The sound that strikes fear into a raccoon's heart? Man's best friend
Tricking the animals into thinking they hear a predator can keep the masked bandits in line and help restore balance to an ecosystem, researchers find.
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If a tree barks in the forest, do raccoons get scared?
Apparently they do, according to a new Canadian study published last month in the journal Nature Communications.
University of Victoria PhD candidate Justin Suraci discovered the raccoon-ridding remedy after a soundtrack of animal calls ranging from bears and sea lions to man’s best friend was tested on B.C.’s Gulf Islands.
Prior to the experiment, raccoon life on the small islands in the Strait of Georgia was peaceful. The absence of natural predators such as bears and cougars, many of which were killed off by humans a century ago, means the critters can raid the tidal flats for food — more tasty crab and fish, less green bin scraps — all day long.
“It is officially raccoon paradise out here,” said Suraci, the study’s lead author. “They have huge numbers and are strikingly fearless in their behaviour.”
The fear of being eaten alive, he explained, can influence an animal’s lifestyle in several ways, from how it searches for food to how it reproduces.
Suraci started the experiment by attaching speakers and video cameras to trees along the shoreline. Each station was powered by the equivalent of a car battery and programmed to randomly play sounds of a black bear, cougar, harbour seal or sea lion.
“You need to be able to use fear creatively,” said Suraci, noting that each recording was adjusted to be played at the same volume for a month straight.
None of the predators’ calls was able to strike as much fear into the scavengers’ tiny hearts as a fifth recording — the domestic dog. Footage collected during the study shows raccoons hightailing it from the beach to the woods immediately after hearing a bark.
Suraci said the scaredy-cat response was likely influenced by prior run-ins with canine carnivores who visit the island with their owners. In other words, the bark had bite.
“A large number of these raccoons would have directly experienced being chased, barked at or harassed by a dog,” said Suraci. “So you need the actual predators to back up the sound with a credible threat.”
The implications of the study went far beyond the raccoons’ fright. Suraci noted the barking soundtrack caused the animals to spend 66 per cent less time foraging for seafood on the shorelines. After a month’s worth of barking had passed, heavily depleted raccoon food sources, such as the red rock crab, quickly repopulated.
Suraci believes an animal with nothing to fear is an ecological liability for the rest of the food chain.
One of his co-authors, Western University’s Liana Zanette, scared songbirds with hawk and owl calls during the nesting season. The songbirds raised 40 per cent fewer chicks as a result.
One of the best-known examples of predatory fear keeping nature in check originates in Yellowstone National Park.
Grey wolves were reintroduced to the U.S. park in the 1990s after a 70-year hiatus, and ended elks’ carefree grazing days. Coincidentally, the herbivore elks reproduced less, while the aspen and willow saplings they loved to munch on began to reappear. Whether or not this ecosystem facelift was caused by the wolves, though, is the subject of heated scientific debate.
By directly manipulating fear itself — in this case, using a speaker strapped to a tree — Suraci and his colleagues were finally able to prove that the mere perception of a predator can restore balance to an ecosystem.
“Instead of having their face buried in food, the raccoons were more nervous and looking behind their shoulder for predators,” he said.
Suraci added his study may hold potential for targeting pest raccoons as part of an urban wildlife management strategy. But the idea of installing canine-soundtrack speakers in Toronto may be a tough sell.
“First and foremost, we are still creating the perfect nirvana for raccoons in Toronto,” said Nathalie Karvonen, director of the Toronto Wildlife Centre. “People are still feeding raccoons, there are overflowing dumpsters and it’s a smorgasbord of an endless food supply.
“So doing this to terrorize raccoons is not very nice.”