An experiment involving raccoons and speakers emitting the sound of barking dogs on tracts of beaches on British Columbia’s Gulf Islands shows that the fear of large carnivores has a positive impact on ecosystem health. The study led by University of Victoria PhD student Justin Suraci with support of the Raincoast Conservation Foundation is published on 23 February in Nature Communications.
Raccoons on the British Columbia’s Gulf Islands are devastating populations of crabs and fish in the intertidal zone, and nesting songbirds on land. Suraci and co-researchers Liana Zanette (Western University) and Larry Dill (Simon Fraser University) suspected this was due to raccoons having little to fear, because the formerly nocturnal raccoon populations now forage unabashedly day and night in the intertidal zones.
What happens when island raccoons live free of predators? A lot. And it’s not good.
Raccoons are cocker-spaniel-sized creatures native to the Americas. Normally, raccoons are mesopredators – animals in the middle of the food chain – part of an ecological niche they share with other medium-sized omnivores, such as skunks, badgers, and foxes. But on some of British Columbia’s Gulf Islands, raccoon populations have no natural predators and no fear of becoming another animal’s lunch. Follow ecologists Mike Clinchy and Justin Suraci in the field as they study the effects of raccoons foraging in the intertidal zone, barely watching for danger as they rip apart countless crabs and other prey species:
(Source: Hakai Magazine Vimeo channel)
To investigate whether fear of dogs – a top (or apex) predator since the elimination of wolves, bears and cougars from the Islands almost a century ago – could affect raccoon foraging behaviours along the shoreline, they played threatening dog sounds from speakers along extensive tracts of shoreline for one month.
See how the raccoons flee from the recorded barks:
(Source: New Scientists YouTube channel)
They found that raccoons reduced their foraging time by 66 per cent. In that period, researchers recorded a 61 percent increase in the abundance of red rock crab and an 81 per cent increase in intertidal fish – a prime target of raccoons.
“Humans have done an excellent job of wiping out large carnivores across the globe and we’re only starting to understand what the ecological consequences of that are,” says Suraci. “One of the major consequences is that when you take away the large carnivores, you get outbreaks of the species that they eat – herbivores like deer and smaller predators like raccoons. So, understanding the ways in which these large carnivores historically kept their prey in check was very important to restoring these ecosystems.”
Justin Suraci, lead author, Department of Biology, University of Victoria, British Columbia, Canada:
(Source: University of Victoria media release, 23.02.2016)