Scotland is committed to meeting 100% of its electricity demands from renewable sources by 2020. Marine renewables are a significant contributor to these targets, but the industry must comply with strict legislation (EU Birds Directive [2009/147/EC]) that protects internationally important seabird populations. This is a critical challenge because marine renewable developments have the potential to impact on seabird populations. The two effects that have received the most attention are collisions with turbine blades and displacement from developments (Drewitt & Langston 2006; Larsen & Guillemette 2007; Masden et al. 2010; Grecian et al. 2010, Langton et al. 2011, Scottish Government 2011). Other factors that may be important include barrier effects to the movement of migrating or commuting birds, disturbance during construction and operation, contamination, noise and indirect effects via impact of developments on seabird prey.
This project will focus on the means by which marine developments may affect seabirds from displacement and barrier effects. If the development is located in a foraging area then birds can be displaced, a process that may equate to habitat loss. If the development is on a route used by birds for daily or seasonal commuting then this may create a barrier to movement, potentially forcing affected individuals to travel further to meet their requirements.
This project first undertook a literature review of displacement and barrier effects (see Appendix A). This review demonstrated that there is considerable uncertainty about the potential impacts on seabird populations from these effects. To assess the state of knowledge, displacement can be split into two components for assessment: the proportion of the population that are displaced from the development and the magnitude of the demographic consequences on colony SPAs that arises from displacement and barrier effects.
Estimates of the former have been obtained primarily from at-sea surveys. Studies have shown marked variation in barrier effects and displacement among species. However, they have also shown substantial variation within species among studies, suggesting that effects are highly context dependent. One potential cause of this variation is intrinsic differences among individuals in different populations studied, for example the extent to which they are central place foraging or operating as independent individuals. However, another potential cause is the challenge in obtaining robust quantification of displacement and barrier effects. In particular, these quantifications rely on key assumptions, arguably the most important of which is that the relative differences in density of birds inside and outside the wind farm are due to displacement or barrier effects, when alternative explanations such as the relative distribution of prey are equally plausible.
Such studies based on monitoring surveys are also not structured to address the second component outlined above - the magnitude of demographic consequences. The absence of empirical data has necessitated the use of a precautionary approach to assessments. When based on well-grounded assumptions and reliable parameter estimates, individual-based simulation models can provide a valuable framework for estimating the demographic consequences of a variety of environmental perturbations. As such, this approach can be used to estimate demographic effects for seabirds of offshore renewable developments (ORD) mediated via the costs of barrier effects and displacement, whilst incorporating the uncertainty surrounding these estimates. This project sought to develop an analytical tool that uses this approach to quantify the demographic consequences of displacement and barrier effects, thereby improving the precision of assessment of ORD impact on seabirds so that regulatory bodies and their statutory advisors can reach informed, evidencebased decisions on the potential impacts of renewable developments whilst also encouraging sustainable use of the sea, consistent with the Scottish Government's twin goals of meeting its obligations with respect to climate change mitigation and safeguarding the marine environment.