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February 2009 cover image of Davis Mountains State Park

Scout: Noise in Nature

Human-produced sounds can interfere with animals’ normal mating, feeding and hunting behavior.

By Melissa Gaskill

Bio-acoustician Bernie Krause has been recording sound in natural places around the world for 40 years. In nearly half of those locations, he says, human-generated noise has infiltrated the pristine acoustics of nature.

According to the National Park Service, 72 percent of visitors consider the opportunity to experience natural peace and the sounds of nature as one of the most important reasons to preserve our parks. But while unnatural noise may mar our enjoyment of the outdoors, it poses even bigger problems for wildlife.

“Noise interferes with all of the syntax a mammal, reptile, amphibian, bird or insect would articulate. Human noise crosses all the communication lines and covers all the frequencies,” Krause says. In 2001, a study measured stress enzymes in the feces of elk and wolves in Yellowstone National Park. “Whenever there were snowmobiles around,” Krause says, “elk and wolves showed incredible amounts of stress.”

Noise can mean life or death for some animals. Frogs, for example, sing in chorus to prevent predators from singling out any one individual. Airplane noise disrupts this synchronicity, allowing predators to easily pick off a frog or two. “Frogs are diminishing everywhere,” including in Texas, Krause says, “and one reason is human noise.”

Much animal vocalization is done either to defend territory or attract mates, and human noise can interfere with both. Studies show that in urban areas where traffic noise occupies low frequencies in the sound spectrum, birds are singing in increasingly higher frequencies, says Elizabeth Derryberry, a post-doctoral researcher at Louisiana State University’s Museum of Natural Science. Research also suggests that different birds use different acoustic space; singing in slightly different frequencies keeps them from drowning each other out. But city birds are essentially forced to compete for a smaller piece of the acoustic pie. In addition, birds in noisy environments are forced to sing louder, reports the National Park Service, which means that attracting a mate or warning of predators uses more of their precious energy. Urban birds also are likely to spend more time being disturbed by noises and, therefore, less time feeding, says Richard Heilbrun, Texas Parks and Wildlife urban wildlife biologist in San Antonio, making it more difficult for them to replace that energy.

In some settings, noise flushes nesting birds off incubating eggs. Military aircraft had affected nesting success of peregrines, says Raymond Skiles, acting chief of resource management at Big Bend National Park, until resource protection areas were designated on aeronautical charts. Boats can flush nesting shorebirds, leaving eggs and chicks vulnerable to predators. The National Parks Con-servation Association is working on a national boater education program in hopes of reducing this impact.

Because most cat species rely on hearing to hunt, Heilbrun adds, their hunting success decreases as noise increases. “Mountain lions and ocelots will specifically avoid roads, and noise is one of the factors,” he says. Certain wildlife simply won’t use noisy areas, says former park ranger Bryan Faehner, legislative representative for NPCA, so noise effectively limits the populations of these species.

It is worth noting that noise affects human health as well. Says Krause, “The physical effect of noise on us is incredible amounts of stress.” Fortunately, this is one problem easily solved. All we have to do is pipe down.

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