In order to find out whether the fear of large predators is alone enough to change the behavior of their prey, scientists began scaring the crap out of raccoons. To wage this campaign of psychological terror, the researchers played the sounds of large carnivores at the bold, trash-toppling raccoons, for a month at a time.
Until now, says the new study published in Nature, nobody has tested the theory that the threat of a predator has an effect on the local population, separate from the actual effect of the predator killing and eating. This is important, because humans have eliminated large predators from most environments, which leaves creatures like raccoons to roam free, without fear of anything other than the odd hurled shoe or the occasional crazy old man with a shotgun.
The problem with testing the theory has been the "challenge of experimentally manipulating fear in free-living wildlife," says the paper, led by Justin Suraci out of the University of Victoria, British Columbia. Then they hit on the idea of barking dogs.
The experiment, conducted on Canada's Penelakut Island, used recordings of domestic dogs, along with recordings of the local harbor seals and sea lions, whose calls are similar to those of the dogs, making them a good control. Recordings ran between eight and 79 seconds.
The result, as you can see in the video, is that the dog sounds scared the bejesus out of the raccoons. It also significantly changed their behavior. With no predators to worry about, the raccoons would graze like the typical American buffet-goer, eating a bit of everything, and tossing aside what they didn’t want. "Island raccoons are living it up," says Ars Technica’s Annalee Newitz. "The nocturnal creatures are even coming out during the day to amble around on shore and eat. They sometimes eat just part of a crab and then leave the rest of the body floating in the water. As a result, crab and other raccoon-prey species are being decimated."
The dog recordings had an immediate and significant effect. By measuring the mortality rates of the raccoons’ prey, Suraci’s team found that the raccoons became more furtive, taking only what they needed instead of gorging on and wasting the local wildlife. The raccoons "spent 66% less time foraging over the course of the month," says the report, and following the month-long playbacks, "there were 97% more intertidal crabs, 81% more intertidal fish, 59% more polychaete worms, and 61% more sub-tidal red rock crabs."
In short, putting the frighteners on the raccoons all but cured their catastrophic impact on the local ecosystem.
But are recordings of large predators practical as a way to combat the rise of smaller predators? Suraci’s team recommends reintroducing large predators instead. After all, a loudspeaker sits in a single position, whereas predators will follow their prey, wherever it tries to hide. "By inspiring fear, the very existence of large carnivores on the landscape, in and of itself, can provide a critical ecosystem service human actions cannot fully replace, making it essential to maintain or restore large carnivores for conservation purposes," says the paper.
Don’t like the idea of sharing your space with wild dogs and tigers? Suck it up, says Suraci, and learn to love them. Living together, he says, "requires attenuating our own fear of them, which can be accomplished by promoting tolerance and coexistence with large carnivores."