One group of scientists has figured out how to outfox the raccoons, ArsTechnica reports. On the Gulf Islands off the coast of British Columbia, Canada, raccoons have invaded and acted like party-crashers, eating any critters they can put in their mouths and devastating the ecosystem.
There were once bears, mountain lions, and wolves on these islands, and they kept raccoon populations in check. But as usual, humans killed the large predators, viewing them as dangerous. Now the only natural raccoon predators left on the islands are domestic dogs.
As a result, the critters were out day and night, eating songbirds, crabs, and fish, and lots of other creatures, TakePart reports. And all of this is having a huge impact on the entire ecosystem, said Justin Suraci, an ecologist with the Raincoast Conservation Foundation. Populations of many of the islands’ native species have plummeted by up to 90 percent as a result.
Suraci and a team of researchers considered the idea of reintroducing large predators; theoretically that could have brought the situation back into a natural balance, but it was an unpopular idea that no one had really considered.
But what if they could bring something simpler into the equation?
Something like good, old-fashioned fear.
Over a period of two years, Suraci and his colleagues set up an array of speakers along the coasts of several islands. Next, they played the sounds of domesticated dogs doing what they do best — barking — over the speakers to see if that would put a halt to the raccoons continual foraging.
It worked like a charm.
The raccoons spent considerably less time eating and spent more time moving away from each feeding site; in essence fleeing from the predators they thought were close by.
Suraci’s colleague, Liana Zanette, from the University of Western Ontario, realized this setting gave her the perfect chance to study how fear shapes an ecosystem, The Atlantic reports.
Obviously prey animals are aware that predators can kill, but that’s not the only way carnivores can affect their prey. Their presence is manifested through tracks, smells, sounds and glimpses, and this produces vigilance, apprehension, and stress in prey species. These animals soon learn there are safe areas where they can easily see predators, and dangerous areas where hiding places are common and escape trickier. That results in a landscape of fear, a virtual topography that exists within the minds of prey animals, replete with safe valleys and dangerous mountains.
Grey wolves were killed off decades ago in Yellowstone National Park, and when they were reintroduced in the 1990s, ecologists developed this concept. They were able to demonstrate that this was because the park’s elk now spent much of their time keeping an eye out for the wolves and this meant they ate less and sired fewer young, The Atlantic reports. The elk died in numbers far larger than the wolves were killing, and the effect was felt throughout the park’s ecosystems. Trees that the elk fed on now grew taller, providing more wood for beavers and more nesting areas for birds. Introducing the wolves managed to change the entire park.
Some studies disputed this, but the concept regarding the landscape of fear caught fire and moved into the world of experiments. Zanette demonstrated in 2011 that if song sparrows in the Gulf Islands heard the calls of hawks, owls, or other predators over speakers, they raised 40 percent fewer chicks. And that’s even if their nests were protected by nets and fences.
One year later, another researcher, Dror Hawlena, showed that spiders whose mouthparts were glued still frightened grasshoppers enough to change their metabolic rates, and the chemical composition of their bodies. This even changed the amount of nutrients they return to the soil when they die.
So Zanette had at least some evidence that fear could affect animal populations and landscapes, but she wanted evidence that large carnivores could also bring about the same effects. Which is where the raccoons came in.
Wanting to test the hypothesis, the researchers scared the heck out of raccoons for the next several months, ArsTechnica reports. Setting up speakers along two sections of Gulf Island coastline, the sounds of dogs barking were broadcast. The researchers set up cameras to measure the effect this would have on raccoons. The scientists also took samples so they could measure the population sizes of crabs and other raccoon food items.
They also used controls by taking samples in coastal areas where they broadcast sounds from non-predators, and in areas where they had not done any broadcasting.
It wasn’t long before they found that raccoons who heard the frightening dog barks spent 66 percent less time foraging during the month, and many quit coming out onto the coastline completely. No longer did they boldly prowl the beach devastating the local creatures. The raccoons were now warier and only took what they needed. That meant crab, fish, and worm populations bounced back rapidly. By the end of the month, the researchers wrote “there were 97 percent more inter-tidal crabs, 81 percent more inter-tidal fish, 59 percent more polychaete worms and 61 percent more sub-tidal red rock crabs.” So the ecosystem was bouncing back.
What the researchers had done, essentially, was to create an audio equivalent of a scarecrow. Just like a scarecrow, the sounds of the barking dogs created a sense of danger.
Suraci doesn’t think this technique will be a permanent solution; after all animals can learn if predators make sounds but don’t show up, he told Take Part. It could be useful in limited situations. Fear-inducing sounds could be used for keeping small predators away from endangered birds as they nest.
The study also reinforces that carnivores are good for an ecosystem, he noted. He’s hoping the study will lend support to the idea of reintroducing predators and said that people should be willing to share their landscapes with large predators.
Something the rest of the world should also learn.
