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, said Francis.
Two bird species preferred the noisy sites, he said. Ninety-two percent of the black-chinned hummingbird nests and 94 percent of house finch nests in the two study areas were found at sites near noisy compressors. The two species accounted for 31 percent of the nests at the noisy sites, but less than 3 percent on the quiet sites, said Francis.
Francis said house finches and black-chinned hummingbirds 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, he said. Common in congested urban areas, house finches also are known to sing at higher frequencies in response to urban noise, said Francis.
Higher nesting success at noisy sites by house finches, black-chinned hummingbirds and of other species was 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, said 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.
Since scrub jays frequently carry, eat and cache pine nuts and disperse them throughout Southwest woodland ar
|Contact: Clinton Francis|
University of Colorado at Boulder