if Idaho officials don’t prohibit all hunting, trapping and snaring in grizzly bear and lynx habitat.

For lynx, the conditions could cover most of Idaho except for the southwestern portion of the state. For grizzly bears, the areas would include portions of northern, central and eastern Idaho. Wolves are found in roughly the northern two-thirds of the state.

In May, the Republican governor signed into law a measure lawmakers said could lead to killing 90% of the state’s 1,500 wolves through expanded trapping and hunting. It took effect July 1. Lawmakers who sponsored the measure, backed by hunters and the state’s ranching sector but heavily criticized by environmental advocates, said numerous times that the state is allowed to cut the number of wolves down to 150 before federal authorities would take over management of the species. They said reducing the wolf population would reduce attacks on livestock and boost deer and elk herds.

“Lynx, grizzly bears, and gray wolves all inhabit similar habitat types and geographic ranges in Idaho, and wolf hunting and trapping therefore frequently occur in areas in which lynx and grizzlies are also present,” the groups said in their letter. “Moreover, because snare and other authorized means of hunting and trapping are imprecise tools, they pose a substantial risk to non-target species, including lynx and grizzly bears.”

Besides Little, the letter was also sent to the members of the Idaho Fish and Game Commission and the directors of the Idaho Department of Fish and Game and Idaho State Department of Agriculture.

Roger Phillips, spokesman for the state Department of Fish and Game, said the agency doesn’t comment on pending litigation.

Little’s office didn’t immediately respond to a request for comment from The Associated Press.

Environmental groups filed a similar notice of intent to sue in Montana last month that also involves the potential killing of grizzly bears and lynx by wolf hunters and trappers.

A primary change in the new law allows the state to hire private contractors to kill wolves and provides more money for state officials to hire the contractors.

The law also expands the way wolves can be hunted and killed.

It’s not clear if the expanded methods and seasons to kill wolves would reduce the wolf population to 150. Republican state Rep. Fred Wood, a former member of the Idaho Fish and Game Commission, said the only way to do that would be to use poison, which is not in the new law.

However, hunters have said night-vision scopes, now allowed, could significantly increase the number of wolves killed. But the threatened lawsuit cites possible deaths of grizzly bears and lynx from expanded trapping and snaring of wolves.

“Idaho’s outdated plans for wolf killing will inevitably harm other native wildlife species,” said Patrick Kelly, Idaho director of Western Watersheds Project. “It’s unacceptable to allow imperiled species to be ‘collateral damage’ in Idaho’s war on wolves.”

The state Department of Fish and Game reported in February that the wolf population has held at about 1,500 the past two years. The numbers were derived by using remote cameras and other methods.

About 500 wolves have been killed in the state in each of the last two years by hunters, trappers and wolf control measures carried out by state and federal authorities.

Idaho Cattle Association Executive Vice President Cameron Mulrony told Capital Press the new law provides needed additional tools to control wolves, and “will get the ball rolling.”

The statute could be amended and administrative rules revised, both with legislative approval, later if necessary, he said.

Wolf pups born on Isle Royale, moose poised for decline

MICHIGAN TECHNOLOGICAL UNIVERSITY

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IMAGE: IN THIS IMAGE FROM APRIL 2021, AN EMACIATED AND NUTRITIONALLY STRESSED BULL MOOSE -- WHO IS ALSO SEVERELY IMPACTED BY WINTER TICKS -- BEDS DOWN ON THE ISLAND.view more 

CREDIT: MICHIGAN TECH

The COVID-19 pandemic halted the in-person wintertime survey of wolves and moose on the island for the first time in 63 years. Consequently, there are no estimates of wolf or moose abundance for 2021, and the next estimates are scheduled in February 2022. But though the Isle Royale Winter Study didn't happen quite as planned, researchers were still able to visit the remote national park in the spring.

Now, fieldwork has resumed and Michigan Technological University researchers have already uncovered new information about these two iconic wildlife populations. In particular, wolves produced at least two litters of pups, and moose appear poised for decline.

In the Isle Royale Winter Study, Michigan Tech researchers share other significant developments about curating the world's largest moose bone collection, advances in understanding of wolf foraging behavior and the nutritional health of the moose population.

Key points:

• The Isle Royale wolf population is likely growing. "We recovered footage of a group of four wolf pups taken in January 2021 by remote cameras at the east end of Isle Royale," said Sarah Hoy, research assistant professor in Michigan Tech's College of Forest Resources and Environmental Science (CFRES). "Additionally, observations of tracks and scats left by wolf pups last fall at two different locations suggest that there were probably two different litters of pups living at the east end of the island in September 2020."

• Wolves are specialized foragers. "Wolf foraging behavior seems driven by minimizing the risks associated with killing large prey, like moose, even when the differences in vulnerability among individual moose might seem relatively subtle compared to when predators are choosing between different prey species," Hoy said.

• Nutritional stress stacks the deck against moose, which holds significant implications for how moose will handle a warming climate. "We found that the nutritional health of moose was importantly influenced by how hot it is during the summer, and also by how deep the snow is in winter," Hoy said. "Moose tended to be more nutritionally stressed during winters with deep snow, which may be because deeper snow makes it more difficult for moose to move around and find food."

• The moose population is likely declining. "Moose really struggled to find enough food this past winter," Hoy said. "Because there have been such large numbers of moose on the island over the last five years and moose ate branches faster than the trees can recover and replace them, the amount of food available to moose during winter has been getting progressively worse each year since 2017.

• Winter ticks are worse than usual this year, as evidenced by moose with very little fur left in spring -- having scratched or bitten off almost all of their winter coats in an effort to rid themselves of the blood-sucking parasites. This is significant because blood loss to ticks can exacerbate the detrimental effects of food shortage. Despite the mild winter, depleted food supplies and ticks made life harder for the island's moose this year.

Hunting and hidden deaths led to 30% reduction in WI wolf population

UNIVERSITY OF WISCONSIN-MADISON

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MADISON, Wis. -- About 100 additional wolves died over the winter in Wisconsin as a result of the delisting of grey wolves under the Endangered Species Act, alongside the 218 wolves killed by licensed hunters during Wisconsin's first public wolf hunt, according to new research.

The combined loss of 313 to 323 wolves represents a decline in the state's wolf population of between 27% and 33% between April 2020 and April 2021. Researchers estimate that a majority of these additional, uncounted deaths are due to something called cryptic poaching, where poachers hide evidence of illegal killings.

The findings are the first estimate of Wisconsin's wolf population since the public hunt in February, which ended early after hunters exceeded the quota of 119 wolves within a few days. These population estimates can help the Wisconsin Department of Natural Resources (DNR) prepare for the next legally mandated wolf hunt this fall.

They also provide guidance to other states planning wolf hunts following the removal of federal protections announced in November 2020 and effective January 2021.

University of Wisconsin-Madison environmental studies scientists Adrian Treves, Francisco Santiago-Ávila and Karann Putrevu performed the research, which was published July 5 in the journal PeerJ.

Under a variety of population growth scenarios, the researchers estimate that Wisconsin now hosts between 695 and 751 wolves, compared with at least 1,034 wolves last year. The scientists say this likely represents the maximum current wolf population, because they incorporated optimistic assumptions about population growth and low poaching rates into their models.

This decline is despite the hunting quota of 119 wolves for non-native hunters, set with the goal of helping maintain but not reduce the state's wolf population. Ojibwe Tribes were granted a quota of 81 wolves, but they did not conduct a hunt.

"Although the DNR is aiming for a stable population, we estimate the population actually dropped significantly," says Treves, a professor in the Nelson Institute for Environmental Studies and director of the Carnivore Coexistence Lab at UW-Madison.

The new study suggests that about one-third of the population decline is due to hidden deaths in the wolf population, resulting from relaxed legal protections.

Previous research by the Treves lab showed that wolf population growth declined in Wisconsin and Michigan when legal protections were relaxed, regardless of the number of wolves legally killed. And Santiago-Ávila led research that found that Wisconsin's wolves and the heavily monitored Mexican wolves of the American Southwest disappeared at greater rates when lethal control methods were allowed.

Other studies by the lab of attitudes toward wolves suggest that when governments allow lethal management, would-be poachers are inclined to kill more wolves because the relaxed policies signal that predators are less valued.

Those previous findings helped Santiago-Ávila, Putrevu and Treves model the uncounted deaths in Wisconsin since last November.

"During these periods, we see an effect on poaching, both reported and cryptic. Those wolves disappear and you never find them again," says Santiago-Ávila, a postdoctoral researcher in the lab. "Additional deaths are caused simply by the policy signal, and the wolf hunt adds to that."

Treves and his team estimate that the population could recover in one to two years without hunting. Wisconsin law requires a wolf hunt between November and February when hunting is not prohibited by federal protections.

Following the federal delisting of wolves that became effective in January 2021, the DNR initially planned to conduct the first hunt in November 2021. But after a lawsuit, the DNR immediately implemented a wolf hunt at the end of February.

The research team hopes that the Wisconsin DNR and other states' natural resource agencies take advantage of their methods to develop a more complete assessment of the effect of new policies on predator populations.

"These methods and models are freely available to these agencies," says Putrevu, a doctoral student who also researches tiger populations in the Russian Far East. "They should take advantage of the best available science to meet their stated goals."