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A phantom road experiment reveals traffic noise is an invisible source of habitat degradation
Edited by Gretchen C. Daily, Stanford University, Stanford, CA, and approved August 4, 2015 (received for review March 8, 2015)

Significance
Using landscape-scale traffic noise playbacks to create a “phantom road,” we find that noise, apart from other factors present near roads, degrades the value of habitat for migrating songbirds. We found that nearly one third of the bird community avoided the phantom road. For some bird species that remained despite noise exposure, body condition and stopover efficiency (ability to gain body condition over time) decreased compared with control conditions. These findings have broad implications for the conservation of migratory birds and perhaps for other wildlife, because factors driving foraging behavior are similar across animals. For wildlife that remains in loud areas, noise pollution represents an invisible source of habitat degradation.
Abstract
Decades of research demonstrate that roads impact wildlife and suggest traffic noise as a primary cause of population declines near roads. We created a “phantom road” using an array of speakers to apply traffic noise to a roadless landscape, directly testing the effect of noise alone on an entire songbird community during autumn migration. Thirty-one percent of the bird community avoided the phantom road. For individuals that stayed despite the noise, overall body condition decreased by a full SD and some species showed a change in ability to gain body condition when exposed to traffic noise during migratory stopover. We conducted complementary laboratory experiments that implicate foraging-vigilance behavior as one mechanism driving this pattern. Our results suggest that noise degrades habitat that is otherwise suitable, and that the presence of a species does not indicate the absence of an impact.
- traffic noise pollution
- songbird migration
- habitat degradation
- foraging-vigilance trade-off
- perceived predation risk
Footnotes
- ↵1To whom correspondence may be addressed. Email: heidiware{at}boisestate.edu or jessebarber{at}boisestate.edu.
Author contributions: H.E.W., C.J.W.M., J.D.C., and J.R.B. designed research; H.E.W., C.J.W.M., J.D.C., and J.R.B. performed research; H.E.W. and C.J.W.M. analyzed data; H.E.W., C.J.W.M., J.D.C., and J.R.B. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
See Commentary on page 11995.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1504710112/-/DCSupplemental.
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