Imagine being a cougar in Yellowstone National Park in the northern USA. Until the mid-1990s, you were the area’s top predator and could take down the abundant elk – herbivores very closely related to European red deer – almost at will.
Then something changed. Wolves were reintroduced and have slowly increased in number.
Over time, the cougars found that they might go to the energy expense and danger of bringing down a massive elk – an adult can weigh anything from 200 to 500kg – and then face losing it to a bunch of the newcomers.
Because, even though a cougar (especially a male) is usually bigger than a grey wolf, it can’t compete with another carnivore that goes around in packs of up to 10 animals.
According to new research published by scientists from Oregon State University, the cougars now avoid those areas where wolves make their kills and stay closer to trees they can climb as a means of escape if necessary.
And instead of trying to compete with wolves for the declining number of elk, they have switched their attention to smaller prey – mule and white-tailed deer.
Comparing data for cougar kills between 1998 and 2005 with those made between 2016 and 2024, the researchers found the ratio of elk in their diet dropped from 80 to 52 per cent, while deer predation increased from 15 to 42 per cent.
Lead researcher Wesley Binder doesn’t think cougars understand there is a greater risk to themselves or that they may risk losing their meal if they take elk because of the presence of wolves in the park.
“We do not think cougars are able to connect the dots and instead hunt what is available,” he says. “We see variation in prey selection based on the age and size of the cougar – younger and smaller females tend to hunt more deer, while older, larger males hunt more elk.”
Binder says it’s important to understand how two top predators can affect each other’s behaviour and that the coexistence of wolves and cougars depends on prey diversity as much as prey abundance.
After heavy persecution of both species in the first half of the 20th century, cougar populations began to rebound in the 1960s and 70s, followed by wolves at least two decades later.
This research, says Binder, will give wildlife managers in other parts of North America an idea of what to expect where both species are returning to ecosystems. It suggests the impact may not be additive on prey because cougars can switch what they hunt.
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The study was published in the journal PNAS | Top image credit: Oregon State University
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