How Barking Dogs Restored an Island Ravaged by Raccoons

Researchers broadcast the sound of predators to scare the voracious pests, allowing native wildlife to bounce back.
A raccoon on the Gulf Islands in British Columbia. (Photo: Western University)
Feb 24, 2016· 2 MIN READ
John R. Platt covers the environment, wildlife, and technology and for TakePart, Scientific American, Audubon, and other publications.

If you go camping on British Columbia’s Gulf Islands, keep a close eye on your food while you’re there.

“The raccoons here are quite bold,” said Justin Suraci, an ecologist with the Raincoast Conservation Foundation. “We’ve done a lot of camping while we were on the islands, and we had raccoons come right up to our campsite while we were sitting there, look us in the eye, and steal food right off of our picnic table.”

There’s a reason for that boldness: Raccoons don’t need to worry about becoming dinner themselves on the Gulf Islands. Humans killed off all the major predators a century ago. Now that there are no cougars, wolves, or bears to keep the raccoons in check, the masked marauders have run rampant.

They don’t stop at picnic tables: The raccoons eat everything they find, including songbirds, crabs, and fish. “They’re essentially out night and day, eating all the time, and having a pretty dramatic impact on the entire ecosystem,” Suraci said. The populations for many of the islands’ native species have declined by as much as 90 percent as a result.

A speaker that broadcast the sound of barking dogs to scare raccoons on the Gulf Islands. (Photo: Western University)

Reintroducing large predators to the islands could have theoretically brought things back into balance, but that’s an unpopular option that no one has seriously considered. Instead, Suraci and a team of other researchers decided to introduce something simpler.

Fear.

Over the course of two years, the researchers installed an array of speakers along the coasts of several Gulf Islands. They then pumped the sounds of domesticated dogs over the speakers to see if the noise of a possible predator would stop raccoons from their constant foraging.

It not only worked—it exceeded the researchers’ expectations. “We saw 66 percent reduction in raccoon foraging just from fear itself,” Suraci said.

The raccoons not only spent less total time stuffing their faces but also spent more time moving from each feeding site—essentially fleeing from the predators they suspected were nearby.

RELATED: On the Brink of a World Without Large Predators

The ecosystem noticed. By the end of the researchers’ experiment—documented this week in a study published in the journal Nature Communications—the raccoons’ prey had dramatically bounced back. Intertidal crab populations increased by 97 percent, fish increased by 81 percent, and the red rock crab population grew by 61 percent.

“It essentially reversed the impact of the raccoons,” Suraci said.

That meant that some other species declined. The suddenly more abundant red rock crabs subsequently ate more periwinkle snails, which declined by about half. That might have a benefit, though, as the paper calls periwinkle snails “significant grazers” and suggests that some vegetation might now have a chance to become more abundant, another sign that the raccoons were pushing the entire ecosystem out of balance.

Suraci doubts the fear-introduction technique could become a permanent solution—animals can learn if predators make sounds but never appear, he said—but it could be helpful in more limited situations. For example, he said, fear-inducing sounds could be useful for keeping small predators away from endangered birds while they are nesting.

He said the study adds to our understanding that “having carnivores on the landscape is good for the ecosystem.” Suraci added that he hopes the study will help support the idea of predator reintroduction and that people should be more willing to share their landscapes with large carnivores.

Just don’t tell the raccoons.