Editor's note: This is the second in a series of articles looking at the impact of reintroducing wolves in Yellowstone National Park 25 years ago. Be sure to read part one.
YELLOWSTONE NATIONAL PARK — A group of wolves from Jasper National Park in Alberta, Canada, arrived at Yellowstone National Park on Jan. 12, 1995. Twenty-five years later, wolf reintroduction remains controversial with lasting ramifications for people, livestock and nature.
In an effort to separate fact from fiction, this is the second in a series of articles that will explain what we know and don't know by allowing federal, state and local wildlife and livestock managers to respond to common questions and concerns regarding wolves.
We've addressed why wildlife officials reintroduced wolves and looked at the numerous claims relating to wolf taxonomy and distribution. Now, we will examine the factual effects of reintroduction on Yellowstone’s ecology.
Claim: Wolves are ‘destroying’ elk populations
Terms such as "destroy," though commonly invoked, are incredibly subjective. But that is not why this claim is fiction.
It is true that some elk herds in and around Yellowstone have seen drastic reductions since wolf reintroduction, but the reductions are likely the result of dozens of factors. Let’s dive into the facts.
In the previous article, we discussed whether relocated wolves are, as often claimed, larger and thus unfairly and unnaturally advantaged in preying on Yellowstone’s elk population. The irony of this claim is that Jasper National Park’s wolves (where the first reintroduced wolves originated) had been preying on Yellowstone elk for the better part of a century prior to their reintroduction to Yellowstone National Park.
Like Utah, Nevada, Colorado and other states — Jasper’s elk population had been decimated by human predation near the beginning of the 20th century. And like the above mentioned states, wildlife managers from Canada turned to Yellowstone National Park to help reestablish the region’s elk in 1920.
Why, then, are elk numbers shrinking if wolves are not unfairly advantaged?
An examination of Yellowstone’s much-discussed northern elk herd, which reduced from nearly 20,000 animals to between 4,000 and 6,000 animals — a reduction of about 75% — offers a great deal of clarity. Following the predator eradication programs of the 19th and 20th centuries, ungulate populations ballooned and became hyper-abundant in some areas.
"There was a lot of discussion at the time (of wolf reintroduction), that that was too many elk from a habitat health standpoint," said Quentin Kujala, wildlife management section chief for Montana Fish, Wildlife and Parks.
Beyond the habitat degradation caused by artificially high elk numbers, the average age of Yellowstone’s elk was also unnaturally high without adequate predators to cull the herd. When wolves were reintroduced, they "came into a landscape with abundant food and vulnerable animals," said Dan Stahler, a wolf biologist for Yellowstone National Park, in an interview published on Facebook.
Following reintroduction, wolf numbers increased to a peak of 174 wolves and 16 packs.
"But the population was erratic," said Yellowstone’s chief wildlife biologist, Doug Smith in another interview also published on Facebook, citing disease and other limiting environmental factors.
The park's current population sits at roughly 100 wolves and eight packs, and has been stable for about a decade, Smith said.
"Simultaneous to wolf reintroduction, cougars ... naturally recolonized the park. Grizzly and black bear numbers were growing and robust," Stahler added.
The recovery of large predators also coincided with heavier human predation "outside the park (that) was designed to reduce the number of elk," Stahler said. Kujala agreed, pointing out that humans were a "part of the predator mix" reducing elk.
Additional pressures further drove the decline in elk numbers, including habitat loss or depredation, drought, severe winters, disease, wildfires, pine beetle infestations, management changes as well as land ownership changes (outside the park) that disrupted both elk habitat and access to elk. All of those conditions of the landscape have occurred since wolves were reintroduced.
A detailed examination of natural predation further refutes fears regarding the influence of wolves on the elk population.
"When Fish, Wildlife and Parks looked at elk in the (Bitterroot region) in response to elk population concerns that were being tied in a perception context to the new arrival of wolves, we actually found that cougars … were first in line when it relates to feeding on elk," Kujala explained. A number of studies from Idaho Fish and Game came to the same conclusion, including in Idaho’s Salmon Region, where wolves were also reintroduced 25 years ago. Surveys of predation at Yellowstone also conclude that bears remain the top predator of elk calves during the summer.
"It’s the mix," Kujala said. "(Wolves are) the last addition to what is in the Yellowstone area, now a complete, fully restored … complex of predators on the landscape."
Ascribing both real and perceived reductions in elk numbers to just, or mainly wolves neglects the majority of a complex ecological equation. Efforts to quantify the effect of wolves on elk numbers are ongoing, but it's clear other factors have contributed to documented declines.
Today, Yellowstone’s northern elk herd "is at or near to the population objective," Kujala added. But he also says "there are a lot of folks that, rather than seeing a population objective, they see that as less than it was."
He said viewing and hunting opportunities have been affected "and undoubtedly some people see that as a move toward ‘bad.’ The folks that like to focus on riparian health, they’ll see that as a positive."
"We have fewer elk now but it’s probably a healthier number, more in balance with what elk numbers should be," Smith added. "Elk numbers have stabilized. Bear and cougar and wolf numbers have stabilized. We have what we believe to be a healthier landscape. ... we’re kind of in a new era."
Regarding Yellowstone’s elk, Smith said: "They’re probably one of the healthiest elk herds in North America because they are culled by predators."
But what about moose populations?
Evidence suggests that moose weren’t particularly common in the Yellowstone until the latter half of the 1800s. Following predator control programs, fire suppression and hunting restrictions, moose numbers increased. There were an estimated 1,000 moose in Yellowstone in the 1970s, but that number dropped to about 200 by 1996.
The northern moose population, in particular, was reduced by at least 75% in the 1980s. The 1988 fires were particularly impactful on moose numbers, given the loss of mature forests, which are a crucial moose habitat. Many moose who survived the ’88 fire season died during the following winter, likely as a result of lost winter habitat and foraging opportunities.
As has been demonstrated above, correlation does not equal causation. But in the case of moose populations, there isn’t even a correlation. Moose numbers in Yellowstone crashed before wolves were reintroduced. While predation remains an influencer, wildlife managers have also noticed similar drops in areas not inhabited by wolves or grizzly bears. Among the most likely culprits are a warming climate, loss of mature forests and parasites.
Falling moose numbers across the west remain a point of concern and can leave interested parties scrambling for explanations. What data that is available is more than adequate to dissipate associations between wolf reintroduction and drops in moose populations.
Claim: Wolves perpetrate 'sport/surplus killings'
Fact and fiction
The specter of surplus or sport killing deeply troubles many hunters and livestock producers. In acknowledging those concerns, it’s important that we take the time to separate what we know and don’t know about the so-called "surplus killing."
"We, as humans ... don’t see a whole lot of the wild world in the backcountry, in the middle of the night, like we see domestic animal husbandry work," Kujala said. "In that context, there are instances where people (discover) a mass of multiple carcasses. It’s connected to predators ... not just wolves."
Mass killings rare, according to Kujala, but domestic animals have "additional vulnerabilities." We’ll discuss the frequency and scale of livestock predations in our next article as we examine the effects of wolf reintroduction on people. As for the question of whether wolves kill indiscriminately or for sport, Kujala said, "There’s not a whole lot of evidence to support that."
Smith, speaking of predation on elk, is more definitive.
"Wolves do not kill for sport. That is a fact," he said. "They risk injury or death. When you attack something five to seven times as large as you, that ain’t a fair fight. ... (Wolves) prey in a risk-averse fashion. ... If the risk equation balances out in their favor, (wolves) will kill more than they can immediately eat. But underline the word immediately."
Smith stresses that when wolves kill multiple animals they will "cycle back" over an extended period and eat everything if the kill remains undisturbed.
"Many people believe wolves are super killer ... that’s simply not true," Stahler added. "There are limits to wolf hunting ability that are defined by biology. Wolves are only successful between 5 and 15 percent of the time. ... A prime-age cow elk in Yellowstone between the ages of 2 and about 13, is virtually invulnerable to wolf predation."
This appears to be confirmed in the 2019 elk and deer press release from Idaho Fish and Game, which reports adult cow elk survival at 98%. It, again, reports that mountain lions, not wolves, are the top natural predators of elk cows and calves. While wolves, at times, prey on healthy animals, Smith said, "On average, wolves do not kill healthy elk. It’s too hard."
So, do wolves kill indiscriminately for sport? The consensus among biologists is no.
Will they kill more than they can eat in the short-term? On rare occasions, yes, especially "if the risk equation balances in their favor." But wolves subsist on those kills long term if they are not pushed off the kill by humans or other predators.
Claim: Wolves Changed Yellowstone’s Rivers.
In the case of this claim, the truth is more complex than just fact or fiction.
The term Trophic Cascade has gained increased recognition over the past decade in no small part because of a viral video titled "How Wolves Changed Rivers," which is largely based on an examination of riparian health following the reintroduction of wolves to Yellowstone.
Indeed, Yellowstone has seen a remarkable regeneration of willows, cottonwoods and aspens over the past couple decades, which has, in turn, created habitat and opportunities for a wide assortment of wildlife. But are wolves the architects of this miracle?
Ironically, proponents of this wolf-centric hypothesis, like those who claim wolves are "destroying" elk and moose populations, have exaggerated the role wolves play. The loss of Yellowstone’s predators, like wolves, did indeed contribute to the hyper-abundance and overgrazing by herbivores like elk. But as we’ve discussed above, wolf reintroduction was in no way an isolated event.
There is strong evidence that wolves, in the company of Yellowstone’s other predators, by preying on ungulates have played an important role in restoring the health of Yellowstone's forests and waterways. However, it’s also important to note that in many ways the origin of Yellowstone’s rejuvenation remains the subject of study and ecological debate.
Smith, himself, regards the video as "a little bit far-flung" but adds "there is a pearl of truth to it."
The key term in the story of Yellowstone’s seemingly miraculous rejuvenation is biodiversity. Smith put it this way:, "Having a lot of different kinds of things at moderate numbers is better than having a lot of any one thing."
"Prior to (predator recovery), we had a lot of elk, we had a lot of coyotes, and we had very little things like willow and aspen and songbirds and beavers," he said.
With the restoration of Yellowstone’s carnivores (wolves being the most high profile, "all the parts of the system are in place … and it’s changed how Yellowstone looks," Smith continued. Adding in a recent Facebook live video: "All the mammals that were here at the time of Christopher Columbus are here now. That’s a great thing to celebrate."
Make sure to stay tuned for our third and final article in this series, which addresses the impact of wolf reintroduction on humans. Please feel free to share your thoughts in the comments.