Noise Keeps Animals From Recognizing the Scent of Danger

BS Thurner Hof via Wikimedia Commons // CC BY-SA 3.0
BS Thurner Hof via Wikimedia Commons // CC BY-SA 3.0 / BS Thurner Hof via Wikimedia Commons // CC BY-SA 3.0

Picture this: you’re driving somewhere you’ve never been before, blasting your favorite tunes. As you approach your destination and start checking house numbers, your hand reaches for the dial and turns the radio down. Without even realizing it, you’ve decided to redirect your attention from sounds to sights. Now imagine that your passenger has interfered. They’ve turned the radio all the way up and opened all the windows, filling the car with the roar of traffic and wind as you’re trying to focus. Harder now, isn’t it? And it isn’t just us; scientists say mongooses exposed to traffic noise overlook crucial clues from their other senses—clues that could mean the difference between life and death. Their findings were published today in the journal Current Biology.

We’ve known for a long time that pollution and urbanization are bad news for everyone. Much of our research has focused on the physical effects like smog, water contamination, and habitat destruction. We haven’t paid too much attention to the toxic effects of too much noise until recently, but what we’ve learned is troubling.

Studies have shown that exposure to anthropogenic, or human-made, noise causes intense stress for animals, can interfere with their communication, and may even keep them from migrating and having sex. All of these issues could mess with a species’ chances of survival in the long run.

The short-term effects have been less understood, says biologist Amy Morris-Drake of the University of Bristol. She and her colleagues decided to test the immediate consequences of noise on one species, the dwarf mongoose (Helogale parvula), whose South African habitat is increasingly bounded by cities and roads.

The dwarf mongoose has many predators, including jackals, hyenas, civets, servals, honey badgers, wildcats, bigger mongooses, and an assortment of reptiles. The key to survival, consequently, is constant olfactory vigilance: sniffing the air for the scent of predator poop.

The research team headed into mongoose territory with audio recordings of traffic noise and Ziploc baggies of poop from servals, wildcats, and giraffes. (Because giraffes present no threat to mongooses, their poop was used as a control group.) The researchers set out the poop and played their road sounds, watching the mongooses to see how they would respond.

The results were not encouraging. Exposure to traffic noises significantly decreased the mongooses’ vigilance. They spent less time investigating the predator poop; they were less likely to scan the area for potential threats; and they were less likely to retreat to the entrance of their burrow to prepare for an attack. If the scientist-provided poop, and therefore the threat, had been real, those mongooses would have found themselves in significant danger.

"Our study suggests that noise pollution can have a negative effect in terms of information use,” said co-author Andy Radford. “Given the demonstrated effects, considering the interactions among multiple sensory channels is critically important if we are to understand fully the consequences of human-induced environmental change."
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