Are the negative effects of roads on breeding birds caused by traffic noise?

Abstract

Summary1. The effects of roads on wildlife populations are widespread and well documented. Many studies have shown that bird abundance, occurrence and species richness are reduced near roads, with the largest reductions where traffic levels are high. Negative correlations have been reported between bird richness ⁄ abundance and traffic noise but the possible causes of road effects are inter-correlated. It is important to disentangle the different effects so that appropriate mitigation measures can be implemented. 2. We tested the hypothesis that traffic noise is a key negative effect by testing three predictions: (i) bird richness ⁄ abundance should reach a maximum at the same distance from roads that traffic noise reaches a minimum; (ii) the effect of traffic noise on bird richness ⁄ abundance should be stronger than the effect of distance from the road on bird richness ⁄ abundance; and (iii) sites with more traffic noise at a given distance from the road should show lower bird richness ⁄ abundance than sites with less traffic noise at the same distance. 3. We collected breeding bird occurrence and traffic noise data along twenty 600-m transects perpendicular to roads at 10 high-traffic road sites. 4. Traffic noise decreased and bird species richness increased with increasing distance from the roads. However, none of the predictions derived from the traffic noise hypothesis was supported. 5. Synthesis and applications. Our results suggest that traffic noise is not the main cause of the negative relationship between bird species richness ⁄ abundance and proximity to roads. Instead, traffic mortality may be the main mechanism causing this relationship. We suggest that mitigation of road impacts on birds should focus mainly on reducing mortality rather than reducing traffic noise. In particular, engineering road surfaces, tyres and vehicle engines to reduce noise would not mitigate road effects; instead, structures to keep birds away from roads or force them to fly above the traffic would be more effective.

Major Roads Have a Negative Impact on the Tawny OwlStrix alucoand the Little OwlAthene noctuaPopulations

“…occupy habitat patches sufficiently far from major roads, which is consistent with all the potential negative road effects previously described. The adverse effects on Tawny Owl density may be observed up to distances of 2 km from major roads, which seems further than the area affect by vehicle-noise, which may suggest that noise could not be the main cause of this negative relationship (Summers et al 2011). The distance-effect we observed for Tawny Owls is somewhat similar to those found for several other bird species, which are often larger than 1 km (van der Zande et al 1980, Reijnen et al 1995, Benítez-López et al 2010.…”

“…Since this measure has significant costs, its implementation must always be supported by scientific evidence, and it should occur in priority areas holding important owl assemblages. However, our results do not enable us to draw any strong conclusion about the effect of traffic noise on owls, and recently this negative effect has not been supported in diurnal birds (Summers et al 2011). Noise barriers can have an additional advantage of reducing bird mortality by collision with vehicles by forcing birds to fly over passing vehicles (Pons 2000), but this measure should always consider possible barrier effects on other animals, and must be applied along with under-or over-passes for wildlife.…”

“…However, traffic noise is considered to have the greatest negative indirect effect on birds (Reijnen et al 1995, Kociolek et al 2011, but see Summers et al 2011), reducing population density in several bird species (Patricelli & Blickley 2006, Reijnen & Foppen 2006, Barber et al 2010, Goodwin & Shriver 2011. Traffic noise increases with vehicle speed and type, and also traffic intensity, being greater in major roads and highways (Reijnen et al 1995).…”

Effects of Road Density and Pattern on the Conservation of Species and Biodiversity

“…For species that use vocalizations to undertaken crucial life history stages (such as song birds and amphibians; [61,62]) or reply on sound to avoid predators, navigate and forage (such as bats and amphibians; [63,64]), any noise that can mask sound can have a detrimental impact. For example, three studies demonstrated that bird diversity decreased as a result of road-related noise [65][66][67]. Another study showed that the foraging efficiency of Daubenton's bats (Myotis daubentonii) decreased when vehicle noise masked their echolocation calls, which in turn lead to the avoidance of roadside habitat [64].…”

Traffic Influence on Roadside Bird Abundance and Behaviour

“…For instance, the Netherlands has 1.5 km and the U.S. 1.2 km of roads per km 2 land area (Forman & Alexander 1998). Many studies demonstrate the negative effects roads have on wildlife are due to habitat loss, population fragmentation, pollution, poisoning, noise, and collisions with cars (Erritzøe et al 2003, Reijnen & Foppen 2006, Fahrig & Rytwinski 2009, Francis et al 2009, Goodwin & Shriver 2011, Summers et al 2011). This also extends beyond the road lanes and verges, and bird densities are in some cases reduced as far away as 1-3.5 km from the road , Reijnen et al 1996, Forman et al 2002, Benitez-Lopez et al 2010.…”