The Yellowstone Wolf Controversy

Thirty years ago, park rangers reintroduced grey wolves into Yellowstone National Park. They wanted to restore the ecosystem and get the elk population, which had decimated the plant community, in check. And it worked – or so the popular narrative suggests. But is it really so simple? Today on the show, we explore how the Yellowstone ecosystem has changed since wolves returned and whether those changes can really be pinned solely on wolves. Plus, how the narrative of the Yellowstone wolf legacy could affect wolf reintroduction elsewhere. Curious about other science controversies? Email us at [email protected] mailto:[email protected]. Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:00Speaker 00

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• 0:21Emily Kwong?

  Hey, Short Wavers. Emily Kwong here with producer Burley McCoy. Hi, Burley.

• 0:24Speaker 02

  Hey, Emily.

• 0:25Emily Kwong?

  OK, what do you got for us today?

• 0:26Speaker 02

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

• 0:31Emily Kwong?

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

• 0:35Speaker 02

  Yeah, so I live in Montana, and most anyone in the Mountain West will tell you, people have big feelings about wolves here.

• 0:42Emily Kwong?

  Yeah.

• 0:42Speaker 02

  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.

• 0:53Emily Kwong?

  Oh, that sends a message. Why?

• 0:56Speaker 02

  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.

• 1:21Emily Kwong?

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

• 1:30Speaker 02

  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...

• 1:54Speaker 03

  The story goes 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.

• 2:12Speaker 02

  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.

• 2:30Emily Kwong?

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

• 2:35Speaker 02

  There is. I talked 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.

• 2:46Emily Kwong?

  So today on the show, we explore the legacy of wolf reintroduction in Yellowstone National Park, 30 decades on.

• 2:53Speaker 02

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

• 3:02Emily Kwong?

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

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• 4:19Emily Kwong?

  OK, Burley, 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?

• 4:37Speaker 02

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

• 4:45Speaker 05

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

• 4:55Emily Kwong?

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

• 4:58Speaker 02

  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.

• 5:10Emily Kwong?

  What happened in the 1920s?

• 5:11Speaker 02

  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 extrapated. So Eric and his advisor, William Ripple, he goes by Bill, hypothesized that because the wolves were gone, elk numbers exploded, and those elk started eating the trees.

• 5:29Emily Kwong?

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

• 5:40Speaker 02

  Yes, aspen and other vegetation like willows. So after wolves were brought back, the natural question became, did the trees come back too?

• 5:48Emily Kwong?

  Okay.

• 5:49Speaker 02

  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.

• 6:02Emily Kwong?

  Wow.

• 6:03Speaker 02

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

• 6:08Emily 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.

• 6:17Speaker 02

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

• 6:30Emily Kwong?

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

• 6:33Speaker 02

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

• 6:42Speaker 05

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

• 6:50Speaker 02

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

• 6:56Emily Kwong?

  Okay, instead of just the tallest tree.

• 6:58Speaker 02

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

• 7:06Emily Kwong?

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

• 7:15Speaker 02

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

• 7:19Emily Kwong?

  Okay.

• 7:19Speaker 02

  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.

• 7:31Emily 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 wolves had to do with it. And I guess the real question I have is about the creature in between, the elk. Have elk numbers gone down since the wolves came back?

• 7:47Speaker 02

  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.

• 8:00Emily Kwong?

  That's a lot of elk.

• 8:01Speaker 02

  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.

• 8:10Emily Kwong?

  What's that?

• 8:11Speaker 02

  Hunters.

• 8:12Emily Kwong?

  Oh, humans.

• 8:12Speaker 02

  Humans.

• 8:13Emily Kwong?

  So wait, people can hunt in Yellowstone?

• 8:16Speaker 02

  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 of food.

• 8:27Emily Kwong?

  Hmm, which exposed them to hunters.

• 8:29Speaker 02

  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. 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...

• 8:53Emily Kwong?

  We didn't really see much different in elk browsing activity depending on wolf risks.

• 9:00Speaker 02

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

• 9:09Emily 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?

• 9:21Speaker 02

  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.

• 9:41Emily 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.

• 9:48Speaker 02

  And then there are the beavers.

• 9:49Emily Kwong?

  How many animals are involved in this?

• 9:51Speaker 02

  I know, I know. I know, I'm just gonna 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.

• 10:06Emily 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 gonna make sure that happens, you know?

• 10:12Speaker 02

  And elk gotta eat. But Emily, beavers have made a comeback, partially because of humans.

• 10:18Emily Kwong?

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

• 10:21Speaker 02

  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.

• 10:30Emily Kwong?

  Wow.

• 10:31Speaker 02

  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 dam, which means maybe the return of the beavers hasn't changed the course of the rivers.

• 10:50Emily Kwong?

  Yeah, okay. So any, any narrative that is simplistic is just not gonna 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.

• 11:02Speaker 02

  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 gonna go there, but just know there are a lot more.

• 11:12Emily Kwong?

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

• 11:18Speaker 02

  Isn't it already, though?

• 11:20Emily 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?

• 11:31Speaker 02

  So they're doubling down. Earlier this year, they published a paper saying the trophy cascade in Yellowstone, which they say was due to wolves and cougars, was stronger than most trophy 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.

• 11:55Emily Kwong?

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

• 12:11Speaker 02

  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.

• 12:33Emily 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 has these wide open swaths of land. You know, every region's different.

• 12:51Speaker 02

  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.

• 13:01Speaker 06

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

• 13:05Speaker 02

  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.

• 13:18Speaker 06

  There isn't much to generate revenue on the reservation.

• 13:23Speaker 06

  And ranching is one of those things that we can do, and it limits us on that.

• 13:30Speaker 02

  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-free introduction 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.

• 13:53Speaker 03

  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.

• 14:08Speaker 02

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

• 14:15Speaker 03

  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.

• 14:29Emily Kwong?

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

• 14:35Speaker 02

  You're welcome.

• 14:39Emily 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 Short Wave from NPR.

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