Study: Humans are too noisy for nature |

Study: Humans are too noisy for nature

Julie Sutor
Summit County correspondent
Aspen, CO Colorado
Colorado Division of WildlifeBiologists trying to study human-lynx interactions on Vail Pass are having trouble finding the rare cats.

Loss of habitat, chemical pollution and physical changes to habitat get the lion’s share of attention when it comes to human impacts on wildlife, including extinction. But a growing body of evidence suggests that human-generated noise is also interfering with animals’ abilities to mate, avoid predators, locate prey, forage and perform other essential behaviors.

In a study published this month in the journal Trends in Ecology and Evolution, researchers from Fort Collins said that anthropogenic noise affects wildlife in habitats all over the world, even in remote wilderness areas. And that noise has increased substantially in recent decades, both in reach and intensity.

Researchers Jesse Barber, Ph.D., and Kevin Crooks, Ph.D., of Colorado State University and Kurt Fristrup of the National Park Service’s Natural Sounds Program reviewed nearly 100 studies documenting effects of human noise, such as roads, airplanes, recreation and energy extraction.

“Chronic noise exposure is widespread,” the authors wrote. “Taken collectively, the preponderance of evidence argues for immediate action to manage noise in protected natural areas.”

One of the most important phenomena at play is “masking” – chronic noise’s interference with an animal’s perception of sound.

Masking can come into play, for example, when a noisy highway prevents a female bird from perceiving the full range of male mating calls, thereby interfering with her selection of an optimal mate. Masking might also interfere with a pika’s ability to hear a warning sign from another pika about an approaching predator. Or an elk might not hear the footfall of a wolf in time to avoid becoming the predator’s next meal.

According to Fristrup, masking could be of particular concern to one Summit County native whose populations are dwindling: the greater sage grouse.

“The male sage grouse, in its mating displays, produces high-frequency popping sounds and swishing sounds,” Fristrup said in an interview with the Summit Daily. “It also uses a low-pitch hooting sound, which carries the farthest from the display area as a long-distance advertisement. The danger is, it doesn’t take a lot of noise to substantially reduce the range at which females or other males could hear that low-frequency hoot. So the attraction radius of the display ground could contract substantially with the inability to hear a hoot.”

The authors note that some species can reduce the effects of masking by shifting their vocalizations. This is especially true when members of a species are communicating with each other. However, when the sounds a species depends on emanate from another species, there is less room for compensation.

For example, the boreal owl, also native to Colorado, hunts its prey by listening to it scurry under the snow. Upon hearing a rodent, the owl plunges into the snow to blindly stab for it. The rodents that make up the owl’s diet leave no visible clues to their whereabouts, and the rodent has no incentive to compensate for the masking effect of anthropogenic noise.

“The cost of chronic noise is all the more serious for sounds that aren’t intentionally produced,” Fristrup said.

Animals such as lynx, foxes and coyotes will suffer less from masking, since they will likely compensate somewhat with other senses, such as sight. However, carnivores like lynx, who sit at the top of the food chain, can be particularly sensitive to habitat degradation of any type – including auditory – since each individual requires a huge hunting territory.

“If one part of the range of a top-level predator is compromised, it may not take much to squeeze it out,” Fristrup said.

Contrary to what one might expect, noise is not always more disruptive when it’s louder. Snowmobiles or cars, for example, might be less disruptive to elk or deer than a hiker or cross county skier would be.

“There’s pretty good evidence that so-called quiet use can disturb wildlife. If it’s a noisy source, the animal perceives it a long way off and can track its progress. There are no surprises, and it can go on feeding or doing whatever else. A quiet sound, like a snowshoer’s footstep, is only perceptible when it is very close, potentially startling the animal,” Fristrup said.

Fristrup noted that the quiet-versus-noisy effects can vary widely among species, depending on how each one uses sound for survival. Owls, for example, prefer very quiet environments.

Problems wildlife experience with noise are widespread throughout the U.S., including Colorado. The study’s authors note that the extent of human transportation networks has increased far more rapidly than has human population. As of 2003, 83 percent of land area in the continental U.S. was within 1 kilometer of a road.

“Between 1970 and 2007, the U.S. population increased by approximately one-third. Traffic on U.S. roads nearly tripled to almost 5 trillion vehicle kilometers per year. Several measures of aircraft traffic grew by a factor of three or more between 1981 and 2007,” the authors wrote.

Anthropogenic noise can even negatively impact humans, particularly in places like Summit County, where wildlife sightings are an important part of the draw.

“One of the best ways to see animals is to hear a sudden, accidental sound. Just as chronic noise degrades opportunities for prey, we should also be concerned about the visitor who misses out on the opportunity of a lifetime because some subtle signal is missed,” Fristrup said.

To appreciate the vulnerability wildlife experience because of chronic noise, Fristrup suggests a person imagine wearing noise-canceling headphones on a hike.

“It’s akin to the effect of smog or fog on vision. You can still see, but not as well. The same things happen with noise pollution. The chance of hearing rare things is reduced, or a sound might be fuzzy enough that you don’t recognize it for what it is,” he said.

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