American Scientist

YELLOWSTONE WOLVES: Science and Discovery in the World’s First National Park. Douglas W. Smith, Daniel R. Stahler, and Daniel R. MacNulty, eds. With a foreword by Jane Goodall. xvii + 339 pp. University of Chicago Press, 2020. Cloth, $35; ebook, $34.99.

The reintroduction of wolves to Yellowstone National Park in 1995 changed the park, in some cases in ways that had not been predicted. The essays collected in Yellowstone Wolves: Science and Discovery in the World’s First National Park discuss what scientists have learned from the park’s wolves since the reintroduction. The book’s contributors, who include many top wolf biologists, have compelling and inspiring stories to tell about conducting science in a special place.

A government program to eliminate wolves from the park began in 1914, and by 1926 they were gone. More than half a century later, a growing understanding of the ecological significance of wolves eventually led the government to decide to reintroduce them. So as editors Douglas W. Smith, Daniel R. Stahler, and Daniel R. MacNulty note in the preface to Yellowstone Wolves, the book is “a story about a change of heart.” They brought together this handsome, oversize volume to communicate the benefits this change of heart has had at Yellowstone. They also hope to change hearts elsewhere: One of their goals in creating the book was to promote better coexistence between humans and wolves. To that end, they have included multiple perspectives and have aimed to make the material accessible to a wide audience.

The book’s 19 chapters, most of which report detailed research results, are illustrated with dramatic photos and attractive graphics. Many chapters are also supplemented by one or more text boxes containing an essay, usually by someone who was not a chapter author. In addition, each of the book’s six parts (which are devoted respectively to history, behavioral and population ecology, genetics and disease, predation, ecosystem effects, and management) concludes with a guest essay about why Yellowstone wolves are important. There are a total of 79 contributors. Despite the variety of voices included, this volume has a consistent style and exceptional coherence for an edited volume. That coherence did not come about by coincidence: Eighteen chapters list at least one of the editors as a coauthor.

A note at the beginning of the book, right before the foreword by Jane Goodall, explains that an hour-long video containing interviews with some of the authors and footage of park wildlife, shot by filmmaker Robert K. Landis, is available as the last item listed here (press.uchicago.edu/sites/yellowstonewolves/); a username (yellowstone) and password (wolves2020) are needed to access the webpage. (If you own the ebook, the videos are embedded in the text.) If you don't have time to watch the hour-long video, you can view a small sample of Landis's good-quality footage of wolves in the park in a short trailer for the book.

The book’s first chapter provides historical and ecological context, showing the reader what the ecosystem of the area was like in three eras: before the park was established, during the early years of the park, and during the period when no wolves were present. The second chapter explains how the wolves returned. There were many political obstacles to their reintroduction. Even after the wolves had been captured and moved to Yellowstone—a logistically difficult endeavor—a court challenge kept them in their travel containers for 48 hours after they had arrived at the large outdoor pens in which they would be held for the first few months they were in Yellowstone.

Because the reintroduced wolves came from populations that had been persecuted by humans, it was assumed they would be shy and reclusive. To everyone’s surprise and delight, this turned out not to be the case, changing what was possible for scientists and for the public. Being able to repeatedly observe individual wolves led to a richer understanding of how they live. This special feature of the Yellowstone study comes through in a guest essay in which Olof Liberg notes that he had more spontaneous interactions with wolves in the three days he spent on horseback in Yellowstone than in his entire previous career as a carnivore biologist in Scandinavia. Similarly, Robert Hayes, who had spent nearly two decades as the Yukon wolf biologist, reports that he saw more wolves from a car in one day in Yellowstone than he had seen from the ground in his entire life before that point.

When the wolves were reintroduced, they were as free from disease as veterinary care could make them. Nonetheless, diseases had notable impacts within a few years. For example, distemper caused heavy mortality. Even though the wolf population is likely too small to maintain distemper, other carnivores in the park are reservoirs for it. Mange also kills wolves in Yellowstone. It was introduced into the ecosystem in the early 1900s, when some 200 coyotes were deliberately infected and released to spread the disease. Wolves were extirpated and reintroduced, and mange remains. The book does not explore disease spillover from domestic dogs; wolves would be far more likely to cross paths with dogs outside Yellowstone than within it.

After presenting wolves first as social animals with rich lives, and then as victims of disease, the editors bring predator-prey interactions into focus in the middle of the book. Wolves are adaptable and capable predators, but individual wolves are not built for capturing large prey. Only by working together can they capture elk, and large groups of them are needed to capture moose or bison. Even while working together, wolves mostly kill young, old, injured, or otherwise vulnerable ungulates. Many factors can make an animal vulnerable. For instance, after male elk drop their antlers, wolves are more likely to hunt and kill them.

Based on research that had been done elsewhere, scientists predicted that the reintroduction of wolves into Yellowstone would decrease elk numbers by perhaps 30 percent. However, the number of elk in the northern ranges of the Yellowstone ecosystem actually declined by about 75 percent from its peak before the arrival of wolves. Determining cause and effect is difficult, but the change in elk numbers is unlikely to be due solely to hunting by wolves, because a substantial drop in the elk population occurred during the wolves’ first winter in Yellowstone, when they were still being held in pens. Hunters and other predators have played a role in the decline: Many elk move outside the park seasonally and face hunting by humans, and grizzly bear and cougar populations have increased. Elk calves die at a far higher rate when more wolves and bears are present, although wolves are not usually the final cause of these deaths.

Since wolves have been reintroduced, the “new normal” number of elk in Yellowstone is similar to what it was when their herds underwent intense culling in the 1970s. But the impacts of the elk are different: Winter browsing by elk in the park has been greatly reduced, because a greater proportion of elk now winter outside the boundaries of the park. After the number of elk had been reduced by shooting in the park, and before the wolves were brought back, there was a period during which elk were shot outside the park in winter but faced few predators inside the park. During this period, many elk began spending the winter in the park and grazed on the trees there; as a result, few trees were able to grow up past bite height.

Across much of the potential range of wolves, wolf population density has been set by human action. Even where wolves have “recovered,” their lives are often cut short by bullets, vehicles, and other human-associated causes. Yellowstone is our best-documented example of letting wolves set their own limits. After their reintroduction, wolf densities in Yellowstone increased, with wolves in the northern range reaching some of the highest densities known anywhere, but the number of wolves has declined over the past several years. As of this writing, Yellowstone seems to have settled into an equilibrium; roughly 100 wolves are present, and they travel in about 10 packs. Data from Yellowstone suggest that adult mortality is a key predictor of wolf density. The authors suggest that territorial aggression by rival wolfpacks results in the kind of adult mortality that limits wolf density, and that wolves could sustain higher densities if they hunted across the landscape rather than dividing it up into large territories. Although three outbreaks of distemper decreased the number of wolves in Yellowstone during the first 25 years following reintroduction, those dips in population are seen as having been temporary deviations from longer-term limits believed to be enforced by the social behavior of the wolves.

The restoration of wolves to Yellowstone has allowed us to see how wolves can live within the fullest assemblage of large mammals left in North America. Now that Yellowstone has wolves again, it also has more cougars, grizzly bears, bison, pronghorn, and beavers. Coyotes persist, even though they are persecuted by the wolves. Scavenging allows predators to make it through times when hunting is bad. A bison or moose carcass can make a real difference to a pack of wolves down on their luck. Also, scavenging from wolf kills provides a steady subsidy to smaller animals, because wolves hunt in all years and all months—unlike humans and bears.

Results of studies from Yellowstone and elsewhere suggest that we should expect wolves to have ecological impacts beyond their consumption of and direct competition with a few species. Although we should expect indirect effects of wolves to ripple through ecological webs, we also should expect surprises. The ripples may be different in locations that lack the full complement of elk, moose, bison, grizzly bears, and pumas present in the Yellowstone ecosystem.

The last section of the book examines interactions of wolves with humans. Yellowstone is a shining example of coexistence based on mutual respect. Park rangers watch for any wolves who get too comfortable around people and cars, and they insist that park visitors not intrude on or block the paths of wolves.

The final full chapter looks for a way forward for wolves that live partly in the park and partly in surrounding areas. Although only a handful of wolves are shot each year, the packs from which they come are less likely to persist and raise pups afterward. This chapter recommends limiting “harvest” in “management units” adjacent to the park. The rhetoric of this recommendation contrasts with that of a statement that follows in the afterword: “There is a space in which humans and wolves can live together, and wolves in Yellowstone, in the past 25 years, have asked us to create that space—not just within the park, but beyond.” Outside Yellowstone, the assumption is that humans choose the number of wolves. Though hearts may have changed, our systems of discourse and practice remain biased toward excluding wolves. This volume does not suggest how to proceed outside the greater Yellowstone ecosystem, but it richly documents the rewards that have flowed from sharing this part of the world with wolves.

A graphic in the afterword summarizes the activities of the Yellowstone Wolf Project from 1995 through 2018. I was impressed by the many scientific publications (85) and conference presentations (45) that resulted from the project, and my jaw dropped when I saw that 1,915 interviews were conducted and that another 4,305 formal presentations and 14,767 informal presentations were made. I suspect that much of the book’s narrative was developed before live audiences.

I recommend this collection highly; it is full of important stories told well.