Sound Science

How songbirds make themselves heard above city noise

Ovenbirds have better breeding success away from noisy natural gas compressor stations.

Garth McElroy www.featheredfotos.com

The noisiest species on the planet is also the most widespread. Sirens, engines, electrical transformers, fireworks, and myriad other noises are produced by Homo sapiens. From sonar and oil-exploration explosions at the bottom of the sea to supersonic jets and space shuttles in the upper atmosphere, human-generated noise pollution is inescapable.

Birds depend on sound to attract mates, defend territories, warn about predators, and maintain contact with family and flock members. How can they communicate with so much noise in the background?

Ovenbirds nesting in two sets of territories of equal quality, except that one set was located near loud natural gas compressor stations and the other near fairly noiseless oil well pads, were compared in a study published in the 2007 Journal of Applied Ecology. Few older, experienced birds attempted to breed in the noisy areas, and pairing success in those areas was significantly lower regardless of the age of the birds.

Studies in Europe and America indicate that in urban areas, some birds change the volume, pitch, or timing of their songs, possibly giving them advantages over species that can’t modify their songs as readily.

Vehicle noises are loud, of low frequency, and more prevalent by day than night. In a 2003 study along a German highway, birds singing in low frequency ranges were less abundant near the road than those singing higher pitches, which carry better over highway noise. One European bird that adapts well to urban conditions, the Great Tit, sings at a higher pitch in cities than elsewhere, and recent studies indicate that Song Sparrows in Oregon do this as well.

People raise their voices in noisy situations (the “Lombard effect”). Laboratory studies of Blue-throated Hummingbirds, Zebra Finches, and Budgerigars show that birds do this, too. It’s tricky to measure loudness in the field, but one careful field study of nightingales found higher song amplitudes when background noise was louder. And individual nightingales sang more quietly on weekends, when noise was lower, than the same birds did on weekdays.

Pure tones are heard more clearly than buzzes and trills against noise. Some frogs and birds near waterfalls and noisy streams call with more pure tones than their relatives in quieter habitats. Will birds in urban settings change songs to simpler, purer tones over time? More and more birds seem to be singing at night in cities. This may be a function of reduced traffic at night or artificial lighting. For these issues, more study is needed.

Those of us who make sound recordings of nature try to find places without unnatural noises. Perhaps to help both birds and humans, we should redirect our focus to reducing all this noise in the first place.

—Laura Erickson

For permission to reprint all or part of this article, please contact Laura Erickson, editor, Cornell Lab of Ornithology, 159 Sapsucker Woods Rd., Ithaca, NY, 14850. Phone: (607) 254-1114. email: lle24@cornell.edu