How Wolves and Cougars Share Yellowstone National Park

New research following wolves and cougars for almost a decade reveals how these competing predators share Yellowstone National Park, alter their diets and transform one of North America’s most familiar ecosystems.

A park where major predators returned

Yellowstone National Park has become an unusual real-world laboratory for studying large carnivores. Throughout much of the 20th century, hunting and government predator-control programmes had almost eliminated wolves and cougars from the western US. Greater protection enabled cougars to begin returning during the 1960s. Wolves were intentionally restored to Yellowstone in the mid-1990s, a decision that remains politically controversial outside the park.

Both animals now range across many of the same valleys and ridgelines. Their shared territory led scientists to examine an important question: can two formidable predators that both hunt hoofed animals, including elk, coexist without one forcing the other out?

Yellowstone now hosts the full cast of large carnivores that once roamed much of North America, from wolves and cougars to grizzly bears.

Researchers addressed this question by pairing nine years of GPS collar records with field examinations of nearly 4,000 feeding and kill sites throughout the park. Published in the journal PNAS, their work offers a detailed view of an ecosystem that is continuing to establish a new equilibrium.

Unequal competitors: why wolves dominate cougars

An adult cougar may weigh as much as a wolf, but body size is not what determines the relationship between them. Wolves act in coordinated packs, whereas cougars hunt and feed alone.

The findings showed a marked imbalance. Wolves occasionally kill cougars and often take over their kills, while cougars do not kill wolves. The researchers describe these encounters as “very one-sided”.

This result supports previous observations indicating that wolves generally occupy the highest position in the carnivore hierarchy where the species overlap. A pack can intimidate a solitary cougar and drive it away from a carcass with minimal danger to itself.

Wolves’ strength lies in the pack, allowing them to dominate solitary cougars and control access to large carcasses.

How changing food choices alter conflict

The Yellowstone story takes a new turn with shifts in the predators’ diets. Elk, formerly the principal prey of both species, have become less common across the park since the late 1990s. The research identified a clear change:

• Elk in wolf diets dropped from about 95% to 64% between 1998 and 2024.
• Elk in cougar diets dropped from about 80% to 53% over the same period.

The reduction led the two predators to adapt differently. Wolves began killing more bison, Yellowstone’s largest hoofed animal, while cougars increasingly preyed on smaller animals such as deer.

This change also affected the frequency of encounters. After killing an elk, cougars required more time to feed and could return to the carcass over several days. Wolf packs therefore had time to find the kill, scavenge it or displace the cougar. Encounters were about six times more likely when a cougar had killed an elk instead of a deer, the study found.

By targeting smaller, faster-to-eat prey, cougars reduced the window of opportunity for wolves to steal from them or launch attacks.

Put simply, the decline in elk produced fewer large and obvious cougar kills, reducing potentially dangerous contact with wolves. This ability to adjust their diet appears to be a central reason cougars can coexist with their more dominant competitors.

Landscape as protection: how terrain influences predator encounters

Diet is not the only factor shaping the balance between wolves and cougars. The physical landscape matters too. Yellowstone contains a wide range of environments, including expansive open valleys, dense woodland, steep canyons and rocky cliffs.

When the researchers connected GPS movements with terrain maps, they found that cougars did better in wooded or rugged places. Trees, uneven ground and steep slopes provide “escape terrain”, allowing a cougar to climb, conceal itself or move through landscapes that hinder wolf packs.

Rugged, forested ground acts as a natural refuge for cougars, limiting dangerous contact with wolf packs.

In open areas, wolves’ advantages of speed, stamina and cooperative tactics are more decisive. Consequently, the two species use the park’s terrain in slightly different ways, despite occupying the same broad areas.

Conditions that support uneasy coexistence

The study indicates that coexistence among large predators is most secure when three factors combine:

Yellowstone currently provides this combination. Wolves and cougars both maintain stable populations, even while continuing to alter one another’s behaviour and influence the broader ecosystem.

Ripple effects through the Yellowstone food web

Interactions between predators affect far more than the predators themselves. As wolves take more bison and fewer elk, and cougars partly shift from elk to deer, the consequences spread through vegetation and smaller carnivores.

In some locations, fewer elk may lessen browsing of young shrubs and trees, with implications for beavers and songbirds that depend on woody plants. Changing deer predation can affect how deer use particular valleys and woodland edges. Partly consumed carcasses left by wolves or cougars also provide food for scavengers, including coyotes, foxes, ravens and bears.

Predator clashes echo through the food chain, changing not just who gets eaten, but where plants grow and which scavengers thrive.

Scientists are still working through these indirect effects. An important question is whether several large carnivores “stack” their effects on prey populations, or whether interactions between the predators offset some of those impacts. Yellowstone, still adapting after decades without wolves, provides a rare opportunity to observe this process as it happens.

Key ecological terms behind the headlines

Several ecological ideas underpin the Yellowstone story and help clarify these patterns:

• Ungulates: Hoofed mammals such as elk, deer and bison. They form the main prey base for many large carnivores.
• Scavenging: Eating animals killed by another predator. Wolves often scavenge cougar kills, reducing the return the cats receive from hunting.
• Intraguild competition: Competition between species that eat similar prey and might, in principle, prey on one another.
• Escape terrain: Features of the landscape that benefit prey or subordinate predators, including cliffs, thick forest and rocky outcrops.

These concepts feature repeatedly in research into predator coexistence, whether it concerns North American wolves and cougars, African lions and hyenas, or wild dogs and leopards.

What Yellowstone can show other regions

As wolf and cougar ranges expand across the western US, disputes involving livestock and hunters remain politically sensitive. Yellowstone offers lessons for land managers beyond its boundaries.

A varied prey base seems to reduce competition between predators by giving them alternatives to livestock. Conserving or restoring habitats with cover and rugged escape terrain may likewise limit risky encounters, both between predators and between carnivores and people. Tensions are more likely to intensify where carnivores are confined to simplified, heavily grazed landscapes containing only one main prey species.

Ecologists increasingly use computer models to explore “what if” scenarios, such as further elk declines or rising wolf numbers alongside falling cougar populations. Such simulations can help predict where conflicts, either between predators or with people, are most likely to develop before they become evident on the ground.

For people walking Yellowstone’s trails, this research is a subtle reminder that distant howls and unseen pawprints belong to an ecosystem still adapting after a century of absence. Wolves and cougars have returned, but their shared story in this landscape continues to unfold, one carcass and one GPS ping at a time.