VULNERABILITY OF SCOTTISH SEABIRDS TO OFFSHORE WIND

3.1 Flight manoeuvrability (Factor 1)

This factor takes into account the aerial agility of species and hence their potential to avoid collision with wind turbines at sea, although other factors such as their visual perception may also play a role in this (Martin and Shaw 2010, Martin 2011). The perception of risk, which seems to vary among species, and may possibly be as important a factor as anatomical constraints may also be relevant, but cannot readily be scored on a scale. Scores were taken from Garthe and H◘ppop (2004) for those species listed in that paper, but adjusted where more recent data suggest appropriate. For additional species, scores were based on a review of the literature and on subjective judgement moderated by expert opinion. Species were classified from 'very high flight manoeuvrability' (score 1) to 'very low manoeuvrability' (score 5) ( Table 5). Much of the variation in this factor among species is due simply to their anatomy (Pennycuick 1987). A large tail allows better manoeuvrability. A low wing loading allows slow flight and greater acceleration. A fast-flying species with high wing loading (heavy body mass, small wing area and short tail) is unable to manoeuvre rapidly (for example, common guillemot, great northern diver) whereas a slow flying species with a large tail area is able to be highly agile (for example Arctic tern, kittiwake). So, for example, little auk and puffin score marginally lower than razorbill and guillemot because their wing loadings are significantly lower so should make them slightly better at avoiding objects in flight. Following Garthe and H◘ppop (2004), we assume that, other factors being equal, birds with low flight manoeuvrability are more likely to collide with wind turbines at offshore wind farms than are birds with high flight manoeuvrability. Nevertheless, collisions are apparently extremely rare. Petterson (2005) reported one death by collision of an eider duck out of some 2 million sea ducks that flew past an offshore wind farm in southern Kalmar Sound, Sweden. There is also a view that flight manoeuvrability may be less important in determining collision risk than had been thought, and that other aspects of avian perception may be more important. For this reason, this factor was given a lower weighting than had been the case in Garthe and H◘ppop (2004), as discussed in section 3.7.

Table 5. Flight manoeuvrability scores