Could roads be simplifying bird communities?
Written By Sophia Cooke
9th November, 2020
Great Britain has one of the densest road networks in the world with a total road length equivalent to almost ten times the Earth’s circumference. In the past half century, traffic levels on these roads have increased by over 160%, while, over the same period, many British bird species have seen steep and widespread declines. However, we have limited understanding as to the extent of a link between the two.
Roads can negatively impact wildlife, including birds, through noise, light and air pollution, as well as collisions. Noise is thought to be the biggest impact of roads on birds, disrupting their ability communicate and to detect predators and prey. However, roads can also benefit some species by providing varied habitat, food in the form of road-kill, and perches in the form of powerlines and fences.
Investigating a link between roads and bird populations
We assessed the spatial associations between roads and birds across the whole of Britain using count data from the UK Breeding Bird Survey. Of the 75 species analysed, the abundance of 77% varied significantly around roads, just over half negatively so. We found that species with smaller national populations, such as yellow wagtails and green woodpeckers, generally had lower abundance with increasing road exposure, whilst the opposite was true for more common species, such as blackbirds and wood pigeons. We also found smaller-bodied and migrant birds, such as chiffchaffs, to be mostly in lower abundance around roads.
With some bird species appearing to tolerate road disturbance better than others, it is therefore possible that roads may be leading to simplification of avian communities by creating conditions that benefit already common species at the expense of others. This phenomenon has been identified in both urban and agricultural environments, and in response to climate change, but this is the first evidence to suggest parallel impacts of roads.
Strikingly, the distance over which the negative associations between roads and bird populations could be detected averaged 700 m, an area which represents over 70% of Britain and over 40% of the total area of conservation protected sites.
Associations between roads and bird populations were found up to an average of 700 m from a road, meaning bird populations in over 70% of Great Britain and over 40% of the total area of conservation protected sites are potentially impacted by roads.
A need for mitigation
In a global, as well as a national context, the potential impacts of roads on bird populations and communities could therefore be substantial. Yet, to date, roads have largely been overlooked as a threat to biodiversity at governmental level, though further road building and traffic increases are expected in Britain and across the globe.
The best methods of mitigating road impacts are clearly to reduce the number of vehicles, by e.g. increasing available and affordable public transport, to reduce the number of roads and to plan their locations better, ideally avoiding biologically sensitive areas. Secondary to these efforts, remaining impacts should be minimised as much as possible. As noise is likely the most important mechanism by which roads can affect birds, measures to reduce its impact through e.g. noise barriers, different road surfaces, and lower speed limits in certain areas, are a useful starting point.
It is not only birds that are sensitive to roads but many other taxa too, including mammals, amphibians, fish and invertebrates. It is also becoming increasingly evident that humans are not exempt either, with various illnesses being linked to road noise and air pollution. Rather than impacts on people and various taxa being considered separately, a multi-species (including humans) approach to road mitigation could be more effective and efficient and this should be considered as imperative, both in Britain and further afield.
Source:
Cooke, S.C., Balmford, A., Donald, P.F., Newson, S.E. & Johnston, A. (2020). ‘Roads as a contributor to landscape-scale variation in bird communities’, Nature Communications, 11 (3125). https://www.nature.com/articles/s41467-020-16899-x
5-minute summary: https://youtu.be/l4MCXUR2IGQ
Editor:
Rodney van der Ree
Cite this summary:
Cooke, S. 2020. Could roads be simplifying bird communities? Edited by van der Ree, R. TransportEcology.info, Accessed at: https://transportecology.info/research/roads-simplifying-bird-communities [Date accessed].