New research tracking wolves and cougars over nearly a decade shows how these rivals manage to share the same park, shift their diets and reshape one of North America’s best-known ecosystems.
A park where predators made a comeback
Yellowstone National Park has become a rare living laboratory for large carnivores. For much of the 20th century, wolves and cougars were nearly wiped out in the US west, largely due to hunting and government predator-control programmes. Cougars began creeping back under stronger protections in the 1960s. Wolves were deliberately reintroduced to Yellowstone in the mid-1990s, a move that remains politically charged beyond the park’s borders.
Today, both species roam many of the same valleys and ridges. That overlap prompted scientists to ask a basic but urgent question: can two powerful predators, both targeting hoofed animals such as elk, live side by side without one driving out the other?
Yellowstone now hosts the full cast of large carnivores that once roamed much of North America, from wolves and cougars to grizzly bears.
To answer that, researchers combined nine years of GPS collar data with on-the-ground investigations of almost 4,000 kill and feeding sites across the park. Their study, published in the journal PNAS, paints a detailed picture of a system that is still settling into a new balance.
Unequal rivals: why wolves dominate cougars
Although an adult cougar can weigh as much as a wolf, size is not the deciding factor. Pack behaviour is. Wolves operate as coordinated groups, while cougars hunt and feed alone.
The data revealed a clear asymmetry: wolves sometimes kill cougars and frequently steal their kills. Cougars, by contrast, do not kill wolves. Encounters are “very one-sided”, the researchers report.
That pattern matches earlier observations suggesting that, where they overlap, wolves usually sit at the top of the carnivore hierarchy. A pack can harass and displace a solitary cat from a carcass with little risk.
Wolves’ strength lies in the pack, allowing them to dominate solitary cougars and control access to large carcasses.
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How food choices change the conflict
The new twist in the Yellowstone story comes from changing diets. Since the late 1990s, elk – once the main prey for both predators – have become less abundant across the park. The study tracked a clear shift:
- 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.
That decline pushed each predator along a different path. Wolves began taking more bison, the park’s largest hoofed animal. Cougars increasingly turned to smaller prey, such as deer.
That switch changed how often the two species clashed. When cougars killed elk, they needed longer to eat, sometimes returning to the carcass over days. That gave wolf packs time to locate the kill and either scavenge or force the cougar away. The study found that encounters were about six times more likely when cougars had killed elk rather than deer.
By targeting smaller, faster-to-eat prey, cougars reduced the window of opportunity for wolves to steal from them or launch attacks.
In short, fewer elk meant fewer large, conspicuous kills for cougars, which in turn cut down dangerous meetings with wolves. This dietary flexibility appears to be one of the main reasons cougars have been able to coexist with their more dominant rivals.
Landscape as a shield: how terrain shapes predator encounters
Food alone does not dictate the balance between wolves and cougars. The structure of the land itself also matters. Yellowstone is far from uniform. It includes broad open valleys, thick forests, steep canyons and rugged cliffs.
By linking GPS tracks with maps of terrain, the researchers found that cougars fared better in rough or forested areas. Steep slopes, broken ground and trees create “escape terrain” where a cat can climb, hide or navigate terrain that slows down packs of wolves.
Rugged, forested ground acts as a natural refuge for cougars, limiting dangerous contact with wolf packs.
In more open country, wolves’ strengths – speed, endurance and group tactics – dominate. That means the two predators tend to use the landscape in subtly different ways, even when they share the same broad region of the park.
Ideal conditions for uneasy coexistence
The study suggests that coexistence between large predators is most stable when three ingredients come together:
| Factor | Role in coexistence |
|---|---|
| Diverse prey | Allows each predator to adjust diets and reduce direct competition. |
| Varied terrain | Provides safe spaces for weaker or solitary species such as cougars. |
| Room for behavioural shifts | Lets predators alter hunting strategies as populations change. |
Yellowstone currently offers that mix. Both wolves and cougars have stable populations, even as they continue to reshape each other’s behaviour and the wider ecosystem.
Ripple effects across the Yellowstone food web
What happens between predators does not stay between predators. When wolves kill more bison and fewer elk, and cougars switch partly from elk to deer, those decisions cascade through vegetation and smaller carnivores.
Fewer elk in some areas can reduce browsing pressure on young trees and shrubs, affecting songbirds and beavers that rely on woody plants. Shifts in deer predation can alter how deer use certain valleys or forest edges. When wolves or cougars leave partially eaten carcasses, scavengers such as coyotes, foxes, ravens and even bears benefit.
Predator clashes echo through the food chain, changing not just who gets eaten, but where plants grow and which scavengers thrive.
Scientists are still untangling these knock-on effects. One key question is whether multiple large carnivores “stack” their impacts on prey populations, or whether their interactions cancel some of those effects out. The Yellowstone system, still adjusting after decades without wolves, offers a rare chance to watch that process play out in real time.
Key ecological terms behind the headlines
Several concepts sit quietly behind the Yellowstone story and help explain what is going on:
- Ungulates: Hoofed mammals such as elk, deer and bison. They form the core prey base for many large carnivores.
- Scavenging: Feeding on animals killed by others. Wolves frequently scavenge cougar kills, reducing the cats’ pay-off from hunting.
- Intraguild competition: Competition between species that both eat similar prey and could, in theory, prey on each other.
- Escape terrain: Landscape features that give prey or subordinate predators an advantage, such as cliffs, dense forests or rocky outcrops.
These ideas crop up repeatedly in studies of predator coexistence, whether the species involved are wolves and cougars in North America, lions and hyenas in Africa, or wild dogs and leopards.
What Yellowstone can teach other regions
As wolves and cougars expand across the western US, conflicts with livestock and hunters remain politically sensitive. The Yellowstone case offers some lessons for land managers working outside the park’s borders.
Diverse prey populations appear to soften competition between predators, giving them options besides livestock. Protecting or restoring habitat that provides cover and rugged escape terrain can also reduce risky encounters, both between predators and with people. Where carnivores are pushed into simplified, heavily grazed landscapes with only one main prey species, tensions are more likely to spike.
Ecologists are increasingly using computer models to test “what if” scenarios: what happens if elk decline further, or if wolf numbers rise while cougar numbers fall? These simulations can help anticipate where clashes – either between predators or with humans – are most likely, long before they show up on the ground.
For visitors walking Yellowstone’s trails, the science offers a quiet reminder: those distant howls and unseen pawprints mark a system still adjusting after a century of absence. Wolves and cougars have returned, but the story of how they share this landscape is still being written, one carcass and one GPS ping at a time.