Fear itself enough to control mammal populations, study suggests

UVic study could offer hope for those who want to see the region’s deer population controlled without resorting to a cull.

A University of Victoria study could offer hope for those who want to see the region’s deer population controlled without resorting to a cull.

Predators lower the population of their prey, not just by killing them, but by scaring them as well.

It’s a conclusion made by a team of researchers who believe behavioural research collected on song sparrows in the Gulf Islands could be applied to predator-prey interactions of all kinds and used to manage their populations.

“The fear of falling victim to a predator can also have significant effects and affect the number of babies you have,” said Michael Clinchy, adjunct professor at the UVic and co-author of the study. “This can be as important as direct killing in reducing prey numbers.”

Over the past 10 summers, Clinchy, along with University of Western Ontario biologist Liana Zanette and UVic grad students, used electric fencing and fish-netting to fully protect sparrow nests from natural predators such as owls and raccoons on Portland Island and surrounding Gulf Islands. Through speakers hung in surrounding trees, one group of birds were subjected to recorded predator calls and sounds, while sounds of non-predatory animals such as geese played for a second group of song sparrows.

Clinchy and Zanette observed the birds via video and learned those exposed to predator sounds produced 40 per cent less offspring than the control group. These birds also spent more time guarding their nests and less time feeding their young, which also reduced their numbers.

“It’s the first time in any study of wild bird or mammal that fear alone has been shown to unambiguously affect birth and survival and thus the individuals in wildlife interactions,” Clinchy said. “Basically we think that this kind of fear effect is going to be pervasive on wildlife.”

Clinchy links his work to the management of elk populations in the American Yellowstone National Park and doesn’t overrule the possibility of controlling deer in Greater Victoria using the same principal. When wolves were reintroduced to the park in the mid-90s, the elk population decreased by 50 per cent – a reduction far greater than what the wolves were capable of killing, Clinchy said.

“It’s the fear itself that’s really responsible,” he said. “If you can simulate that, you could have effects in reducing the deer population.”

The study, Perceived Predation Risk Reduces the Number of Offspring Songbirds Produce per Year, was published in the December issue of Science magazine.

nnorth@saanichnews.com