Roads have a multitude of effects on wildlife and biodiversity, particularly birds. While birds are able to fly over roads without much difficulty, research has shown a fall in bird population densities in areas with high road traffic (Koehler, 2016). Some direct causes of this observation are environmental degradation resulting in the loss of suitable habitats, deaths from vehicle collision, and air pollution and poisoning from vehicles and road maintenance activities (Kociolek et al., 2011; Xie et al., 2021).
While these well-known, direct effects of roads on bird population and species richness have been extensively reviewed, fewer strands of literature have touched upon the indirect effects of roads, such as traffic noise. Surprisingly, it is these indirect causes that might actually have more significant impacts on bird populations than direct causes (Kociolek et al., 2011).
As such, even in the absence of direct threats posed to birds by roads and vehicular traffic, it is not uncommon for many bird species to exhibit clear avoidance behaviours to roads (Bollinger and Gavin, 2004; Kociolek et al., 2011).
Traffic noise is observed to have the most rampant and consequential indirect impacts on birds, with multiple studies showing the detrimental effects of road traffic noise on bird communities, breeding cycles, foraging, and communication (Kociolek et al., 2011).
In 2013, a novel research study, which involved the setting up of a “phantom road” in south-western Idaho, United States, was conducted to isolate the effects of traffic noise on bird distributions without the presence of other confounding factors associated with roads (McClure et al., 2013). Using the method of noise playback, the researchers added a 0.5 kilometres series of speakers playing road traffic noises at a popular bird migratory stopover site (McClure et al., 2013).
Almost all of the 59 bird species detected were disrupted by road traffic noise, with a fall in bird abundance by more than 25% along the “phantom road” and two species (Cedar Waxwings and Yellow Warblers) being essentially absent from areas near the phantom road under noise-on conditions (McClure et al., 2013). Migratory bird species were also observed to be more greatly affected by traffic noise than its resident counterparts, actively shifting their flight path towards more secluded and quieter areas nearby due to their innate mobility (Koehler, 2016).
This highlights that traffic noise is a chief driver of the detrimental impacts of roads on surrounding biodiversity (McClure et al., 2013). Perhaps moving forward, the examining of different sources of ambient road noises and their frequencies can help identify which bird species are most vulnerable to the threats associated with roads and traffic. Management actions should also consider an increase in vegetation coverage along roads to absorb sound (Kociolek et al., 2011).
References:
Bollinger, E. K., & Gavin, T. A. (2004). Responses of nesting Bobolinks (Dolichonyx oryzivorus) to habitat edges. The Auk, 121(3), 767-776.
Kociolek, A. V., Clevenger, A. P., St. Clair, C. C., & Proppe, D. S. (2011). Effects of road networks on bird populations. Conservation Biology, 25(2), 241-249.
Koehler, P. (2016). Why didn’t the bird cross the road? Traffic noise & its impact on birds – FeederWatch. Retrieved 9 March 2022, from https://feederwatch.org/blog/why-didnt-the-bird-cross-the-road-traffic-noise-its-impact-on-birds/#:~:text=The%20distribution%20of%20migratory%20birds,feeders%20in%20high%20traffic%20areas.
McClure, C. J., Ware, H. E., Carlisle, J., Kaltenecker, G., & Barber, J. R. (2013). An experimental investigation into the effects of traffic noise on distributions of birds: avoiding the phantom road. Proceedings of the Royal Society B: Biological Sciences, 280(1773), 20132290.
Xie, S., Wang, X., Yang, T., Huang, B., Wang, W., Lu, Z., Han, B., & Ouyang, Z. (2021). Effect of highways on breeding birds: Example of Hulunbeier, China. Global Ecology and Conservation, 27, e01554.