To a lot of people, coming across a wild cougar in your backyard might be pretty scary. But humans are the ultimate predators, nay, the super predators of the animal kingdom, striking fear in the hearts of even the most fearsome beasts, including cougars—and that could actually have important consequences all through the food chain.
A study released today in the Proceedings of the Royal Society B found that large carnivores, specifically cougars in rural and suburban areas near Santa Cruz, California, often drop everything that they're doing when they hear humans chit-chatting nearby, even running away halfway through a meal. "This has measurable consequences on the cougar's feeding behaviour," said co-author Liana Zanette of Western University. "Being fearful is having a negative effect on these animals' ability to feed themselves."
All video courtesy Liana Zanette
In the study, researchers set up automated speakers and cameras near a cougar's prey kill site. When the cougars were feeding, researchers played a sound—either a control noise of something they might normally hear (in this case frogs), or humans talking.
When the cougars heard human voices, they often literally dropped what they were doing and bolted. Then they either did not return to the site or took longer to do so, and over 24 hours, spent less than half as long feeding as when they were exposed to the frog sounds.
Zanette and the team deduced that because of this, large carnivores are taking in fewer calories when they perceive humans to be around. This doesn't just impact the cougars, but also smaller creatures that make up their diet: Larger carnivores would have to kill more prey when they are more frequently frightened by the human 'super predator,' which would have cascading effects through the food web. Large carnivores literally shape ecosystems, Zanette said.
"Globally we know that humans kill large carnivores about nine times the rate at which they would be killed naturally," she told me over the phone. "We're completely off the scale in terms of the threat that we represent to these animals. We're the super predator."
With humans encroaching on territories traditionally occupied by wildlife, including cougars, we could be inadvertently putting them—and other species—at risk.
"Landscapes are increasingly human dominated," Zanette said. "Large carnivores now have to coexist [with us] and evidently this is not a comfortable fit for them."
The exact impact of their fear of humans on the entire ecosystem still needs more study, she said, but for now it looks like the mere sound of human voices in conversation is spoiling these cougars' all-important meals.
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