Noisy nests not for the birds

U. COLORADO (US)—Birds favor quiet over clamor, according to a new study that presents the strongest evidence to date that noise pollution negatively affects bird populations. The findings may have implications for the fate of ecological communities situated near urban bustle.

The University of Colorado at Boulder study also is the first to indicate that at least a few bird species buck the trend and opt for noisy areas over quiet ones. The researchers suspect vocalization pitches, a reduction in nest predators, and less competition from other songbirds may be important factors.

“This is the first study to show that noise pollution causes changes in species interactions within bird communities,” says Clinton Francis, the study’s lead author and a doctoral candidate at UC-Boulder. “Since noise pollution can be a major cause of declining bird diversity in and around urban areas, better noise control using quieter road surfaces and sound-reducing walls and berms should be considered to help preserve such communities.”

The three-year study, conducted in a parcel of woodland south of Durango, Colo.,  was one of the first done in a controlled environment—the team worked with energy companies to shut down gas pad compressors for several hours each week, allowing researchers to identify individual nests and determine nesting success.

The researchers found that 32 different bird species nested in the quiet areas undisturbed by noise pollution, while only 21 species were nesting in the noisy study sites. The team also found only three bird species nested exclusively at the noisy sites, while 14 different bird species nested only in the quiet sites, says Francis.

Francis explains the two species that preferred noise—house finches and black-chinned hummingbirds—both produce vocalizations at higher acoustic frequencies than those generated by compressors, which may allow them to communicate above the “industrial rumble” and subsequently nest there. Common in congested urban areas, house finches also are known to sing at higher frequencies in response to urban noise, he says.

Higher nesting success at noisy sites by house finches, black-chinned hummingbirds, and of other species was also due to lower levels of predation by a major nemesis of the birds—the  western scrub jay—which was shown to prefer the quiet woodland sites.

Western scrub jays, which are known to prey on eggs and young of songbirds, play a key role in Southwest woodland ecology, says Francis. They were shown to be 32 percent more common in the quiet areas, perhaps in part because some of their vocalizations were in the same range as the compressor noise and inhibited communication.

The study indicated birds that were intolerant of noise and nested in quiet areas were subject to greater rate of nest predation than those in noisy areas. Woodland birds that prefer noisy areas may even use the clamor of civilization as cues for nesting, since such noise might signal a reduction in potential predators.

The researchers also found that a number of bird species found in the noisy sites—including gray flycatchers, gray vireos, black-throated gray warblers, and spotted towhees—tended to avoid areas of noise disturbance when selecting nesting sites.

“Understanding how birds respond to noise, especially birds with critical links to ecosystems, are crucial in maintaining biodiversity in growing areas of landscapes disturbed by urban clamor,” says Francis.

The study was funded by a number of organizations, including the Bureau of Land Management and the University of Colorado. Findings were published online July 23 in Current Biology.

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