Birds in southern Öresund in relation to the wind farm at ... - Vattenfall

Fig. 24. Summary distribution maps for the Eider Somateria mollissima from boat surveys
pre- (left) and post- (right) construction of the wind farm. For annual maps see appendix.
Sammanfattande utbredningskartor för ejder Somateria mollissima från båtinventeringar före
(vänster) och efter (höger) uppförandet av vindkraftparken. För årsvisa kartor se appendix.
Overall Jacob’s indices for the wind farm area and the 2 km buffer zone show somewhat
different results compared to the density analysis above (Table 3). The aerial survey data
show more or less unchanged D-values from the pre- and post construction period in total
(0.06 and 0.08 for the wind farm area, 0.79 and 0.69 for the buffer zone respectively)
indicating that irrespective of the presence of the wind farm, the Eiders used the wind farm
area as expected and preferred the buffer zone. The boat survey data however indicated a
similar pattern as the density analysis with preference for the wind farm area during the preconstruction
period changing to expected use with the wind farm in operation (D = 0.80 pre,
-0.09 post). The overall change was in the same direction for the buffer zone where preference
changes to more or less expected use (D = 0.68 pre, 0.11 post).
Explanations for these unclear, and in relation to the density analysis above conflicting,
results can be found in a more detailed look at Jacob’s indices from the different years
separately (Fig. 26). Apparently there was a clear avoidance of the wind farm area during the
first years with the wind farm in operation (low indices 2007-2009) while the area was
preferred (aerial survey data) or used as expected (boat survey data) in 2011. This could be a
sign of habituation to the presence of the wind farm although others factors, such as changes
in food availability, can be involved as well.
Further indications of habituation of Eiders to the wind farm was that during the spring aerial
survey in 2011 flocks of a few hundred Eiders were found in the wind farm but outside the
survey belt and hence not included in any of the figures above. This was the first observation
of larger flocks inside the wind farm during operation.
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