VULNERABILITY OF SCOTTISH SEABIRDS TO OFFSHORE WIND

3. VULNERABILITY FACTORS FOR OFFSHORE WIND FARMS

Garthe and H◘ppop (2004) assigned scores for the various component factors on a scale of 1 to 5 where 5 is a strong anticipated negative impact. It is assumed that these individual factor scores can then be summed to give a total for each species that ranks species according to their vulnerability with regard to offshore wind farm developments. Six factors were scored by Garthe and H◘ppop (2004), representing potential negative effects of offshore wind farms on seabirds or sensitivities of the ecology of seabird species. We have used the same six factors, but have arranged these differently to take account of a concensus view that some of the factors used by Garthe and H◘ppop (2004) were of uncertain and possibly low relevance, while one (flight height) is of very high importance. These factors relate primarily to collision risks and habitat loss through avoidance. However, there are other possible impacts that are not necessarily covered by this set of factors. For example, Perrow et al. (2011) presented evidence suggesting that little tern breeding success in a colony in Norfolk may have been reduced by a shortage of young herring around Scroby Sands offshore wind farm caused by monopile installation affecting fish reproduction locally. To an extent, the high sensitivity of little tern would be indicated by our six factors because they are seabirds with a very short foraging range that utilize a very particular and restricted foraging habitat, so score as sensitive on the habitat flexibility factor, but complex and indirect ecosystem effects such as alteration of fish abundance by wind farms is something that is extremely difficult to predict. There may also be predictions that, once operational, such offshore wind farms may enhance food supplies for seabirds by acting as marine protected areas (e.g. closed to trawl fishing). Such indirect and uncertain effects are beyond the scope of this review, but should not be assumed to be negligible. The six factors included are listed in turn in the following sections (following the same sequence as originally presented in Garthe and H◘ppop, 2004).