The history of the Yellowstone wolf population is one of the most interesting conservation stories in the United States. In the course of 150 years, the wolf population in the Greater Yellowstone ecosystem went from being hunted almost to local extinction to a thriving population with up to nine different packs calling Yellowstone National Park home.
The Yellowstone wolves provide a classic example of how animal species are interconnected and the surprising fragility of large and seemingly robust ecosystems.
Keep reading to learn about the different types of wolves that call Yellowstone home and the many ways the rest of the ecosystem depends on them.
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Wolf Species Living in Yellowstone
The gray wolf historically called Yellowstone home and can be found there today after reintroduction efforts. Gray wolves are said to look like large German Shepherds. Their coat colors range between gray, brown, and black, with lighter fur on their faces, legs, and belly. Gray wolves have long, bushy tails that are often black-tipped.
Gray wolves are 26 to 36 inches (66.04 cm to 91.44 cm) tall at the shoulder and four to six feet (1.21 m to 1.82 m) long from nose to tail tip. Male and female gray wolves look fairly similar, with males being about fifteen to twenty percent larger than females. Male gray wolves weigh up to 130 pounds (58.96 kg) and female gray wolves weigh up to 110 pounds (49.89 kg).
Gray wolves can be both black and gray, with about an even distribution of the two colors found within the packs in Yellowstone
Life Cycle of Gray Wolves
Gray wolves have a lifespan of eight to ten years inside Yellowstone National Park and four to five years in the wild. All wolf species are usually monogamous and mate for life. Gray wolves mate in February and give birth in April. The average litter size is five pups.
Wolves live in packs and have layers of social behavior and hierarchy built into their pack structure. Most packs include an alpha male and female, with several subordinate wolves. Ten wolves is the average pack size for wolves in Yellowstone.
The leading cause of death for wolves inside Yellowstone National Park is other wolves, mostly from other packs. Human contact is the leading cause of death for wolves outside the park, from hunting and other conflicts with people outside of the national park boundaries.
Habitat and Range of Gray Wolves
Gray wolves can live in a wide range of habitats, including tundra, forests and grasslands. The historic range of gray wolves covered over half of the United States and reached from Canada to Mexico. The current range is much more limited, with gray wolf populations found in Alaska, the northern parts of Michigan, Wisconsin, and Minnesota, and parts of Montana, Idaho, Wyoming, and Oregon.
Wolves are carnivores. By working as a pack, the gray wolves in Yellowstone are able to hunt large prey that other predators in the area are unable to hunt. In the winter, elk make up about 90% of the Yellowstone wolves’ diets. In the summer, wolves are also likely to hunt deer and bison. Gray wolves will also act as scavengers when necessary, stealing and eating game killed by other carnivores.
Almost all the wolf populations in the US were gone by the 1920’s, hunted by ranchers protecting their wildlife and impacted by habitat loss as towns grew in their historic range, causing an increase of human/wildlife conflicts.
Wolf eradication in the United States was one of the most intense and successful wildlife removal programs undertaken in the country’s history. According to records, the last wolf shot inside Yellowstone National Park was killed in 1926.
The gray wolves of Yellowstone are the apex predator in their ecosystem, meaning they aren’t hunted by other predators and have access to whatever prey species are most abundant at the time. While their diet usually consists of large hooved animals, Yellowstone’s gray wolves will also eat rabbits, weasels, badgers, foxes, and other small mammals.
Wolf Wildlife Management History in Yellowstone
The environmental movement grew in the United States in the 1960s and 1970s, leading to passage of many laws designed to correct the population management mistakes made in the past in favor of restoring ecosystems to their natural state when possible.
The Endangered Species Act of 1973 was especially important. This act not only protected species currently in trouble but also recommended the restoration of native species if possible to restore the health of ecosystems. By 1978 all gray wolf subspecies were listed as federally endangered in all states except Minnesota and Alaska.
Scientists had almost seventy years to observe the Greater Yellowstone ecosystem and note important changes to ecosystem services and the dynamics of other plant and animal species without wolves. Realizing that wolf populations were an irreplaceable piece of the ecosystems, they began the process of reintroducing wolves to the Greater Yellowstone Ecosystem and started the reintroduction program in 1995.
The 1995 reintroduction efforts were controversial. Farmers, ranchers, and hunters in the area didn’t want wolves brought back to the area because of perceived impacts to livestock like sheep and cows. There were concerns that any wolves brought to the park would quickly move outside the park boundary and come into closer contact with people and livestock or return to where they came from.
Scientists were unsure how much of the ecosystem had been impacted by the wolf population and were unable to anticipate the full depth of the importance the wolf population had on the Greater Yellowstone Ecosystem.
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Wolves Reintroduced to Yellowstone
In January of 1995, eight gray wolves were captured in Jasper National Park in Alberta, Canada, and brought to Yellowstone National Park. Scientists continued to reintroduce gray wolves by bringing small packs to Yellowstone from other areas with healthy wolf populations, with a total of thirty-one wolves relocated to Yellowstone by the end of 1996.
Since wolf packs cover large areas and have a strong homing instinct, scientists were concerned the relocated wolves would simply head back to their homes in Canada. To make the transition more effective, three acclimation pens were built to house the wolves for several weeks. Elk carcasses were also placed in the new environment so the wolves would get an idea of what their new environment could provide: ample prey and lots of room to roam without needing to leave the Greater Yellowstone ecosystem.
Scientists also took steps to ensure the reintroduced wolves would not become acclimated to human presence during the reintroduction process. While the wolves had to come in contact with people to be captured and transported, contact was minimal once they were placed in the acclimation pens.
Even though the wolves were brought food and monitored for health, action was taken to limit their interactions with people during these times. The reintroduction was successful in minimizing habituation to people and the wolves avoided human contact when they were released from the acclimation pens.
As expected, one alpha male immediately headed north out of the park boundaries when released. The pregnant alpha female of the same pack followed. The male was shot soon after leaving the protected boundaries of the park, but the female was recovered and brought back to Yellowstone. Her pups were born successfully and many of the wolves currently found in the Greater Yellowstone Ecosystem can be genetically linked to the first wolves brought back to Yellowstone in 1995.
The full depth of the impact wolf populations have on the Greater Yellowstone ecosystem was unknown at the time of their removal and reintroduction to the park. The reintroduction program provided a unique opportunity for scientists to observe the changes that occur when a keystone species is brought back to an area after being gone for such a long time.
Even without knowing the full extent of their importance, scientists could see the ecosystem wasn’t functioning well and that an important species was missing. Since wolves were removed with such prejudice at the beginning of the 20th century, that was the first species to start with to improve the health of the ecosystem.
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Why Wolves are Important in Yellowstone
In the Yellowstone ecosystem, wolves are a keystone species. This means the rest of the ecosystem functions at a lower level when wolves aren’t present. Their keystone species status was unknown when wolves were removed from Yellowstone, as that pursuit was done in the name of human/wildlife conflict without regard to the health of the overall ecosystem.
The presence or absence of wolves in the Greater Yellowstone Ecosystem causes a trophic cascade. Trophic cascades describe the relationship apex predators have with their prey, and the relationship their prey have with their food sources. When apex predators limit the density or change the behavior of their prey, the food source of their prey changes as well. The Greater Yellowstone ecosystem’s trophic cascade directly impacted wolves, elk, and the plant species the elk eat. It also indirectly impacted beavers, scavenger species like ravens and magpies, and even the plant and fish species that rely on Yellowstone’s winding streams.
Without wolves, the elk population isn’t naturally managed. This causes overgrazing that impacts the health of other herbivore species in the area. The elk population in Yellowstone can quickly reach the ecosystem’s carrying capacity when not managed by wolves. The carrying capacity describes the size of a population the ecosystem can support. When elk exceeded the carrying capacity of Yellowstone, their regular food sources weren’t enough and elk had to expand their diet to include young willow, aspen, and cottonwood in the winter. The elk population also didn’t have to move as much during the winter because they weren’t under threat by wolves.
As elk ate more willow in one area during the winter without moving, beaver populations were impacted. Beavers need young willows to survive through the winter. The combination of year-round grazing on willow stands beside rivers and the absence of beaver populations actually straightened the streams that run through Yellowstone, changing the riverine ecosystems.
When wolves hunt and kill elk, they’re also providing food for ravens, magpies, coyotes, and even bears. Without wolves, the scavenger species like ravens and magpies had fewer food sources. While coyotes and bears do hunt on their own, they lack the pack dynamics that allow wolves to bring down larger prey like elk and bison. Coyotes and bears rarely take down elk on their own, which means wolves are the only species that naturally control the elk population.
In the twenty-five years that have passed since the 1995 reintroduction program, expected and unexpected changes have been observed in the Greater Yellowstone Area. Elk populations are once again under control, with the overall population breaking into smaller groups that stay on the move throughout the winter to avoid conflicts with wolf packs.
Willow stands along streams have healthier and more robust biomass, stabilizing the stream banks and providing resources for beavers. Beaver populations are slowly returning to the park and the streams are becoming winding and meandering once again. This is only the beginning of changes that will be observed in the Greater Yellowstone Ecosystem as the wolf population continues to become established and create a positive trophic cascade, restoring the health of the ecosystem in surprising ways.
It takes time to fully understand the dynamics of an ecosystem and be able to recognize the keystone species and anticipate all of the impacts they have at trophic levels beyond just their prey populations. Only five or six other similar reintroductions have been documented, making the Yellowstone wolf reintroduction a classic conservation success story.
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Wolf Populations in Yellowstone
At least 123 wolves live inside Yellowstone National Park as of January 2021, with nine individual packs noted. An estimated 528 wolves live in the Greater Yellowstone Ecosystem as of 2015. Wolf population levels inside the park have fluctuated between 83 and 123 since 2009. Monitoring of the wolf population in the Greater Yellowstone Area is managed by the Yellowstone Wolf Project and the Northern Rocky Mountain Wolf Recovery Plan.
Wolf Hunting Regulations Outside Yellowstone National Park
While hunting is prohibited inside Yellowstone National Park, wolves have large territories and reside in the Greater Yellowstone area, not just inside park boundaries. When wolves leave park boundaries, hunting regulations are subject to the state they are in. The wolf populations in the Greater Yellowstone Ecosystem have rebounded so well that they’re no longer on state or federal endangered species lists, but that does open the populations up to hunting as the state management agencies see fit.
These regulations change year-to-year depending on the wolf populations throughout the state as a whole and are managed by Montana Fish, Wildlife and Parks, Wyoming Game and Fish, and Idaho Fish and Game.
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Threats from Habitat Loss and Climate Change
Wolf populations have faced threats from habitat loss since westward expansion in the United States began. As land was converted for agriculture, natural prey species became less abundant and wolves had to adapt to using livestock species as prey or leaving the area.
Habitat loss caused by the introduction of agriculture was more intense in the 1800’s and 1900’s, but still happens at a lower level today.
Wolf packs can cover large territories and are currently threatened by habitat fragmentation. New roadways are especially challenging. As it becomes unsafe to cross interstates and highways, wolf territories become smaller and it becomes more challenging to hunt enough prey to continue to support the pack.
At this point it’s unclear how the Yellowstone gray wolves will be impacted by climate change. Gray wolves adapt easily to different types of habitats, making changes in precipitation, temperature, and snowpack less extreme for gray wolves. However, their prey species may be more susceptible to changes caused by climate change.
Cultural Myths and Legends Associated with Gray Wolves
Like many predators, wolves are subject to the perceptions of the people around them. Wolves are often featured in Native American mythology and legends as representations of courage, loyalty, and strength.
As settlers of European descent came into contact with wolves during westward expansion, the wolves were perceived as a dangerous presence to people and livestock and actions were taken to remove them from newly settled areas.
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