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

Long-tailed Duck Clangula hyemalis
.
The Long-tailed Duck was regularly seen during the surveys in the study area but the numbers
counted were generally relatively low (Fig. 14 & 15). The majority of the Long-tailed Ducks
were counted in the reference area south of Falsterbo, whereas only smaller numbers occurred
in Öresund. In the southern area more than 1000 individuals were sometimes counted in the
survey belt, whereas maximum counts from the northern parts were around 100, up to 200
and a little more being maximum counts from the boat surveys.
Long-tailed Ducks were regularly seen at Lillgrund before the construction of the wind farm,
larger numbers being seen at the boat counts than during aerial surveys (Fig. 16 & 17). In the
post-construction years only few Long-tailed Ducks were counted in the wind farm area and
the density was much lower in both the wind farm area and in the 2 km buffer zone (Fig. 18).
Numbers counted in the different zones (used for the density calculations) was generally low.
In the windfarm area a mean count of two individuals was obtained for the three surveys in
2006, whereas only one Long-tailed Duck was seen during nine censuses post-construction.
Total number of Long-tailed Ducks counted within the buffer zone varied between four and
seven, whereas between 32 and 77 were counted at aerial surveys in the outer area. For further
details see Table A10 in the appendix. Spring numbers were too low to calculated densities
for this species.
The same pattern emerges when we look at the Jacob’s indices in Table 4. During the boat
surveys a certain amount of preference was recorded for the wind farm area during the preconstruction
period (D = 0.48), which changed to a weak avoidance for the post-construction
years (D = -0.14). The direction of the change was similar based on data from the aerial
surveys although Jacob’s index indicated a weak avoidance already before the construction of
the wind farm (D = -0.23). Post construction a much stronger avoidance was indicated (D =
-0.85). Based on data from the buffer zone, up to 2 km from the wind farm, the two survey
methods yielded different overall results. While the boat surveys showed preference for these
parts both before after construction of the wind farm (D = 0.78 and 0.77 respectively), the
aerial surveys showed that the buffer zone was used as expected during the pre-construction
period but less than expected (avoided) with the wind farm in operation (D = 0.06 and -0.41
respectively).
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