Synthesis of noise effects on wildlife populations.

Synopsis: This paper summarizes significant findings from literature related to the effect of noise on wildlife, emphasizing the effects of road traffic noise on birds. Many studies from the United States and the Netherlands indicate that road noise has a negative effect on bird populations, particularly during breeding season in a variety of species. In this paper, ‘effect distances’—distances at which bird density decreases—are reported at a range of two to three thousand meters from the road. Effect distances tend to increase with traffic density, being the greatest near large, multilane highways. In a study of woodland species, 26 of 43 (60%) were found to show a decrease in population densities with effect distances that also increased with the amount of traffic. Based on cumulative results, sound levels above 50 dB could be considered detrimental to many bird species. Findings that illuminate the relationship between reduced population density in some species and traffic density support the idea that noise has a significant effect on these species. However, the effect is not universal and needs to be considered in terms of the surrounding habitat as well as species in question.