Wolf reintroduction: Yellowstone's 'landscape of fear' not so scary after all

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Utah State University scientists have shown that a 'landscape of fear' does not keep Yellowstone elk from using risky habitats where wolves kill them. In an Early View online article of Ecological Monographs, the researchers discuss how elk use nightly lulls in wolf activity to safely access dangerous areas.

Credit: Chad Wildermuth

After wolves were reintroduced to Yellowstone National Park in the mid-1990s, some scientists thought the large predator reestablished a 'landscape of fear' that caused elk, the wolf's main prey, to avoid risky places where wolves killed them. This fueled the emerging idea that predators affect prey populations and ecosystems not only by eating prey animals, but by scaring them too. But according to findings from Utah State University ecologists Michel Kohl and Dan MacNulty, Yellowstone's 'landscape of fear' is not as scary as first thought.

"Contrary to popular belief, the wolf is not a round-the-clock threat to elk; it mostly hunts at dawn and dusk, and this allows elk to safely access risky places during nightly lulls in wolf activity," says Kohl, who completed a doctoral degree at USU in 2018 and is lead author of the paper. "Despite their Hollywood portrayal as nighttime prowlers, wolves tend to hunker down at night because their vision is not optimized for nocturnal hunting."

With colleagues Daniel Stahler, Douglas Smith, and P.J. White of the U.S. National Park Service, Matthew Metz of University of Montana, James Forester of University of Minnesota, Matthew Kauffman of University of Wyoming, and Nathan Varley of University of Alberta, Kohl and MacNulty report their findings in an Early View online article of Ecological Monographs. The article will appear in a future print edition of the Ecological Society of America publication. The team's research is supported, in part, by the National Science Foundation.


The researchers revisited data from 27 GPS radio-collared elk that had been collected in the early years after the reintroduction, 2001-2004, but never fully analyzed. These collars recorded the location of each elk every 4-6 hours. This was the first time GPS technology had been used to track Yellowstone elk, and no one imagined that elk might sync their habitat use to the wolf's 24-hour schedule. Little was known about this schedule until researchers first equipped wolves with GPS collars in 2004.

"In the days before GPS, when we tracked wolves by sight and with VHF radio-telemetry, we knew they hunted mainly in the morning and evening, but we didn't know much about what they did at night" says MacNulty, a veteran Yellowstone wolf researcher and associate professor in USU's Department of Wildland Resources and the USU Ecology Center. "GPS data showed that wolves were about as inactive in the middle of the night as they were in the middle of the day."

Kohl used the GPS data to quantify the 24-hour schedule of wolves, and he compared how elk use of risky places -- sites where wolves killed elk -- differed between periods of high and low wolf activity. "Elk avoided the riskiest places when wolves were most active, but they had no problem using these same places when wolves were least active," says Kohl. "An elk's perception of a place as dangerous or safe, its landscape of fear, was highly dynamic with 'peaks' and 'valleys' that alternated across the 24-hr cycle in response to the ups and downs of wolf activity."

The ability of elk to regularly use risky places during wolf downtimes has implications for understanding the impact of wolves on elk and the ecosystem at large. "Our results can explain why many other studies found no clear-cut effect of wolf predation risk on elk stress levels, body condition, pregnancy, or herbivory," says MacNulty. "If our results reflect typical elk behavior, then actual killing rather than fear probably drives most, if not all, of the effect of wolves on elk and any cascading effect on the plants that elk eat such as aspen and willow."

This conclusion runs counter to popular views about the ecological importance of fear in Yellowstone and elsewhere. "Although our study is the first to show how a prey animal uses predator downtime to flatten its landscape of fear, I suspect other examples will emerge as more researchers examine the intersection between prey habitat use and predator activity rhythms," says Kohl.

After 60 years, Isle Royale continues world's longest predator-prey study

IMAGE: 'After 60 years, the Isle Royale wolf-moose project continues. Today, wolves prosper again in several regions of North America. But our relationship with wolves in many parts of the world... view more 

Credit: Sarah Bird/Michigan Tech

Researchers from Michigan Technological University have released the annual Winter Study report detailing updates on the ecology of Isle Royale National Park. For the third year in a row, the Isle Royale wolf population remains a mere two, while the moose population continues to stay above the historic average. Without the pressure of predation, the expanding moose population will have a greater impact on the island's forest ecology.

The study co-authors include Research Professor Rolf Peterson, Professor John Vucetich and Assistant Research Professor Sarah Hoy. They say the heart of the study's success has been the more than 1,000 citizen science volunteers who have bolstered the study's fieldwork efforts in small teams totaling about 40 people each year for the last 30 years. Together, they helped gather enough skulls to document the shrinking moose of Isle Royale, observe seasonal wolf activity and earned more than their fair share of hiking boot blisters.

In terms of population trends, little changed on the island this past year. As Peterson, Vucetich and Hoy write in the report about the last male-female pair of wolves, "there was no evidence of any change in their status, except they are older by a year."

The pair are closely related--both as siblings and as father-daughter--and the inbreeding within the island's isolated wolf population is what contributed to their demise. The wolves' numbers started plummeting in 2009, declining by 88 percent from 24 to 2 wolves for that period; historical levels of wolves typically varied between 18 and 27. The pair, aged eight and ten years old, may have produced a pup several years ago but the female has continued to reject the male as a mate.

One meager hope for new wolves formed briefly in early February. For almost a week, an ice bridge connected the island to the Ontario mainland. However, the ice conditions were rough, the bridge did not last long, and the researchers found no evidence of wolves crossing over. With fewer ice bridges and warmer winters, the chances of wolves recovering naturally is slim to none.

As the wolf population declined and forage remained abundant, the moose population has been able to expand. Counting conditions for the past two winters have not been ideal, but the team estimates the moose population to be around 1,475 members. The population usually numbers between 700 and 1,200 moose. Hoy, who led the skull size study of the island's moose that found their size decreased by 16 percent over 40 years, says we are observing a population in transition.

"Although the effects on body size are quite subtle, there was a marked decline in lifespan over the study period," she says, explaining that wolves are not the only factor affecting moose. The changes in both populations impact the rest of the island, particularly balsam fir, which is a staple winter food for moose. "Maybe the trees can withstand one major source of stress, but with the lack of predation and a changing climate, can it withstand two or more?"

Peterson, who has been a part of the Isle Royale research for the past 50 years, says the island is a unique place to study moose and wolves. Unlike big, complex spaces like Yellowstone, where the cascading effects of wolf populations are still debated among scientists, Isle Royale is a neatly contained ecosystem that can provide insight into other Northwoods settings.

"This is the perfect environment to observe predator-prey interactions--but doesn't make it easy," he says. "We anticipate big things are about to happen, with wolf predation restored, that will once again change the direction of the island's ecosystem. It might take a long time to see the full impact of those changes."

The National Park Service has proposed introducing 20-30 wolves to the island over the next three years. The final environmental impact statement was completed and the identified preferred alternative is to restore wolf predation, but the final decision on the plan is pending as of the Winter Study report publication.

The shrinking moose of Isle Royale

IMAGE: The researchers measured the length, width and height of moose skulls to study the impact of climate change on the iconic Northwoods species. The team measured 662 moose skulls and... view more 

Credit: Sarah Bird/Michigan Tech

Researchers from Michigan Technological University know the smartest way to know a moose is by its brain. Specifically, skull measurements reveal information about body size, physiology and the conditions of a moose's early life. Put together, measurements through time reveal the health of a population and even changes in their environment.
For the booming moose population of Isle Royale, a key species in the world's longest running predator-prey study on the island, skulls have shrunk by about 16 percent over a 40-year period. The results were published recently in Global Change Biology.
Sarah Hoy, a research fellow in the School of Forest Resources and Environmental Science (SFRES) at Michigan Tech, led the study.
"The conditions you're born into have a massive impact on not only how big you are but also how long you're going to live," Hoy says. "This idea isn't new--what we're trying to do is establish how climate warming is affecting this iconic, cold-adapted species. We found evidence suggesting that moose experiencing a warm first winter tended to be smaller as adults and live shorter lives."
The results from the Isle Royale moose study are significant for several reasons, especially taken in the context of nearby moose populations.
In northern Minnesota, moose populations have been halved in the past 12 years. Many ecologists consider three main factors at play: predation, disease and climate change. In particular, the influence of warmer temperatures on moose nutritional condition and moose parasites, including a fatal brain worm parasite that is spread by white-tail deer, which have moved farther north into moose territory as the climate has gotten milder.
"The moose populations in northern Minnesota have tanked," Hoy says. "Climate is considered a main driver, whether it's direct through warmer winter temperatures causing heat stress and influencing the nutritional condition of moose or indirectly by establishing more favorable habitat for white-tail deer."
As Minnesota moose have declined, the Isle Royale moose have flourished, the population growing annually by more than 20 percent for the past six years. There are also no white-tail deer to spread parasites on Isle Royale. Yet the two groups of moose do share a similar climate, so Hoy and her team wondered if the skulls of Isle Royale moose would reveal adverse impacts of climate change.
Moose--who are naturally creatures of the north--prefer the cold. Warmer winters in the Northwoods raise concerns about how animal populations will adapt to climate change.
By measuring the length, width and height of moose craniums--on 662 skulls gathered on Isle Royale by hundreds of citizen science volunteers over four decades--clear patterns emerge. First, the skulls have decreased in size and, second, the evidence suggests that moose calves experiencing a warm first winter tended to be smaller as adults and live shorter lives. Hoy's collaborator Rolf Peterson, an SFRES research professor at Michigan Tech, helped haul in some of the skulls.
"The farthest we had to hike was 20 miles," Peterson says. "These aren't changes you can see out in the field; we're looking for trends over time in the whole population."
Hoy, Peterson and their collaborator John Vucetich, a professor of ecology at Michigan Tech, suggest the trends reflect a population in transition. Part of the Isle Royale moose's transition has to do with another of the island's key species--wolves.
It seems like a paradox: a growing population with shrinking individuals and shorter lifespans. Yet when the ecological balance of food availability and predation are considered, the contradiction makes more sense. As the wolves have died off on the island--only two remained during last year's winter study--the moose population has tripled in the past decade, reaching about 1,600 in the 2017 survey. Competition for food can also contribute to malnutrition and therefore smaller moose.
"Decreasing skull size may be an early indicator of population change," Vucetich says. "We're likely looking at a population in transition, and the healthiest transition would almost certainly involve restoring wolf predation to Isle Royale."
Adapting to climate change is already tough on moose; adding the present day's imbalance in the predator-prey dynamics puts additional stress on the Isle Royale ecosystem. Drawing from six decades of data, the Isle Royale Winter Study will come out later this winter to document the impacts of population change in the island's ecosystem.
In the meantime, the National Park Service plans to release its decision this winter on whether or not to reintroduce wolves to Isle Royale.

Wolves hunting moose undeterred by tailings ponds and pit mines

Wolf behavior undeterred by tailings ponds and pit mines

Study shows wolves hunt moose as usual in the Athabasca Oil Sands

University of Alberta

IMAGE: Two wolves peer into a wildlife camera in Alberta's Athabasca Oil Sands region. view more 

Credit: Wildlife Habitat Effectiveness and Connectivity, 2014

Wolves do not avoid areas of human disturbance when hunting moose in Alberta's oil sands region.
New UAlberta research shows that predation rates of moose have increased near areas of high human disturbance, but low human activity, such as tailings ponds and pit mines.
"Wolves are not avoiding these features," explained UAlberta PhD candidate Eric Neilson, who compared the population density of moose to the distribution of wolf-related moose deaths in the region. "In fact, they are using space near mines as they usually would, demonstrating that these spaces are not a deterrent."
If anything, Neilson says these spaces provide effective hunting ground for wolves.

Environmental changes
When habitat is cleared for mining or oil extraction, there are large changes to the landscape that create barriers around which wolves move. A similar effect, Neilson said, is shown around rivers.
"Wolves are coursing predators. This means that they like to move across the landscape to encounter their prey. It could be that the edge of the mine provides a feature similar to rivers that they can move along and around in the same way," he said.
However, the intensification of wolf activity and moose kills near the edges of these mines and tailings ponds is not shown near camps or upgrader sites, likely due to the presence of humans.

Future investigation
"There is a lot more research to be done in this area," said Neilson, adding the impact upon moose populations is not yet clear. "With any change in habitat that causes changes in animal behaviour, there are many factors to consider and much more we can learn about what is really going on here."

An alternative to wolf control to save endangered caribou

IMAGE: Mountain Caribou in British Columbia, Canada observed during a population census. view more 

Credit: Robert Serrouya

What happens when invasive and native species are eaten by the same predator? If the invasive species is abundant, the native species can go extinct because predator numbers are propped up by the invading species. This process is called "apparent competition" because on the surface it "appears" that the invading and native prey directly compete with each other, but really the shared predator links the two prey.

Apparent competition is an increasing problem, causing endangerment and extinction of native prey as abundant species colonize new areas in the wake of human-caused change to the environment. This is exactly what is happening to the iconic woodland caribou across North America. Prey like moose and white-tailed deer are expanding in numbers and range because of logging and climate change, which in turn increases predator numbers (e.g. wolves). With all these additional predators on the landscape, more caribou become by-catch, driving some herds to extinction.

A short-term solution would be to kill wolves but this can be seen as just a band aid, and is no longer politically acceptable in many jurisdictions. As a more ultimate solution, Serrouya and colleagues used a new government policy and treated it as an experiment, to maximize learning. The new policy was to reduce moose numbers to levels that existed prior to widescale logging, with an adjacent reference area where moose were not reduced. The results of this research are published in an article titled "Experimental moose reduction lowers wolf density and stops decline of endangered caribou," and is published today in the peer reviewed and open access journal PeerJ.

Following the reduction of moose using sport hunting, wolf number numbers declined, with wolf dispersal rates 2.5 × greater than the reference area, meaning that dispersal was the process leading to fewer wolves. Caribou annual survival increased from 0.78 to 0.88 for the Columbia North herd, located in the moose reduction area, but survival declined in the reference area (Wells Gray). The Columbia North herd probably stabilized as a result of the moose reduction, and has been stable for 14 years (2003 - 2017). By expanding their comparison across western Canada and the lower 48 states, they found that a separate herd subjected to another moose reduction was also stable, whereas at least 15 other herds not subjected to moose reductions are continuing to decline.

The results obtained by Serrouya and colleagues are similar to other studies that used more controversial approaches. For example, in Alberta, 841 wolves were removed in the Little Smoky caribou herd over 7 years, but results were as good or better using the less controversial approach of reducing invasive prey (moose). But, population stability is insufficient to achieve recovery goals for caribou, which require population growth. This conclusion suggests that several limiting factors and management levers must be addressed simultaneously to achieve population growth for caribou.

These levers include habitat protection, reducing invading prey, and if needed, short-term and focused predator removal.

Baits may be bolstering bear populations

New research reveals that baits used by hunters have become a substantial portion of black bears' diets. In northern Wisconsin, over 40% of the diet of harvested animals consisted of bait subsidies.

The widespread availability and consumption of these calorically rich baits--often high-sugar foods, such as cookies, donuts, and candies--may be bolstering the bear population density in the region. 

Thirty states permit hunting black bears, 12 of which allow baiting prior to the opening of the hunting season. However, the findings indicate that the goals and consequences of baiting policies should be re-evaluated.

"It's not surprising that bears are eating bear bait, but what is notable is the extent. Not only are these bears consuming bait just before they are harvested, but also throughout their lifetimes, which makes them one of the most highly subsidized populations of bears," said Dr. Rebecca Kirby, lead author of the Journal of Wildlife Management study.

Study doesn't support theory red and eastern wolves are recent hybrids, researchers argue

A team led by University of Idaho researchers is calling into question a widely publicized 2016 study that concluded eastern and red wolves are not distinct species, but rather recent hybrids of gray wolves and coyotes. In a comment paper that will publish Wednesday, June 7, in the journal Science Advances, the team examines the previous study and argues that its genomic data and analyses do not definitively prove recent hybridization -- but rather provide support for the genetic and evolutionary distinctiveness of red and eastern wolves.

"The history of these species is complex and certainly contains evidence for hybridization in the past. The question is timing," said Paul Hohenlohe, an assistant professor of biological sciences in the UI College of Science and the lead author of the comment paper. "The data and analyses aren't actually a good test of recent vs. older hybridization. In fact, the data are consistent with red and eastern wolves having a long evolutionary history as distinct lineages."

Hohenlohe co-authored the paper with an interdisciplinary team that included co-lead author Linda Rutledge, a research associate in the biology department at Trent University in Ontario, Canada; Lisette Waits, a Distinguished Professor in UI's College of Natural Resources Department of Fish and Wildlife Sciences; UI research scientist Jennifer Adams; UI postdoctoral researcher Kimberly Andrews; and other researchers from Trent, the University of Georgia and Northland College.

The team agrees with one conclusion of the previous study: Admixture is a part of the evolutionary history of North American canids, and conservation policy needs to take into account naturally occurring hybridization and population admixture. But they urge policymakers not to close the case on the origins of red and eastern wolves when making conservation decisions.

"Policymakers are making decisions about how much money, effort and energy to put into recovery and management efforts of the red wolf and eastern wolf," said Waits, who has served on U.S. Fish and Wildlife Service recovery teams for the red wolf. "It is important for them to understand that the conclusions stated in the vonHoldt et al paper are not universally supported by the scientific community, and there are alternative interpretations and remaining questions about the evolutionary history of canids in North America."

The UI-led team addresses several concerns with the previous study, which was led by Princeton University's Bridgett vonHoldt and published in Science Advances in July 2016. The team questions the vonHoldt study's use of genomic data from a few individual coyotes and eastern wolves that may not be the best representatives of those groups, as well as the authors' conclusion that genomic data demonstrate a lack of unique ancestry in red and eastern wolves.

The team's review of the vonHoldt study's analyses of genomic data finds the data do not establish definitive evidence for a recent hybrid origin of red and eastern wolves, but rather are consistent with multiple evolutionary possibilities. These possibilities include red wolves originating from a hybridization event tens of thousands of years ago, or diverging as a distinct lineage as long as 100,000 years ago and experiencing some subsequent hybridization.

The UI-led team finds that other data from the previous study, such as the amount of unique genetic variation found only within red or eastern wolves, further support the genetic distinctiveness of these taxa.

Hohenlohe, Waits and their collaborators are conducting further analyses about red and eastern wolf origins, and expect to continue to generate new data and hypotheses about the evolutionary relationships among these species, the gray wolf and the coyote.

"Genomics is an exciting new contribution to wildlife conservation, but it brings with it a responsibility to provide a coherent interpretation of complex data within the context of natural history," Rutledge said. "This is especially important for species at risk of extinction where the consequences involve the permanent loss of evolutionary potential. We get closer to the evolutionary truth when we use a holistic approach that includes multiple sources of information."