The Yellowstone Wolf Controversy

Summary

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Short Wave (NPR): "The Yellowstone Wolf Controversy"

Air Date: August 20, 2025
Host: Emily Kwong
Producer: Burleigh McCoy
Featured Scientists: Eric Larson, William "Bill" Ripple, Bob Beshta, Lanie Bryce, Avery Schaller, Tom Hobbs, Sisto Hernandez

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Overview

This episode explores the controversy surrounding the legacy of wolf reintroduction in Yellowstone National Park, three decades after wolves were brought back to the region. While the dominant narrative credits wolves with transforming the ecosystem (sparking a "trophic cascade" that revitalized trees, beavers, and rivers), new scientific findings reveal a more complex, nuanced picture. The hosts and guests examine key research, debate the legacy, and discuss the real-world consequences of oversimplifying Yellowstone's story.

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Key Discussion Points and Insights

1. The Yellowstone Wolf Narrative: Where Did It Come From? (00:30–03:19, 04:18–06:29)

• Background: Wolves, once native to Yellowstone, were wiped out in the early 20th century. In 1995, they were reintroduced after decades of absence.

• Popular Narrative: The return of wolves led to declining elk numbers, rebounding trees and shrubs, the return of beavers, and changed river courses—a classic "trophic cascade."

  "That wolves impacted the density or behavior of elk so much that the effects cascaded, trickled down to aspens and willows, which affected beavers and songbirds and eventually changed the course of the rivers."
  — Avery Schaller, Wildlife Ecologist (01:58)

• Media Impact: The dramatic story stuck, spreading widely in documentaries, articles, and public imagination.

• Early Research: Based on observations like those from Eric Larson and his advisor William Ripple, connecting wolf presence to improved aspen growth.

2. Challenging the Simplistic Cascade (06:29–11:02)

• Differing Scientific Views:

  • Bill Ripple & Bob Beshta: Advocated strongly for the wolf-driven cascade hypothesis.
  • Eric Larson & Collaborators: Focused on long-term, broad data, finding that aspen recovery was uneven (“patchy”) and could not be attributed to wolves alone.
  • Quote:

    "Some of them are doing really, really well. Some of them haven't recovered at all. Some have died out entirely. So it's a very patchy response."
    — Lanie Bryce, Scientist (07:06)

• Key Data Points:

  • Elk numbers dropped after wolves returned (from a 1994 high of ~20,000 to around 12,000), but so did other factors like harsh winters and increased hunting outside park boundaries.
  • Wolves tend to kill old/young elk, but hunters take prime-aged females—a more significant hit to population numbers.
  • Elk still browse in some areas with wolf presence; they’re not universally "scared off."

  "Hunters are often killing prime age females, whereas wolves usually kill the very old or the very young."
  — Burleigh McCoy (08:29)

  "We didn't really see much different in elk browsing activity depending on wolf risks."
  — Lanie Bryce (08:53)

• Further Complications:

  • Cougars and bears, also elk predators, were in decline when wolves disappeared, possibly contributing to the elk population boom.
  • Beavers' recovery ties to human efforts: scientists relocated beavers north of the park in the 80s and 90s, some later returned to Yellowstone.

  "Beavers have made a comeback partially because of humans."
  — Emily Kwong (10:17)

3. The Dangers of Oversimplification (11:02–14:28)

• Continuing Scientific Debate: Ripple and Beshta defend the strong cascade view, publishing new papers, while others rebut with alternative interpretations and evidence.

  "Arrows fired straight into each other's research like that billboard."
  — Emily Kwong (11:54)

• Broader Consequences: Decisions around wolf reintroduction in other regions reference Yellowstone’s story—sometimes using oversimplified expectations that don't translate elsewhere.

  • Quote:

    "If people expect wolves to have these sweeping environmental changes, especially in short timeframes, it’s setting up that community for failure."
    — Burleigh McCoy (12:11)

• Regional Differences & Human Conflict: Places considering wolf reintroduction may lack the vastness of Yellowstone, leading to more conflict with agriculture and ranchers.

  • Case Example: Sisto Hernandez, White Mountains rancher in Arizona, describes financial burdens imposed by wolves and local coexistence efforts.

  "There isn't much to generate revenue on the reservation. And ranching is one of those things that we can do and it limits us on that."
  — Sisto Hernandez (13:17)

  • Ecologists warn that focusing only on wolves (a "single species approach") distracts from broader ecological threats and realities.

  "When you get this kind of tunnel vision on single species conservation, it can really ignore other, bigger threats to wolves and other species that also matter."
  — Avery Schaller (13:53) "There’s a lot of good people doing a lot of the work in the middle, and ecology is really complex. And we’re still in the early stages of seeing exactly how wolves impact the Yellowstone ecosystem."
  — Avery Schaller (14:15)

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Memorable Quotes & Moments

• "This is something that scientists told me over and over again, that if we get the Yellowstone narrative wrong, people could use it to justify wolf reintroduction in places very different from Yellowstone, where more people live, so more potential conflicts."
  — Burleigh McCoy (13:30)

• Humorous aside:

  "Otherwise it'd be like an Agatha Christie level murder mystery with many people in the drawing room with different weapons."
  — Emily Kwong (11:11)

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Timestamps for Key Segments

| Segment | Start | End | |-----------------------------------------------------|---------|--------| | Opening & setup of Yellowstone wolf debate | 00:18 | 03:19 | | The origins of the wolf narrative | 04:18 | 06:29 | | Contradictory long-term research on aspen recovery | 06:29 | 07:30 | | Elk population changes and the hunter variable | 07:47 | 08:53 | | Beavers, willows, and human intervention | 09:47 | 10:49 | | Critique of the "chain-reaction" narrative | 10:49 | 11:11 | | New research & ongoing scientific disagreements | 11:18 | 11:54 | | Policy consequences & regional reintroduction | 12:11 | 13:01 | | Rancher perspective and coexistence challenges | 13:01 | 13:30 | | Warnings about single-species tunnel vision | 13:53 | 14:28 |

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Takeaways

• The Yellowstone wolf story is more than a simple tale of predator, prey, and ecosystem restoration; it’s a multifaceted web influenced by human actions, environmental changes, and the unique complexities of place.
• Scientific understanding is still evolving and fiercely debated, with ongoing disagreements about the scale and mechanism of wolf impacts.
• Oversimplified ecological stories can have real consequences, shaping public opinion and policy in ways that may not serve people or wildlife well in different contexts.
• Successful conservation requires nuance, site-specific understanding, and humility—acknowledging both the limits of our knowledge and the multiplicity of ecological influences.

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For science lovers and policymakers alike, this episode is a powerful reminder: In ecology, beware the simple story. The full truth is far more wild, intricate, and, yes—still unfolding.

Transcript

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[Emily Kwong]

You're listening to short wave from NPR. Hey, Shortwavers. Emily Kwong here with producer Burleigh McCoy. Hi, Burleigh.

[Burleigh McCoy]

Hey, Emily.

[Emily Kwong]

Okay, what do you got for us today?

[Burleigh McCoy]

So I've brought you a complicated story about wolves in Yellowstone National Park.

[Emily Kwong]

I've never been to Yellowstone. I've always wanted to go. Are the wolves a big deal there?

[Burleigh McCoy]

Yeah. So I live in Montana and most anyone in the mountain west will tell you people have big feelings about wolves here.

[Emily Kwong]

Yeah.

[Burleigh McCoy]

Some years ago, I remember driving by this huge billboard with a picture of a majestic looking wolf with a message like protect the wolves. And someone had shot an arrow through its forehead.

[Emily Kwong]

Oh, that sends a message. Why?

[Burleigh McCoy]

Well, wolves are predators and some people view them as a menace. Even though they used to be native in the area, they were hunted almost to the point of extinction in the late 18 and early 1900s, often with poison that killed other animals. It was nasty. Then 30 years ago, around a few dozen wolves were reintroduced. And now there's a big scientific debate about how they've affected the ecosystem.

[Emily Kwong]

Okay, 30 years of wolf reintroduction, we're recognizing that anniversary with this episode. What is the debate?

[Burleigh McCoy]

Well, first I'll say most everyone agrees that the absence of wolves and other predators caused a spike in the elk population. And these elk ate up all the trees and shrubs, especially by the rivers. And because of this, the beavers left. So no more dams. The rivers changed. They got deeper and faster. So wildlife ecologist Avery Schaller says after the wolves came back, the story goes.

[Avery Schaller]

That wolves impacted the density or behavior of elk so much that the effects cascaded, trickled down to aspens and willows, which affected beavers and songbirds and eventually changed the course of the rivers.

[Burleigh McCoy]

She told me a few years after the first wolf reintroduction, one group of scientists started detailing this ecosystem wide change and claiming the wolves were causing these huge ripple effects. The media picked up the story and ran with it. And to a large extent, that's the story that stuck.

[Emily Kwong]

You sound skeptical of this wolf narrative. Is there another side to the story?

[Burleigh McCoy]

There is. I talk to a lot of scientists who say this story is way too simple and overstated and that wolves are just one piece of a much larger puzzle for how elk numbers dropped.

[Emily Kwong]

So today on the show, we Explore the legacy of wolf reintroduction in Yellowstone national park three decades on.

[Burleigh McCoy]

Plus how some scientists think wolves effects on the ecosystem have been overplayed and the potential consequences of getting the narrative wrong.

[Emily Kwong]

You're listening to Short Wave, the science podcast from npr.

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[Emily Kwong]

Okay, Burleigh, so we're talking about a dispute among scientists regarding this Yellowstone wolf narrative. So for a long time, the story went that when wolves were reintroduced in 1995, so 30 years ago, the entire ecosystem became altered. Where did that narrative come from?

[Burleigh McCoy]

So it really starts with data collected in the 90s by then graduate student Eric Larson at Oregon State University.

[Eric Larson / Sisto Hernandez]

I wasn't looking at, you know, wolves particularly at all. I was looking for reasons why aspen wasn't reproducing in Yellowstone Park.

[Emily Kwong]

Okay, so he's a tree guy, this Eric.

[Burleigh McCoy]

Yes. And this was a few years after wolves were reintroduced in northern Yellowstone. Eric was looking at current and archival tree ring data, and he found that growth had fallen off around the 1920s.

[Emily Kwong]

What happened in the 1920s?

[Burleigh McCoy]

Well, that's around the time humans had killed so many wolves that they were basically locally extinct. And the technical term for this is extirpated. So Eric and his adviser, William Ripple, he goes by Bill, hypothesized that because the wolves were gone, elk numbers exploded and those elk started eating the trees.

[Emily Kwong]

I had no idea that elk ate trees. They. They sound voracious. So, so essentially their hypothesis was less wolves meant less aspen trees.

[Burleigh McCoy]

Yes, aspen and other vegetation like willows. So after wolves were brought back, the natural question became, did the trees come back Too so in 2001, they published a paper where they looked at tree growth in more than 100 stands of aspen, this time looking at the height of the tallest tree in the stand. And they found trees were growing better where wolves spent more time.

[Emily Kwong]

Wow.

[Burleigh McCoy]

Presumably because elk were afraid of the wolves and leaving the trees alone.

[Emily Kwong]

Okay, I can see how a straightforward narrative then emerged from this finding that the livelihood of the trees was somehow linked to the wolves.

[Burleigh McCoy]

Yeah, exactly. And Eric's advisor, Bill, took off with this line of reasoning. Along with another scientist, Bob Beshta, they started publishing more papers about how wolves have these cascading ecosystem effects.

[Emily Kwong]

Okay, what does Eric think of all of that? The guy we met in the beginning?

[Burleigh McCoy]

Well, he went in a different direction. Eric kept going back to those 100 Aspen stands year after year, diligently collecting data.

[Eric Larson / Sisto Hernandez]

I just had a feeling that if I stuck with it for 20 years, I could show something important.

[Burleigh McCoy]

And he ends up teaming up with another group who use the same data set, but instead they look at average growth.

[Emily Kwong]

Okay. Instead of just the tallest tree.

[NPR Sponsor Announcer]

Right.

[Burleigh McCoy]

And Eric and his new collaborators come to a different conclusion about the aspen. Here's one of those scientists, Lanie Bryce.

[Lanie Bryce]

Some of them are doing really, really well. Some of them haven't recovered at all. Some have died out entirely. So. So it's a very patchy response.

[Burleigh McCoy]

And Bob and Bill agree the recovery is kind of patchy.

[Emily Kwong]

Okay.

[Burleigh McCoy]

Where those two teams disagree is how the wolves influenced this recovery. Bob and Bill say wolves have unmistakably triggered this change. Eric and his team say it's more complicated than that.

[Emily Kwong]

Okay, so people agree the trees have come back. They agree the recovery's been kind of patchy. They don't agree on what the w. Wolves had to do with it. And I guess the real question I have is about the. The creature in between the elk. Have elk numbers gone down since the wolves came back?

[Burleigh McCoy]

Short answer, Emily. Yeah, there were around 12,000 elk when the wolves were wiped out in the 20s. And the population grew over the following decades, reached a high in 1994 of close to 20,000.

[Emily Kwong]

That's a lot of elk.

[Burleigh McCoy]

Yeah. And that number quickly plummeted back down to around 12,000 after wolves were reintroduced the following year. But, Emily, there's another variable here.

[Emily Kwong]

What's that?

[Burleigh McCoy]

Hunters.

[Emily Kwong]

Oh, humans.

[Burleigh McCoy]

Humans.

[Emily Kwong]

So, wait, people can hunt in Yellowstone?

[Burleigh McCoy]

No, not in Yellowstone. Hunting is prohibited in the park. But the winter of 96, 97, was really harsh, and that pushed a lot of elk outside the park in search.

[Emily Kwong]

Of food, which exposed them to hunters.

[Burleigh McCoy]

Exactly. That year, hunters killed more than 3,000 elk. And hunters are often killing prime age females, whereas wolves usually kill the very old or the very young young. So many scientists say hunters had a bigger impact on the elk population than wolves. And on top of that, Laney, the scientist from earlier who saw the patchy aspen recovery, said they looked at where elk were spending their time, and we.

[Lanie Bryce]

Didn'T really see much different in elk browsing activity depending on wolf risks.

[Burleigh McCoy]

Meaning elk might avoid eating aspen in some areas at certain times because wolves are there, but they're not avoiding the area altogether.

[Emily Kwong]

Oh, that's a real plot twist. So it's not true that the elk are just avoiding areas where wolves are? There are some places perhaps where wolves and elk are coexisting.

[Burleigh McCoy]

Yeah. And this finding has shifted the narrative. Wolves may be eating elk, but they aren't scaring them away entirely. And Emily, at the same time wolves disappeared, humans were also killing two other predators of elk. So cougars and bears. And their decline likely also contributed to the elk boom.

[Emily Kwong]

All right, so we got cougars and bears and wolves. It's not just the wolves eating the elk. And that's the end of the story.

[Burleigh McCoy]

And then there are the beavers.

[Emily Kwong]

How many animals are involved in this separately?

[Burleigh McCoy]

I know, I'm just going to bring the one more in. Okay, so there's a lot. Here's the situation. Beavers need these river shrubs called willows for food and building their dams. And during the elk boom, elk ate those willows, so the beavers moved out.

[Emily Kwong]

These elk just won't quit. That's what I'm also learning from this story, is these elk, when they want to eat trees, they're going to make.

[Burleigh McCoy]

Sure that happens, you know, and I'll gotta eat. But Emily, beavers have made a comeback partially because of humans.

[Emily Kwong]

So, like, humans are one of the biggest drivers of change in Yellowstone.

[Burleigh McCoy]

Yeah. So scientists relocated dozens of beavers in the 80s and 90s in the area just north of the park. And over time, some of them moved into the park.

[Emily Kwong]

Wow.

[Burleigh McCoy]

Tom Hobbs, an ecologist at Colorado State University, has studied beavers and willows in the area for the last couple decades. And he says beavers have returned to the bigger streams and rivers in Yellowstone, but they're too big for them to a dam. Which means maybe the return of the beavers hasn't changed the course of the rivers.

[Emily Kwong]

Yeah. Okay, so any, any narrative that is simplistic is just not going to work in Yellowstone, especially the one that the wolves affected. The elk which affected the trees, which affected the beavers, which affected the rivers. It's again, all too simplistic.

[Burleigh McCoy]

Yeah, and that's not to mention other complicating factors that we can't really get into in the length of our podcast. So not going to go there. But just know there are a lot more.

[Emily Kwong]

Well, otherwise it'd be like an Agatha Christie level murder mystery with many people in the drawing room with different weapons.

[Burleigh McCoy]

Isn't it already though?

[Emily Kwong]

Yeah. So, Burley, I have a question. Those scientists, Bill and Bob, who originally linked wolves to this environmental cascade were like, it was the wolves. What do they have to say about all this new data?

[Burleigh McCoy]

So they're doubling down. Earlier this year they published a paper saying the trophic cascade in Yellowstone, which they say was due to wolf's and cougars, was stronger than most trophic cascades reported globally. And other scientists just published a pre print rebuttal saying that analysis was flawed and that the environmental effects of wolves weren't nearly as strong as they're suggesting.

[Emily Kwong]

Arrows fired straight into each other's research like that billboard. Outside of uncovering truth for truth's sake or why is it so important to get this story right, the legacy of the wolves in Yellowstone and their reintroduction.

[Burleigh McCoy]

Because in response to that very simple narrative we started the episode with people in other areas are pushing to reintroduce wolves where they live in an effort to restore the ecosystem. And they're often using Yellowstone to justify it. But if people expect wolves to have these sweeping environmental changes, especially in short timeframes, it's setting up that community for failure.

[Emily Kwong]

That's a fascinating takeaway. Yeah. Because also in addition to it being a mistake to overemphasize the ecological power of wolf reintroduction, I'm guessing not every place is like Yellowstone, which, which has these wide open swathes of land. You know, every region is different.

[Burleigh McCoy]

Exactly. And that brings up a huge hurdle in wolf reintroduction. Clashes with people. I talked to Sisto Hernandez, a rancher in the White Mountains in Arizona on.

[Eric Larson / Sisto Hernandez]

Both sides of the border. My family's been in ranching for time immemorial.

[Burleigh McCoy]

So wolves were reintroduced around there in the late 90s. And he's part of his tribe's council on creating a coexistence plan to compensate ranchers for livestock losses. And he doesn't like that the wolves are there.

[Eric Larson / Sisto Hernandez]

There isn't much to generate revenue on the reservation. And ranching is one of those things that we can do and it limits us on that.

[Burleigh McCoy]

And this is something that scientists told me over and over again that if we get the Yellowstone narrative wrong, people could use it to justify wolf reintroduction in places very different from Yellowstone, where more people live, so more potential conflicts. They also said focusing on wolves ignores a lot. Here's Avery again, the wildlife biologist from the beginning of the episode.

[Avery Schaller]

When you get this kind of tunnel vision on single species conservation, it can really ignore other, bigger threats to wolves and other species that also matter.

[Burleigh McCoy]

She says it's easy to focus on these grand narratives and people who see wolves as either menace or savior, but.

[Avery Schaller]

There'S a lot of good people doing a lot of the work in the middle, and ecology is really complex. And we're still in the early stages of seeing exactly how wolves impact the Yellowstone ecosystem.

[Emily Kwong]

Definitely more questions than answers, but a lot of nuance. Producer Burleigh McCoy, hats off to you. Thank you for bringing us this story.

[Burleigh McCoy]

You're welcome.

[Emily Kwong]

This episode was produced by Hannah Chin and Rachel Carlson. It was edited by our showrunner Rebecca Ramirez and fact checked by Burley and Tyler Jones. The audio engineer was Kwesi Lee. I'm Emily Kwong. Thanks for listening to SHORTWAVE from npr.

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