- Migratory birds move across seas in large numbers but over a short time period, often at night and sometimes in bad weather, so are not adequately recorded in bird surveys undertaken as part of Environmental Impact Assessments (EIAs) for proposed offshore wind farms. As such, the possible effects of these developments on migratory birds are not well understood.
- A comprehensive review of the literature on bird migration (particularly around the UK) was undertaken in an attempt to identify gaps in our knowledge and make recommendations for future research. The review focussed on species that are designated features of UK Special Protection Areas (SPAs), and other regularly occurring species listed on Annex 1 of the Birds Directive, as agreed with the SOSS steering group. This does not mean that other migratory bird species should not be considered in impact assessments, but they are not included in the scope of this report.
- Information was sought on migratory routes and population sizes, along with details of flight altitudes and the frequency of fall events, which were thought likely to influence a species’ vulnerability to collision with wind turbines.
- The review showed that although a large number of species migrate across UK waters, for the majority of them our knowledge of migratory behaviour is limited and does not allow estimation of the proportion of birds migrating at heights where they may encounter wind turbines.
- Although the migratory destinations on land are quite well understood for many species, details of the routes that they follow when flying over the sea around the UK are rarely known. This means it is difficult to estimate the numbers of birds likely to fly over proposed offshore wind farm sites, particularly for species that use more than one migratory pathway across UK waters.
- We have provided guidance on methods to assess the potential risk to migratory birds that are features of SPAs from proposed offshore wind farm developments. Whilst this guidance is currently limited to migratory SPA species, this does not preclude the future need for assessment of other species.
- We have made recommendations for future work to address some of the current gaps in knowledge that pose a potential risk to consenting for offshore wind farm developments. We suggest that future work should initially concentrate on those species that are features of SPAs, and whose entire biogeographic population migrates across UK waters, in particular if initial assessment using the guidance in this report suggests that there is a potential risk to the species in question. The importance of work on other species should also be considered in these terms, such that studies of species for which negligible risk is identified using the methods suggested in this report, and of non-SPA species and/or those species for which only a small proportion of the population is found in UK waters are not prioritised.
- Where suitable technology exists, studies combining the use of tags with radar could be particularly valuable in informing our understanding of a species’ migratory behaviour. Studies combining weather data with radar observation of migrating birds would also be very valuable.