Fear of Predation Affects Animal Populations

Just the fear of anticipated attack is enough to significantly affect wildlife population numbers, even when predators are prevented from directly killing any prey. That’s the conclusion of a new study conducted by a team of researchers that includes UVic adjunct biology professor Michael Clinchy.

The results confirm what scientists have been speculating for years—that wild animals, being in peril every moment of every day of being torn limb from limb by any number of predators, experience a condition similar to post-traumatic stress in humans and it affects their reproductive abilities.

“Our results suggest that the perception of predation risk is itself powerful enough to affect wildlife population dynamics and should be given greater consideration in vertebrate conservation and management,” says Clinchy.

He and lead study author Liana Zanette, a biologist at the University of Western Ontario, conducted their ground-breaking research on song sparrows nesting on Portland Island and several other small islands in BC’s southern Gulf Islands. They protected every nest with both electric fencing and seine (fish) netting, making is impossible for natural predators such as hawks and raccoons to attack. Cameras were trained on the nests 24/7 so the researchers were confident no eggs or nestlings were directly killed by predators during the observation period.

The researchers then played different sounds to different groups of birds throughout the four-month breeding season. One group heard sounds associated with their natural predators while the other heard non-threatening natural sounds.

“The birds that were hearing the predator sounds produced 40 per cent fewer offspring—simply due to the sound of fear—that’s a very significant decrease,” says Clinchy. “What this shows is that predators significantly affect the population sizes of their prey not just by killing prey but by scaring them as well.

“This has important implications for conservation and wildlife management because it suggests that the total impact of predators on prey populations will be underestimated if the effect of fear itself is not considered,” says Clinchy. “This means that the adverse effects of introduced predators are likely worse than previously imagined and the disturbance to native ecosystems due to the loss of native predators has probably been greater than we previously thought.”

The study, Perceived Predation Risk Reduces the Number of Offspring Songbirds Produce per Year, is published in the December issue of Science magazine. Research video and images, and copies of the study are available at http://communications.uwo.ca/media/populationfear/
 

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