The history of wolves in Yellowstone includes the removal, absence, and return of gray wolves (Canis lupus) to Yellowstone National Park and the Greater Yellowstone Ecosystem. When the park was established in 1872, wolf populations were already decreasing in Montana, Wyoming, and Idaho. The creation of the national park did not protect wolves or other predators, and government programs to control predators in the early 1900s helped remove gray wolves from Yellowstone. The last wolves in Yellowstone were killed in 1926. After that, occasional sightings of wolves were reported, but scientists confirmed in the mid-1900s that gray wolves had been completely removed and were not present in Yellowstone or any of the 48 states.

Starting in the 1950s, park managers, biologists, conservationists, and environmentalists began an effort to bring gray wolves back to Yellowstone National Park. When the Endangered Species Act of 1973 was passed, it became possible to legally reintroduce wolves. In 1995, gray wolves were brought back to Yellowstone in the Lamar Valley. The return of wolves to Yellowstone has been a topic of debate, as have similar efforts to reintroduce wolves in other areas worldwide.

Extirpation (1872–1926)

In 1872, when Yellowstone National Park was created, there were no laws to protect animals in the park. During the park’s early years, people in charge, hunters, and visitors could kill any animals they found. The gray wolf was especially at risk because people often saw it as a dangerous predator and were trying to remove it from areas where it lived to protect farm animals. In January 1883, the U.S. Secretary of the Interior, Henry M. Teller, made rules that banned hunting most animals in the park, but wolves, coyotes, bears, mountain lions, and other small predators were not included in these rules.

After the U.S. Army took control of the park on August 1, 1890, the first military leader, Captain Moose Harris, allowed hunting of all wildlife and let the park’s staff handle predator control. However, official records show that the U.S. Army did not begin killing wolves until 1914.

In 1885, Congress created the Division of Economic Ornithology and Mammalogy to study wildlife for protection. This group later became the U.S. Biological Survey, which eventually led to the creation of the U.S. Fish and Wildlife Service. In 1907, due to pressure from western cattle and livestock industries, the agency started a program to control predators, which later became known as Animal Damage Control. This program killed about 1,800 wolves and 23,000 coyotes in 39 U.S. National Forests in 1907 alone. When the National Park Service was created in 1916, its laws allowed the Secretary of the Interior to “destroy” animals or plants that harmed the use of parks, monuments, or reservations.

It is widely believed that gray wolf groups that could survive long-term were removed from Yellowstone National Park by 1926. The National Park Service continued its predator control policies until 1933. However, a study from 1975 to 1977 found that between 1927 and 1977, there were several hundred possible sightings of wolves in the park. From 1977 until wolves were reintroduced in 1995, there were more sightings, but most were likely single or paired wolves passing through the area, not living there permanently.

Before the National Park Service took over the park in 1916, the U.S. Army killed 14 wolves during their time in charge (1886–1916), mostly between 1914 and 1915. In 1940, Adolph Murie, a wildlife biologist, published a report titled Fauna of the National Parks of the United States—Ecology of the Coyote in the Yellowstone National Park. In this report, Murie listed the number of wolves killed each year by park staff from 1915 to 1935.

Research in the 1980s confirmed that the last official killing of wolves in the park happened in 1926, when two wolf pups near Soda Butte Creek were killed by park rangers. The last reported wolf killed in the Greater Yellowstone Ecosystem (before modern legal hunting or control measures) occurred in May 1943, when Leo Cottenoir, a Native American sheepherder on the Wind River Reservation, shot a wolf near the park’s southern border.

Absence (1926–1995)

After the wolves were removed from Yellowstone National Park, the number of elk increased. Over the next few years, the condition of the park worsened greatly. Scientists who visited Yellowstone in 1929 and 1933 described the land as being in very poor condition and noted that it was getting worse over time. By this time, many biologists were concerned about soil erosion and plants dying. The growing elk population inside the park caused overgrazing, which harmed trees like aspen and cottonwood. To address this, the park service began trapping and moving elk. When this did not work, they started killing elk. These efforts to control elk populations continued for more than 30 years. While these actions stopped the land from getting worse, they did not improve its condition. Some people suggested bringing wolves back to Yellowstone to help control the elk population. However, Yellowstone's managers were not interested in reintroducing wolves, especially since they had successfully removed them from the park before. Elk control continued into the 1960s. In the late 1960s, local hunters complained to their congressmen that there were not enough elk, and the congressmen threatened to stop funding Yellowstone. Killing elk as a control method was stopped, allowing elk numbers to rise again. As elk populations grew, the quality of the land worsened, harming many other animals. Without wolves, coyote numbers increased, which negatively affected pronghorn antelope populations. However, the overpopulation of elk had the greatest impact on Yellowstone's ecosystem in the absence of wolves.

Efforts to bring back gray wolves to Yellowstone began with important studies about predator-prey relationships in the park. In 1940, Adolph Murie published Ecology of the Coyote in the Yellowstone National Park, and his work The Wolves of Mount McKinley (1940–41) helped build scientific support for wolf conservation. In 1944, Aldo Leopold, a well-known wildlife biologist who once supported predator control, wrote a review of The Wolves of North America (Young and Goldman, 1944) that highlighted the importance of wolves.

By the 1960s, people's understanding of ecosystems changed, leading to more support for wolves and other large predators. This included the idea of a "keystone species," introduced by Robert Paine in the early 1960s. In the 1960s, Douglas Pimlott, a Canadian wildlife biologist, called for restoring wolves in the northern Rockies.

In 1970, David Mech, an American wolf expert, published The Wolf: The Ecology and Behavior of an Endangered Species, which explained how wolves affect their environment. In 1978, John Weaver, a wildlife biologist, wrote Wolves of Yellowstone and recommended reintroducing wolves to the park.

The gray wolf was listed as endangered in 1967 under the Endangered Species Preservation Act of 1966. However, the Endangered Species Act of 1973 was needed to legally reintroduce wolves to Yellowstone and the Greater Yellowstone Ecosystem. This law required the U.S. Fish and Wildlife Service to create recovery plans for endangered species. The first recovery plan was completed in 1980 but had little support. In 1987, the U.S. Fish and Wildlife Service published a revised Northern Rocky Mountain Wolf Recovery Plan, which involved cooperation between the National Park Service, Fish and Wildlife Service, universities, state wildlife agencies, and environmental groups. The plan's Executive Summary stated:

— Northern Rocky Mountain Wolf Recovery Plan, USFWS, August 1987

In 1991, Congress asked the U.S. Fish and Wildlife Service to create an Environmental Impact Statement (EIS) to reintroduce wolves to Yellowstone and Central Idaho. The final EIS, published on April 14, 1994, outlined five options for reintroducing wolves:

• Reintroduction of Experimental Populations (combining parts of the 1987 Recovery Plan and state-led efforts).
• Natural Recovery (with limited land-use rules to address potential illegal killing).
• No wolves (as proposed in the initial plan).
• Wolf Management Committee (as suggested by Congress).
• Reintroduction of Non-experimental Wolves (with fewer land-use restrictions).

The first option was chosen and implemented.

— EIS-The Reintroduction of Wolves to Yellowstone National Park and Central Idaho, 1994

The final EIS allowed the reintroduction to proceed, though some groups opposed it. The Sierra Club and National Audubon Society argued that experimental wolf populations needed more protection outside the park. The Farm Bureau of Idaho, Wyoming, and Montana objected to the choice of the northwestern wolf (Canis lupus occidentalis) instead of the Northern Rocky Mountains wolf (Canis lupus irremotus). These concerns were addressed, and in January 1995, the process of reintroducing wolves to Yellowstone began.

Reintroduction (1995–present)

In January 1995, U.S. and Canadian wildlife officials captured 14 wolves from several groups east of Jasper National Park, near Hinton, Alberta, Canada. These wolves were sent to Yellowstone in two groups—January 12, 1995 (8 wolves) and January 20, 1995 (6 wolves). They were placed in three temporary enclosures called acclimation pens—Crystal Creek, Rose Creek, and Soda Butte Creek in the Lamar Valley in the northeast part of Yellowstone National Park. In March 1995, the enclosures were opened, and all 14 wolves were released into the park between March 21 and March 31, 1995.

Seventeen more wolves captured in Canada arrived in Yellowstone in January 1996 and were released into the park in April 1996 from enclosures called Chief Joseph, Lone Star, Druid Peak, and Nez Perce. The reintroduction plan was expected to take 3–5 years, but these were the final wolves released because officials believed the wolf population was growing naturally.

Wolf population declines can happen because of fighting among wolves, not enough food, a skin disease called mange, a disease called canine distemper, hunting by people outside the park (for sport or to protect livestock), and in one case in 2009, park officials removed a wolf that had become used to humans.

Data from 1995 to 1999 shows the wolf population in the Greater Yellowstone Ecosystem. Since 2000, monitoring has focused on wolf packs inside the park. Wolves have spread to areas outside the park, and the last official count in 2002 showed 272 wolves in the region.

Scientists have studied the effects of wolves on Yellowstone’s ecosystem since their reintroduction in 1995.

As the wolf population grew, the elk population, which wolves hunt, decreased. Before wolves returned, experts predicted wolves would kill about 12 elk per wolf each year. However, wolves now kill an average of 22 elk per wolf annually. This decline in elk numbers has changed plant life, especially willows, cottonwoods, and aspens near heavily wooded areas. While wolf hunting directly causes elk deaths, research shows elk behavior has also changed. Wolves have forced elk to live in less ideal habitats, increased their stress, reduced their nutrition, and lowered their birth rates.

After wolves returned, they became major predators of coyotes. Between 1995 and 1996, the coyote population in Yellowstone changed greatly. Before wolves returned, Yellowstone had one of the largest and most stable coyote populations in the U.S. due to limited human interference. Two years after wolves were reintroduced, the coyote population dropped by 50% because of competition and wolves hunting coyotes. Coyote numbers were 39% lower in areas where wolves lived. In one study, about 16% of tracked coyotes were killed by wolves. Coyotes now live in steeper areas instead of open meadows. Carcasses in open areas no longer attract coyotes because wolves often kill them there. Coyotes feel safer on steep terrain, where they can lead wolves downhill. When wolves chase them, coyotes turn and run uphill. Wolves, being heavier, cannot stop, giving coyotes a chance to escape. While wolves usually dominate fights, coyotes sometimes attack wolves if they outnumber them. Both species may kill each other’s young if given the chance.

Coyotes naturally control fox populations, so the drop in coyotes led to more foxes. This change affects animals like hares, young deer, and small rodents and birds that foxes hunt. These changes influence how often certain plants are eaten, altering local plant communities and continuing down the food chain to fungi and microbes.

The return of wolves also helped the beaver population grow. In 2001, there was only one beaver colony in Yellowstone, but by 2011, there were nine. Wolves caused elk to move more widely, reducing pressure on willows, which beavers need to survive the winter. Beaver dams help the ecosystem by storing water, cooling streams for fish, and preventing erosion. They also create new habitats for animals like moose, otters, and birds.

Wolves also helped grizzly bears by increasing berry growth, a key food source for bears.

Wolf kills provide food for many animals, including ravens, wolverines, bald eagles, golden eagles, grizzly bears, black bears, jays, magpies, martens, and coyotes.

Wolf packs sometimes take kills made by cougars, pushing cougars back to mountain areas instead of valleys.

The reintroduction of wolves, an apex predator, caused a chain reaction in the ecosystem, known as a trophic cascade.

Because gray wolf populations in Montana, Wyoming, and Idaho had grown enough to meet recovery goals, the U.S. Fish and Wildlife Service changed the status of the Northern Rocky Mountain Distinct Population Segment from Endangered to Experimental Population-Non Essential on May 4, 2008. Wolves in Yellowstone and the Greater Yellowstone Ecosystem are part of this group. In response, Idaho and Montana set hunting limits for wolves under their state management plans. Environmental groups opposed the hunting seasons, but legal challenges failed, and hunts began in Montana in September 2009. Wolves inside the park remained fully protected, but wolves outside the park in Idaho or Montana could be legally hunted. During these hunts, Montana hunters killed wolves in the Absaroka-Beartooth Wilderness near the park’s northeast corner.

Reactions

From 2000 to 2004, the Montana Fish, Wildlife and Parks decreased antlerless permits by 51%, from 2,882 to 1,400. In 2006, they proposed only 100 permits, which was a 96% decrease from the 2,660 permits issued in 1995. At first, the impact of wolf predation on elk during the first five years of the recovery was not noticed, as elk numbers remained the same as those from 1980 to 1994. However, from the winter of 1995 to the winter of 2004, elk numbers dropped significantly, from 16,791 to 8,335. During this time, the number of wolves on the northern range increased from 21 to 106. Other factors, such as predation by bears, increased human hunting, harsher winters, and droughts, also contributed to the decline. Since 2000, 45% of known deaths and 75% of predation-caused deaths of radio-collared cow-elk have been confirmed to be caused by wolves. Human-caused deaths during the same period accounted for 8–30% of known deaths. Yellowstone elk make up to 92% of the winter diet of wolves. The estimated kill rate of Yellowstone wolves on elk during winter is 22 ungulates per wolf annually, which is higher than the 12 ungulates per wolf rate predicted in the ESA.

Historically, the wolves native to Yellowstone were classified as the subspecies C. l. irremotus. When the question of which subspecies to use for reintroduction was raised, U.S. Fish and Wildlife Service representatives explained that the taxonomy of gray wolves had changed many times and that C. l. irremotus was not a distinct subspecies but a geographical variant. Three publications discussed the suitability of using a founding population of Canadian wolves. Brewster and Fritz supported this idea, while Nowak concluded that the original Yellowstone wolves were more similar to C. l. nubilus, a subspecies already found in Minnesota, and that the proposed Canadian wolves were of the subspecies C. l. occidentalis, which is significantly larger. Brewster and Fritz argued that wolves have little genetic diversity and that the original population was already extinct. Nowak disagreed, stating that Minnesota wolves were more similar in size and shape to the original population than the proposed Canadian wolves, though he acknowledged that C. l. occidentalis may have been migrating south before human intervention. Doug Smith noted that the size difference between the introduced wolves and the original wolves was only about 6–7%, and that Minnesota wolves had no experience with elk and bison and were not adapted to mountainous terrain. Smith and Yellowstone National Park deny the claim that the "wrong wolf" was introduced.

In popular culture

The podcast Criminal discussed the killing of Wolf 10, a male, in their episode titled "Wolf 10." Another podcast, This is Love, created an episode about bringing wolves back to Yellowstone. This episode talked about the stories of Wolves 8 (male), 21 (male), and 42 (female).