Supporting a Strategic Environmental Assessment
Despite the imperative presented to national governments to attain their Kyoto targets, development of offshore energy resources requires an international, national and regional SEA of the most suitable areas for such exploitation. Ideally, the first strategic level approach should determine the relative avian nature conservation interest of European marine waters, to establish a core overview of differential importance and therefore sensitivity. After this, the economic constraints on the suitability of different potential OWF sites to deliver power into the national grid can be considered in order to provide a ‘wish list’ of potential development sites, to compare against known avian distributions and assess the likely impacts on birds. From the industry side, this wish list would be compiled based upon the available wind resources in relation to the costs of offshore developments in the best areas. Constraints upon this would include, for example: water depth; substrate type; distance to shore; suitability of grid connections; and costs of transmission to distant centres of population etc. Such a ranking of feasible and cost-effective sites for development would then offer up a first level list of proposed sites for the consideration and assessment of potential consequences for, and interactions with, a range of other stakeholders and user-groups. Some of the issues necessitating wide consultation with appropriate stakeholders and statutory bodies (which lie outside the scope of this review) would include: conflicts with shipping lanes, military, fisheries, oil and gas industry, telecom linkages and many others. However, the first level of screening and consultation would include an assessment of the nature conservation values of the site, with regards to the statutory obligations directed by domestic and European legislation. From the avian conservation viewpoint, it is essential that the bird interest of a particular proposed wind farm site can be assessed in the international, national and regional context. This necessitates at least some idea of the distribution of resting and feeding birds in all sea areas during critical periods of the annual cycle (taken here to be wintering areas, spring staging areas, nesting and breeding feeding areas, moulting areas and autumn staging areas).
In Denmark, extensive data on the relative distribution of birds at sea were available from aerial census data supplemented with boat-based surveys available since the 1970s (e.g. Joensen 1973, 1974, Durinck et al. 1994, Laursen et al. 1997). These data formed the basis upon which to make a preliminary assessment of the favoured sites for development of wind energy in the sea. Such extensive knowledge enabled a first level assessment of the relative suitability of the five proposed wind farm sites in Denmark.
In most European states, such extensive knowledge of resting and feeding bird distributions at sea are generally lacking. Notable exceptions include those areas covered by the European Seabirds at Sea (ESAS) database (and associated analyses, e.g. Blake et al. 1984, Tasker et al. 1987, Carter et al. 1993, Mitchell et al. 2004) and/or subject to special monitoring (e.g. designated Special Protection Areas notified under the EU Birds Directive). However, ESAS coverage can be patchy, especially in shallower waters inshore. It is then neccessary for some phase 1 level survey of extensive areas of marine waters in order to make proper assessments of the relative importance of proposed sites. The ideal objectives of such a survey would be: to cover as large an area as possible in the time available; to sample as simultaneously as possible; use the greatest level of spatial precision possible; and to use observation platforms that create the least disturbance to abundance and distribution patterns. Suitable methods for achieving this, using transect grid coverage by aerial surveys, have been described by Camphuysen et al. (2004). Transect sampling of bird abundance based on counts from moving platforms, corrected for detectability using distance sampling approaches (Buckland et al. 2004) offers a very powerful tool for generating bird density surfaces. This is especially so when using spatial modelling techniques (such as generalized additive and mixed modelling) to incorporate environmental parameters as covariates to explain bird distributions and abundance (e.g. Hedley et al. 1999, Clarke et al. 2003). Such approaches offer the possibility to sample bird distributions using sparse transect coverage to interpolate modelled densities with confidence as a phase 1 survey (Camphuysen et al. 2004). These methods offer the opportunity for an objective ranking of ‘hot spots’ of high bird concentrations at particular times during the annual cycle or at least identify areas in need of more intensive survey.
Whilst such survey is ideal for defining the distribution of birds exploiting the sea for feeding or resting, instantaneous sampling is poor at defining avian migration intensity over large areas of open sea. Flight movements of birds between areas (especially during long distance migration and foraging flights between breeding sites, feeding areas and roosting sites) are by definition intense and of very short duration at various different altitudes, heavily dependent on season and weather. However, assessments of bird movements at local, small spatial scales (but set in a national or regional context) are required for the effective assessment of, for example, collision risk probabilities. Where terrestrial birds, as well as waterbirds, can be shown to migrate in very low densities, the local collision risk can be considered very much lower than in cases where large densities of birds migrate at turbine height through a proposed site. It is well known, for example, that migrants collect at the tips of peninsulas throughout the world prior to crossing the sea (e.g. Foy 1976, Alerstam 1990). Waterbirds are also concentrated by topography (e.g. Common Eiders Somateria mollissima at Nysted, Kahlert et al. 2004) or gather at sea prior to crossing the land (Bergmann & Donner 1964, Bergmann 1974). Hence, it is likely that topography shapes migration routes out at sea, at least in near shore areas. Similarly, it is known that migrating birds crossing the sea may lose or gain height upon approaching land (e.g. Richardson 1978, Alerstam 1990). Any knowledge of the migration corridors and patterns of flight in three dimensions across the open sea (especially in near shore areas where wind farm development is most likely) is highly desirable to support effective siting of wind farms to avoid high collision risk areas.
Unfortunately, such data are not extensively or readily available in Europe. Only military, air traffic control or meteorological radars can currently provide sufficient coverage of mass migrations of birds over time at large spatial scales (i.e. 1–200 km), over a range of altitudes (Gauthreaux 1970, Desholm et al. 2005). Some species specific radar studies have been undertaken in Europe (e.g. Alerstam et al. 1974) using weather radar (e.g. in Finland & Koistinen 2000) or military radar (e.g. in Sweden, L. Nilsson pers. comm., and Germany, O. Hüppop pers. comm.). However, the results have not been fully published and because the quality of data on bird migration altitude is variable, are generally not in a form suitable to support SEAs. There are a number of problems associated with using such radars, not least the conflict of interest, given that meteorological, air traffic control and military radars frequently filter out the signals reflected by birds. The operational lack of capability to distinguish bird migration at low (i.e. turbine sweep) altitudes is frequently another disadvantage of using such technology (Desholm et al. 2005). Nevertheless, the use of these existing sources of data and the development of specific bird radar equipment has the potential to deliver vital information in the future. Both could potentially be used to support the identification of migration corridors (e.g. those associated with promontories and peninsulas where birds tend to arrive and depart from) and the flight behaviour of birds (especially flight altitude) in the vicinity of proposed wind farm sites. This information is needed both to inform the SEA process and influence the local siting of turbines as pre-construction mitigation during the EIA process.
At present, there have been very few attempts in Europe to undertake a SEA associated with OWF development, despite the fact that the legislative framework requires this to be undertaken. Many of the specific environmental issues associated with a development will be addressed at site level by a project-specific EIA. A strategic assessment of where best to locate OWFs in national waters, to avoid specific conflict with resting and feeding waterbirds has only been undertaken in Denmark, Germany (the MINOS project, ‘Marine warm-blooded animals in the North and Baltic Seas: foundation for assessment of offshore wind farms’) and regionally in the UK. To the best of our knowledge no strategic national assessment of avian migration routes has been undertaken in this connection, with the exception of current studies in Germany (see Exo et al. 2003).