As governments pledge to combat climate change, wind turbines are becoming a common feature of terrestrial and marine environments. Although wind power is a renewable energy source and a means of reducing carbon emissions, there is a need to ensure that the wind farms themselves do not damage the environment. There is particular concern over the impacts of wind farms on bird populations. In this thesis I have explored how to assess the cumulative impacts of wind farms on birds.
Cumulative impact assessment is a legislative requirement of environmental impact assessment but too frequently it has been tacked on to the end of assessments as an afterthought. Reasons for this are numerous but a recurring theme is the lack of clear definitions and guidance on how to perform cumulative assessments. Therefore I developed a conceptual framework to promote transparency. The core concept is that explicit definitions of impacts, actions and scales of assessment are required to reduce uncertainty in the process of assessment and improve communication between stakeholders. Only when it is clear what has been included within a cumulative assessment, is it possible to start to make comparisons between developments. I also recommend a more strategic approach to cumulative impact assessment.
If birds avoid wind farms then the structures act as barriers to movement and birds must fly further to reach their destination. If the additional distance has an associated energetic cost then this will impact an individual. With data collected using surveillance radar, I investigated the impact of the Nysted offshore wind farm on a population of common eider Somateria mollissima migrating from Finland to the Wadden Sea. The impacts of the wind farm appeared trivial and it required 100 equivalent wind farms before a significant impact was detected. Using the same radar data I also constructed a model to quantify the movement process of birds in response to wind turbines and therefore provide wind farm developers with a useful tool to predict the impacts of different wind farm designs.
The impacts of wind farms may be greater for birds that interact with the turbines on a daily basis than for migrating individuals. Using an energetic modelling approach I explored the impact for a suite of breeding seabirds commuting past a wind farm between their breeding and feeding areas. Impacts of flying increasing distances associated with increasing numbers of wind turbines were species-specific and costs were highest for species with high wing loadings and high daily frequency of foraging flights. However, costs of extra flight to avoid a wind farm appear much less than those imposed by low food abundance or adverse weather conditions.
Finally, a spatially-explicit individual-based model was developed to assess cumulative impacts of wind turbines through collision mortality and direct and indirect habitat loss, on a population of hen harriers Circus cyaneus on Orkney. Increasing numbers of wind turbines caused declines in the hen harrier population but the population response varied according to where turbines were located. Therefore, although wind turbines impact hen harriers, it may be possible to reduce the effects by considering hen harrier ecology during the planning procedure and/or implementing mitigating measures such as rough grassland restoration in strategic locations away from turbines.