An experimental investigation into the effects of traffic noise on birds: The Phantom Road project
Many authors have suggested that the negative effects of roads on animals are largely owing to traffic noise. Although suggestive, most past studies of the effects of traffic noise on wildlife were conducted in the presence of the other confounding effects of roads, such as visual disturbance, collisions and chemical pollution among others. I will discuss experimental work where we applied traffic noise to a roadless area at a landscape scale—thus avoiding these confounds. We replicated the sound of a roadway at intervals—alternating 4 days of noise on with 4 days off—during the fall migratory period for songbirds using a 0.5 km array of speakers within an established stopover site in Idaho, USA. We conducted daily bird surveys and mistnetting along our ‘Phantom Road’ and in a nearby control site.
We document over a one-quarter decline in bird abundance and almost complete avoidance by some species between noise-on and noise-off periods along the phantom road and no such effects at control sites—suggesting that traffic noise is a major driver of effects of roads on populations of animals. Focusing on individuals that stayed despite the noise, we also demonstrate that songbirds show a near halving of ability to gain body condition when exposed to traffic noise during migratory stopover. This marked degradation in stopover efficiency may help explain declines in migratory songbirds worldwide. We conducted complementary laboratory experiments that implicate foraging-vigilance behavior as one mechanism driving this pattern. Taken together, our results show that noise pollution degrades the value of habitat that is otherwise suitable, and that a species’ presence does not indicate the absence of impact.