Bird and bat species' global vulnerability to collision mortality with wind farms revealed through a trait-based assessment.

Wind Farm - Dawn Balmer

Author(s): Thaxter, C.B., Buchanan, G.M., Carr, J., Butchart, S.H.M., Newbold, T., Green, R.E., Tobias, J.A., Foden, W.B., O'Brien, S. & Pearce-Higgins, J.W.

Published: September 2017  

Journal: Proc. R. Soc. B. Volume: 284

Digital Identifier No. (DOI): 10.1098/rspb.2017.0829

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In a changing world, the development of green energy is more important than ever. One of the most well-developed and cheaply available options is wind power, but there is evidence that wind farms can also have a negative impact on biodiversity. This 2017 study, funded by the Cambridge Conservation Initiative and led by BTO, is the first to look at the global impact of wind farms on bird and bat populations.

Although the most obvious threat from wind turbines is that of collisions, as birds fly into the turbine, the threats from wind farms are not solely collision-based. They also have the potential to displace species from their nesting or feeding areas, restrict movements, or destroy key habitats used by different species. The study reviewed 234 papers which look at both bat and bird collision rates with wind farms. These were then examined in relation to several of the factors that may play a role in collisions, including the physiological and behavioural traits of individual species, and the height and energy output of turbines.

The results show that birds using ‘artificial habitats’ (e.g. farmland or urban areas) run a higher risk of colliding with wind turbines than birds living elsewhere, although this could be due to the fact that many wind farms are located within such habitats. Perhaps unsurprisingly, migratory birds faced a greater risk than sedentary ones; similarly, species of bat which dispersed further, on average, had a higher risk of collision than those that didn’t. Out of the 362 bird species examined, 55 were considered as being ‘threatened’ by wind farms. Thirty-one of these were birds of prey, species that are generally slow to reproduce and which are more sensitive to the impact of losing breeding adults to wind turbines. Collision rates in general were predicted to be higher for bats than for birds, emphasising their vulnerability to wind farms.

Individually, larger turbines were associated with a higher collision rate than small turbines, but wind farms comprising a large number of smaller turbines resulted in the highest rates of collision. In practical terms this suggests that using a few large turbines may lower collision rates for birds, although it is worth noting that turbines with a capacity of more than 1.25 MW were linked to high collision rates for bats.

Given the growing demands for green energy, it is essential that we consider the impacts of wind farms on populations of both bats and birds, especially migrants and wide-ranging species. Taking into account knowledge of the birds and bats using an area when considering the placement of wind farms and individual turbines (e.g. by avoiding migratory flyways) could greatly reduce the risk of collisions. The work also underlines a need for more research to be carried out in emerging economies and in relation to offshore wind farms, both of which are areas where valuable information is currently lacking. This will surely help to find the delicate balance between a greener future and healthy biodiversity.  


Mitigation of anthropogenic climate change involves deployments of renewable energy worldwide, including wind farms, which can pose a significant collision risk to volant animals. Most studies into the collision risk of species with wind turbines, however, have taken place in industrialized countries. Potential effects for many locations and species therefore remain unclear. To redress this gap, we conducted a systematic literature review of recorded collisions of birds and bats with wind turbines within developed countries. We related collision rate to species-level traits and turbine characteristics to quantify the potential vulnerability of 9538 bird and 888 bat species globally. Avian collision rate was affected by migratory strategy, dispersal distance and habitat associations and bat collision rates were influenced by dispersal distance. For birds and bats, larger turbine capacity (megawatts) increased collision rates, however, deploying a smaller number of larger turbines with greater energy output, reduced total collision risk per unit energy output, although bat mortality increased again with the largest turbines. Areas with high concentrations of vulnerable species were also identified, including migration corridors. Our results can therefore guide wind farm design and location to reduce the risk of large-scale animal mortality. This is the first quantitative global assessment of the relative collision vulnerability of species groups with wind turbines, providing valuable guidance for minimizing potentially serious negative impacts on biodiversity. 


This study was a collaboration between BTO, RSPB, IUCN, BirdLife International, Conservation Science Group Cambridge, Imperial College London, University of Stellenbosch, and JNCC.

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