Once upon a time, bears, mountain lions, and wolves ran the show in British Columbia's Gulf Islands. They're gone now. These days, raccoons are in charge, and they've taken a big bite out of local crab and fish populations. What to do? Play the sounds of dogs barking. Just hearing the sound of an aggressive predator will keep raccoons from going to town on marine life, according to a new study.
Whether they're really a threat to people, humans have gone to great lengths to "extirpate" large predators, a team of biologists led by University of Victoria graduate student Justin Suraci writes today in Nature Communications. That's messed with ecosystems in more ways than one. It has, of course, removed top-level predators, leading certain populations of animals like raccoons to boom. It's also done something more subtle: Without the stuff of Procyon lotor nightmares roaming around, raccoons have grown bolder—and eaten deep into crab and fish populations. Curbing raccoons' marine gluttony could be essential to restoring some measure of natural balance. The question is, could fear alone do the trick?
Crabs that lived mostly under water were 50 percent more common when raccoons were scared off by dog barks.
To find out, Suraci and his colleagues from the University of Virginia, Raincoast Conservation Foundation, the University of Western Ontario, and Simon Fraser University first recorded domestic dogs, harbor seals, and Stellar sea lions barking. While those sounds are all somewhat similar, only dogs are a threat to raccoons, and so only dogs' barks should scare raccoons. Next, the team made 11 "playlists" of dog barks and nine of seal barks, each comprising clips lasting between eight and 79 seconds. Then, the team set up speaker systems on the coasts of four of the Gulf Islands, a chain that lies in the Salish Sea between Vancouver Island and mainland British Columbia and Washington state. After that, they let one of the bark playlists run for 28 days, followed by a week's break, and then 28 days of the other bark playlist.
During the month of dog barks, raccoons spent much less time hanging around looking for food, and they were about half as likely to stick around after spending 10 seconds listening to dog barks, compared with seal barks. That had a major impact on marine life. After a month of dog barks, crab and fish populations in the intertidal zone—the area covered by water at high tide and exposed to air at low tide—were double what they were after a month of seal barks. Even crabs that lived mostly under water felt the effects: They were 50 percent more common when raccoons were scared off by dog barks.
"Our experimental results support the contention that, when it comes to conserving biodiversity and maintaining healthy ecosystems, fear has its uses," the biologists write.
But the real point, they argue, isn't that we should run around playing dog barks. Instead, we need to set aside our own fears and bring back mountain lions and bears, so they can do a job they were meant to do.
Quick Studies is an award-winning series that sheds light on new research and discoveries that change the way we look at the world.